Crocodylus niloticus Laurenti 1768

Crocodylus niloticus

Crocodylus niloticus

Die Nylkrokodil (Crocodylus niloticus) is die grootste van die vier krokodilspesies wat in Afrika voorkom. Die krokodille het lang sterte en kragtige kake. Hulle agterpote is geweb om hulle te help swem. Hulle word tot 6 meter lank en kan tot 1000 kg weeg.^[1] Die mannetjies is gewoonlik groter as die wyfies.

Nylkrokodille kom wydverspreid oor Afrika suid van die Sahara en in Madagaskar voor. Hulle het vantevore selfs in die Middellandse See, Israel en Jordanië voorgekom. Hierdie krokodille leef in verskillende habitats, insluitend mere, riviere en riviermondings.

Onvolwasse nylkrokodille vreet insekte en klein vissies. Die volwasse nylkrokodille vang groter diere om te vreet, soos sebras, wildsbokke, wildebeeste en buffels,^[1] en vreet ook mense.

Dié krokodille paar in die water, waarna die wyfie 'n gat in die grond grawe waarin sy haar eiers lê. Hulle kan tot 60 eiers lê wat ongeveer 90 dae neem om uit te broei.^[1] Die wyfie pas die nes gedurende hierdie tyd op. Jong krokodille kan vanaf 12-jarige ouderdom voortplant.^[1]

Verwysings

Hierdie artikel is ’n saadjie. Voel vry om Wikipedia te help deur dit uit te brei.

Krokodil an Nil (Crocodylus niloticus) a zo ur stlejvil hag a vev el lodenn vrasañ eus Afrika issahara hag en Egipt.

Tento článek není dostatečně ozdrojován a může tedy obsahovat informace, které je třeba ověřit.
Jste-li s popisovaným předmětem seznámeni, pomozte doložit uvedená tvrzení doplněním referencí na věrohodné zdroje.

Krokodýl nilský (Crocodylus niloticus) je nejhojnější a nejznámější druh krokodýla, patří rovněž k druhům, dorůstajícím největší velikosti. Vyskytuje se na většině území Afriky a v Izraeli. Navzdory lovu i úbytku stanovišť zatím nepatří mezi ohrožené druhy. Pro svou kůži i maso se chová na krokodýlích farmách po celém světě.

Pojmenování

Vědecký název Crocodylus niloticus dal zvířeti roku 1768 rakouský přírodovědec Josph Nicolaus Laurenti, toto pojmenování však má antické kořeny. Slovo krokodýl pochází z řečtiny a poprvé je doloženo v díle Hérodota. Doslova znamená "dlážděný červ", což má odkazovat na tvrdé hřbetní destičky. Už starověcí autoři jako Diodóros Sicilský používali označení crocodylus niloticus, tedy doslova nilský dlážděný červ. Podle pozdně antických Etymologií Isidora ze Sevilly je slovo crocodylus odvozeno od květiny krokusu, protože krokodýli mají stejně žluté břicho jako šafrán, získávaný z krokusu. Tento výklad však není obecně přijímán.

Afričtí domorodci nazývají krokodýla nilského mnoha názvy. V Súdánu je krokodýl znám pod arabským názvem timsah, v západní Africe ho Hausové nazývají kada a Jorubové öni, ve východní Africe je znám pod svahilským názvem mamba, v Burundi je nazýván ingona, v Kongu ho mluvčí jazyka lingala nazývají nkóli, v jižní Africe ho Zuluové, Khosové, Tswanové či Vendové nazývají ngwena či kwena a Malgaši na Madagaskaru mu dali jméno voay.

Popis

Krokodýl nilský patří mezi největší druhy krokodýlů. Za vhodných podmínek může dorůst délky až okolo 6,5 m a hmotnosti 1100 kg, ale jedinci delší než cca 5 m jsou extrémně vzácní. Největší žijící krokodýl nilský se jmenuje Gustav a žije ve volné přírodě na řece Ruzizi v Burundi, při posledním pozorování roku 2008 měřil více než 610 cm a vážil asi 1000 kg.^[zdroj?] Pohlavní dimorfismus je spíše nevýrazný, spočívá především ve velikosti; samci zpravidla dorůstají větších rozměrů než samice. Samci měří v průměru okolo 4 metrů, samice mírně přes 3 metry.

Jako všechny druhy krokodýlů má krokodýl nilský kůži pokrytou hranatými šupinami, které se vzájemně nepřekrývají. Ty jsou na hřbetě a ocase podloženy kostními štítky (osteodermy), zatímco na hlavě je kůže pevně přirostlá k lebce. V zadní části hřbetu a na ocase tvoří šupiny dvojitý hřeben, který asi ve dvou třetinách délky ocasu splývá do jediného, vyššího hřebenu. Vzhledem k tomu, že pod kůží na břiše nemá vyvinuty osteodermy (tvrdé kostěné štíty), jeho kůže se hodí pro komerční využití. Z toho důvodu je hojně loven a rovněž chován na farmách.

Zbarvení je olivově zelené, šedé až modrozelené, často s tmavými skvrnami a proužky, především na bocích. Břicho je žlutavé, světle zelené nebo špinavě bílé. Končetiny jsou silné, přední mají pět prstů, zadní mají prsty jen čtyři, spojené malou plovací blánou. Hlava krokodýla nilského je dlouhá a poměrně široká, na konci poněkud zúžená. Počet zubů je 64 až 68, čtvrtý spodní zub vyčnívá, jako u všech krokodýlovitých, ze zavřené tlamy. Zuby jsou kuželovité a neumožňují žvýkání. Zuby jsou zasazeny do jamek v čelistech (thekodontní typ chrupu) a během života se poměrně často vyměňují. Velcí, staří krokodýlové během života prodělali výměnu zubů nejméně čtyřicetkrát.

Způsob života

Krokodýl nilský žije obvykle samotářsky, i když na vhodných stanovištích dosahuje jeho populace značné hustoty. Samci jsou teritoriální a zejména v období páření neváhají napadat jiné krokodýly. Přes den se krokodýli nejčastěji sluní na břehu, odkud při vyrušení prchají do vody. Nejaktivnější jsou za soumraku, kdy také zpravidla loví. Přestože krokodýl na souši působí neohrabaně, při útěku nebo útoku na kořist dokáže vyvinout značnou rychlost. Ve vodě krokodýl nilský plave horizontálním vlněním dlouhého ocasu. Při útoku na kořist se krokodýl dokáže prudce vymrštit z vody do výšky 1-2 m. K odpočinku si krokodýli nilští vyhrabávají pod břehem prostorné nory, které mohou měřit až 10 m. Zde přečkávají i dlouhotrvající sucha nebo období nedostatku potravy, často i více zvířat pohromadě.

Ke v vzájemné komunikaci využívají krokodýlové širokou škálu optických, akustických a pachových signálů. Podčelistní pachové žlázy se uplatňují zejména v době páření. Na rozdíl od většiny plazů mají krokodýlové nilští poměrně široký hlasový repertoár. Samci v období páření hlasitě řvou, mláďata při líhnutí komunikují s rodiči zvláštním kvákáním, které se podobá kvákání kachny. Při ohrožení mláďata přivolávají matku kvákáním a pištěním.

Mezi krokodýlem nilským a některými ptáky, zejména kulíkem nilským (Pluvianus aegyptius) a čejkou ostruhatou (Vanellus spinosus) existují komenzální vztahy, podobně jako mezi velkými africkými savců a klubáky či volavkou rusohlavou. Ptáci se pohybují mezi krokodýly, slunícími se na břehu, odstraňují jim parazity i zbytky potravy, uvázlé mezi zuby. Mohou krokodýly rovněž varovat před nebezpečím.

Rozšíření

Krokodýl nilský se ve starověku vyskytoval v celé Africe, na Madagaskaru a na Blízkém východě, např. v řece Jordán. V Egyptě a v asijské části svého areálu však byl v průběhu 19. století vyhuben. V současné době se vyskytuje v Africe jižně od Sahary, od Mali, Senegalu a Súdánu až po Kapsko. Na Madagaskaru je poměrně vzácný, v Izraeli byl reintrodukován koncem 20. století. Je vázán na vodní plochy, především řeky a jezera, k životu mu ale stačí i rozsáhlejší bažina. Izolovaná populace žije dokonce i saharských oázách pohoří Tassíli. Zdejší krokodýli dosahují délky jen do 2 m a jejich populace je ohrožena vyhubením. Na Madagaskaru žije i jeskynních řekách (např. rezervace Ankarana) a nevyhýbá se ani brakické vodě.

Potrava

Krokodýl nilský je výlučně masožravý. Skladba potravy se mění v závislosti na věku a velikosti krokodýla. Mláďata do délky 1 m se zdržují při břehu, kde loví především hmyz (přes 60% potravy), dále žáby, korýše, pavouky či malé rybky. Starší zvířata v délce 1-3 m se živí téměř výhradně rybami, jen malá část potravy připadá na korýše, měkkýše, žáby, vodní hmyz a drobné savce či plazy. Dospělá zvířata dorůstající 4-6 m loví velké ryby (zvláště sumce, okouna nilského, bahníky), želvy a jiné plazy, vodní ptáky, ale také savce, až do velikosti žirafy, buvola, mladého hrocha či slůněte. Častější kořistí jsou však pakoně, prasata bradavičnatá, vodušky, sitatungy či jiné antilopy.

Menší kořist krokodýl usmrtí stiskem čelistí, větší savce obvykle uchopí za přední končetinu nebo za čenich, stáhne pod hladinu a utopí. Protože krokodýli nemohou žvýkat, trhají kořist nejčastěji tak, že se pevně zakousnou a pak otáčením kolem své osy vytrhnou kus masa. Větší úlovek často ukládají v norách pod podemletým břehem , kde ho konzumují několik dní. Konzumují také mršiny, naproti tomu kanibalismus je pouze výjimečný. Krokodýl má v čelistech mimořádný stisk, dosahující síly až 13 kN.

Rozmnožování

V období páření krokodýli vydávají bučivé zvuky, zesiluje také jejich pach. v obou případech se jedná o prostředky komunikace mezi pohlavími. Po páření, které probíhá ve vodě, si samice na břehu vyhrabe jámu, hlubokou asi 50-80 cm. Do ní naklade 20 až 80 vajec, která zahrabe. Počet vajec závisí na velikosti a kondici samice. Vejce mají ovální tvar a měří asi 8 x 6 cm. Po nakladení jámu s vejci samice zahrabává. Pohlaví mláďat není dáno geneticky, ale závisí na teplotě, při níž se vejce inkubují (podobně jako u mnoha druhů želv a některých ještěrů). Při teplotách nižších než 29 stupňů Celsia se líhnou samičky, při teplotě kolem 30 stupňů je poměr pohlaví vyrovnaný, při vyšších teplotách převažují samci. Inkubace zpravidla trvá 85-95 dnů. Po celou dobu inkubace samice snůšku obvykle hlídá před predátory, přesto mnoho vajec padne za oběť dravým ptákům, čápům marabu, varanům nilským, hyenám, promykám či paviánům. Po vylíhnutí mláďata přivolávají matku kvákavými zvuky. Samice mláďatům pomáhá vyhrabat se z jámy a často je v tlamě odnáší do vody, kde je nějakou dobu (1-5 měsíců) hlídá. U příbuzných druhů bylo pozorováno, jak v období sucha samice převádí mláďata z vysychajícího jezírka do řeky.

Krokodýli a člověk

Staří Egypťané uctívali boha řeky Nilu jménem Sobek, jenž byl zobrazován s hlavou krokodýla. V jeho chrámech byli chováni krokodýli, které věřící krmili. Uhynulé krokodýly Egypťané také balzamovali. Krokodýlí kult ale nebyl rozšířen v celém Egyptě a místy, zvláště v Horním Egyptě, byli krokodýli naopak loveni a pojídání. V římské době byl krokodýl symbolem Egypta a jeho obraz se objevoval i na mincích. Římané krokodýly zneužívali při hrách v cirku. Zde byli krokodýli zabíjeni, štváni proti jiným zvířatům nebo jim byli předhazováni odsouzenci.

Ve středověkých bestiářích či Mandevillově cestopise se tradovalo mnoho představ o krokodýlech, kteří zabíjejí lidi a před jejich pozřením roní pokrytecké slzy, podle jiných legend žere krokodýl pouze muslimy a pohany, zatímco křesťanů si nevšímá.

V Africe a na Madagaskaru mnohé kmeny pokládají krokodýly za své předky, nebo věří, že se zemřelí lidé proměňují v krokodýly. Krokodýlí kult je dosud rozšířen např. mezi Šilúky v Jižním Súdánu, u etnika Dan v Pobřeží slonoviny nebo u Mossiú v Burkině Faso. Někde, zvláště na Madagaskaru nebo v oblasti Velkých jezer (království Buganda a Buňoro) byli krokodýlové používáni k ordálům, při nichž měl obviněný proplavat mezi krokodýly. Po celé Africe jsou rozšířeny představy o čarodějích, kteří se mohou teriantropicky proměňovat v krokodýly nebo je alespoň ovládat. V oblasti Pobřeží slonoviny, Libérie a delty Nigeru existovaly tajné společnosti krokodýlích lidí, kteří nosili krokodýlí masky a provozovali obřady, včetně rituálních vražd a kanibalismu (obdoba známějších společností Levhartích lidí).

K lovu krokodýlů slouží v Africe především udice s velkým dvojhákem, případně harpuna, loví se rovněž odstřelem, především v noci, za pomoci reflektoru, kterým lovci krokodýly oslní. Dost rozšířené jsou i krokodýlí farmy, které se objevují v poslední době i v Evropě. V České republice jsou zastoupeny kontroverzním podnikem ve Velkém Karlově na Znojemsku. Využívá se kůže, především z břišních partií a také maso. Afričtí domorodci využívají pachové žlázy, tuk i orgány krokodýlů k magickým, medicínským nebo kosmetickým účelům. Vzhledem k velkým rozměrům a relativně rychlému růstu se krokodýl nilský nehodí pro chov v bytových podmínkách. Rovněž v ZOO se s ním setkáváme poměrně zřídka, v České republice je chová jen krokodýlí ZOO Protivín.

Reference

1. ↑ Červený seznam IUCN 2018.1. 5. července 2018. Dostupné online. [cit. 2018-08-10]

Literatura

• Moravec, Jiří: Svět zvířat VII. - Obojživelníci, Plazi. Praha: Albatros, 1999.
• Vágner, Josef: Afrika, ráj a peklo zvířat, Praha, 1990.

Externí odkazy

• Obrázky, zvuky či videa k tématu krokodýl nilský ve Wikimedia Commons

Crocodylus niloticus

Crocodylus niloticus

Nilkrokodille (Crocodylus niloticus) er en af 4 arter krokodiller i Afrika, og den næststørste af arterne. Nilkrokodillen findes i det meste af Afrika syd for Sahara, og på øen Madagaskar. Nilkrokodillen kan blive op til 6.50 m lang og veje 1100 kg, De største eksemplarer er blevet målt i Tanzania og var 6,45 m lange og vejede 1090 kg.^[2]

Nilkrokodillen er et af de dyr på jorden med den kraftigste bidestyrke. Den bider med 3500 kg/cm².^[3] Til sammenligning er menneskets bidestyrke på 105 kg/cm².

Kilder og eksterne henvisninger

• Wikimedia Commons har flere filer relateret til Nilkrokodille

Crocodylus niloticus

Das Nilkrokodil (Crocodylus niloticus) ist eine Art der Krokodile (Crocodylia) aus der Familie der Echten Krokodile (Crocodylidae). Die normalerweise 3–4 m lang werdende Art bewohnt Gewässer in ganz Afrika und ernährt sich größtenteils von Fischen. Gelegentlich können Nilkrokodile jedoch auch große Säugetiere (z. B. Zebras) unter Wasser zerren und ertränken. Das Nilkrokodil betreibt intensive Brutpflege, die Mutter bewacht ihr Nest und beschützt die Jungtiere in den ersten Lebensmonaten. Die Art nahm eine wichtige Rolle in der ägyptischen Mythologie ein und war einst wegen starker Bejagung gefährdet. Nachdem die Jagd in den 1980ern verboten wurde, haben sich die Bestände weitgehend erholt.

Merkmale

Das Nilkrokodil ist das größte Krokodil Afrikas und erreicht normalerweise Längen von 3 bis 4 m.^[1] Große Weibchen werden über 2,8 m lang, während große Männchen über 3,2 m lang werden können.^[2] Sehr selten werden über 6 m Länge erreicht, als Maximum gelten 6,5 m. Die Schnauze ist 2-mal so lang wie an der Basis breit. Der Ruderschwanz ist kräftig und seitlich abgeflacht. Erwachsene Nilkrokodile sind oberseits dunkel-olivfarben, der Bauch ist einheitlich porzellanfarben. Die Jungtiere sind hell olivfarben und dunkel gefleckt und gebändert. Die Färbung der Krokodile wird stark von den im Wasser gelösten Stoffen beeinflusst.

Verbreitung, Lebensraum und Unterarten

Verbreitung des Nilkrokodils

Das Nilkrokodil bewohnt nahezu ganz Afrika inklusive Madagaskar, fehlt aber im äußersten Südwesten Afrikas, in der Sahara (bis auf ein isoliertes Vorkommen im Guelta d’Archei) und im Osten Madagaskars. Früher bewohnte es auch den Nil auf der gesamten Länge, findet sich heute aber nur noch im Oberlauf bis Assuan. Die Art bewohnt zahlreiche Lebensräume, so etwa Flüsse, Teiche, Seen, Sümpfe und Mangroven.

Es werden aktuell sieben geographische Unterarten unterschieden. Genetische Untersuchungen führen zu Spekulationen, dass möglicherweise einige davon auch als eigene Arten anzusehen sind:^[3]

• Crocodylus niloticus africanus: Südliches Tansania, Sambia, Malawi, Mosambik, östliches Namibia.
• C. n. chamses: Äquatorialguinea, Gabun, Republik Kongo, Zaire, südlicher Sudan, Uganda, Ruanda, westliches Tansania, nördliches Sambia, Angola, nördliches Namibia.
• C. n. cowiei: Simbabwe, Botswana, Südafrika.
• C. n. madagascariensis: Madagaskar.
• C. n. niloticus: Südliches Ägypten, Sudan, westliches Äthiopien.
• C. n. pauciscutatus: Östliches bis südliches Äthiopien, Somalia, Kenia.
• C. n. suchus: Südliches Mauretanien, Senegal, Gambia, Guinea, Ghana, Togo, Benin, Nigeria, Kamerun, Burkina Faso, Mali, Niger, Tschad, Zentralafrikanische Republik. (Wird inzwischen als eigenständige Art angesehen, siehe: Westafrikanisches Krokodil (Crocodylus suchus)^[4])

Die Unterarten werden anhand ihrer Pholidose unterschieden.

Nilkrokodile wurden in den letzten Jahren auch vereinzelt in den Everglades in Florida gesichtet. Man vermutet, dass diese durch den Menschen illegal eingeschleppt worden sind und sich dort als Neozoon vermehrt haben.^[5]

In historischer Zeit kam das Nilkrokodil auch in Algerien, Israel und den Komoren vor.^[6]

Lebensweise

Aktivität

Nilkrokodil

Tagsüber sonnen sich Nilkrokodile meist am Ufer, nachts gehen die Krokodile ins Wasser. An den großen afrikanischen Flüssen, die nicht saisonal austrocknen, sind Nilkrokodile das ganze Jahr über aktiv. In saisonal austrocknenden, kleineren Gewässern lebende Krokodile bleiben wesentlich kleiner (2,4–2,7 m) als Krokodile in permanenten Gewässern. Sie verbringen die Trockenzeit in 9–12 m langen Erdhöhlen, die in einer Kammer mit einigen Luftlöchern enden. In einer solchen Kammer überdauern bis zu 15 Krokodile die Trockenheit.

Ernährung

Nilkrokodile gehen nachts ins Wasser um zu jagen – sie sind generalistische Fleischfresser. Der Hauptbestandteil der Nahrung adulter Nilkrokodile ist Fisch; im Rudolfsee im Norden Kenias machen Fische 90 %,^[3] im Okavango-Delta von Botswana bei subadulten Exemplaren 68 % der Nahrung aus.^[7] Weitere Beutetiere sind Vögel, Schildkröten und kleine Säuger.^[1] Große Nilkrokodile können auch Großsäuger erjagen. Sie lauern der Beute meist unter den Oberflächen von Flüssen oder Wasserstellen auf, an denen die Tiere zum Trinken eintreffen, und bleiben durch das flache Profil des Kopfes und die nahezu geräuschlose Fortbewegung unbemerkt. Das Opfer wird dann angesprungen, im Sprung gepackt, ins Wasser gezerrt und ertränkt. Unter anderem wurde von Zebras, Antilopen, Stachelschweinen, jungen Flusspferden und auch Raubtieren wie Hyänen oder Löwen berichtet, die von Nilkrokodilen erbeutet worden waren.^[1] Aas gehört ebenfalls zur Nahrung des Nilkrokodils.

Junge Nilkrokodile ernähren sich von deutlich kleineren Beutetieren. Einjährige Nilkrokodile im Okavango-Delta ernähren sich zu 45,6 % von Insekten und Spinnen, zu 30,8 % von kleinen Säugern und nur zu 11,6 % von Fischen. Ebenfalls zum Nahrungsspektrum junger Krokodile gehören Amphibien und Reptilien, welche jedoch vergleichsweise selten erjagt werden.^[7]

Sozialverhalten und Fortpflanzung

Nilkrokodil

Nilkrokodil-Weibchen sind nicht territorial. Die Männchen bilden Reviere und verteidigen einen Uferabschnitt hartnäckig gegen andere Männchen. Sie schwimmen regelmäßig die Grenzen ihres Territoriums ab und vertreiben Eindringlinge. Gelegentlich kommt es zu Kämpfen.^[8]

Nilkrokodileier, Parc Djerba Explore, die Insel Djerba

Die Paarungszeit ist innerhalb des großen Verbreitungsgebiets sehr variabel. Wenn ein Männchen ein Weibchen trifft, hebt es seinen Schwanz und Kopf an und brüllt. Es schwimmt dem Weibchen entgegen, welches schließlich ebenfalls seinen Kopf anhebt und brüllt. Das Männchen legt zur Paarung seine Vorderbeine auf das Weibchen und steigt von der Seite auf ihren Rücken. Nach 5 Monaten legt das Weibchen dann 16–80 Eier, die 85–125 g wiegen. Der Zeitpunkt der Eiablage ist ebenso wie die Paarungszeit höchst variabel. In Tansania werden die Eier zum Beispiel im November gelegt, am Victoria-Nil und Albertsee Ende Dezember bis Anfang Januar, am Ruzizi zwischen April und August und auf Madagaskar von September bis Oktober. Das Weibchen gräbt mit seinen Hinterbeinen etwa 5–10 m vom Wasser entfernt ein 35–40 cm tiefes Erdloch, in welches die Eier gelegt werden. Das Loch wird anschließend zugedeckt und zusätzlich ein Nisthügel aus Substrat und Pflanzenresten aufgeschüttet. Während der Inkubation bewacht das Weibchen sein Nest vor Nesträubern wie etwa dem Nilwaran (Varanus niloticus), an den die Krokodile dennoch oft Eier verlieren. Nach 84–89 Tagen kündigen die Jungtiere in den Eiern mit froschartigen Lauten ihren Schlupf an. Das Weibchen gräbt dann das Nest wieder aus und trägt die Schlüpflinge in ihrem Maul ins Wasser. In den ersten Lebensmonaten bleiben die Jungtiere immer dicht bei ihrer Mutter, die sie bewacht. Auf sich nähernde Feinde macht die Mutter durch starke Körpervibrationen aufmerksam, worauf die Jungtiere sofort abtauchen. Jungtiere, die von der Gruppe abgesondert wurden oder angegriffen werden, stoßen einen Hilferuf aus, worauf das Weibchen sofort zum Jungtier eilt, um es zu verteidigen. Die Nacht verbringen die Jungtiere auf dem Rücken ihrer Mutter. Dennoch werden in den ersten Wochen oft mehr als 50 % der Jungtiere Opfer von Krabben, großen Fischen, Nilwaranen, Reihern, Störchen, Hyänen und Mungos.

Nilkrokodile und Menschen

Darstellung des ägyptischen Krokodilgotts Sobek in den Anlagen von Kom Ombo

Gefährdung

In der ersten Hälfte des 20. Jahrhunderts waren Nilkrokodile in ganz Afrika sehr häufig. In den folgenden Jahrzehnten sank der Bestand drastisch, da sie wegen ihrer Haut stark bejagt wurden. Krokodilleder wird zu zahlreichen Produkten wie Handtaschen, Gürteln etc. verarbeitet. Zusätzlichen Anreiz zur Jagd gaben Abschussprämien auf die Krokodile, da sie als Bedrohung für die Bevölkerung gesehen wurden. In den 1980er Jahren ging die Jagd aufgrund von Verboten zurück und Krokodilfarmen können heute den Bedarf der Lederindustrie decken. Auf diesen Farmen ist das Nilkrokodil eine der am häufigsten gehaltenen Arten.

Die Rote Liste gefährdeter Arten der IUCN führte das Nilkrokodil bis 1996 als gefährdet (vulnerable), inzwischen gilt die Art als nicht bedroht (least concern).^[9] Im Nil kommen die Tiere trotzdem kaum freilebend vor, sie leben in Naturschutzreservaten in breiten trägen Buchten.

Kulturelle Bezüge

Siehe Krokodile im alten Ägypten.

Bei Ausgrabungen von historischen Grabanlagen wurden auch mumifizierte Nilkrokodile gefunden. Im Jahr 2012 erhielten einige gut erhaltene Exemplare ein Museum an der Tempelanlage von Kom Ombo.^[10]

Dem Nilkrokodil sind einige Lieder gewidmet, beispielsweise Das Krokodil am Nil oder Krokodil Theophil und weitere.^[11][12]

Angriffe auf Menschen

Große Nilkrokodile können Menschen angreifen, die sich unvorsichtig in Krokodilgewässer begeben; Angriffe sind jedoch durch die enormen Bestandseinbrüche im 20. Jahrhundert weit seltener als früher geworden. Die meisten Zwischenfälle sind auf Übermut oder Unaufmerksamkeit der Opfer zurückzuführen.^[13] CrocBITE, die weltweite Datenbank für Krokodilangriffe der Charles Darwin University, registrierte bisher (Stand: Jan. 2014) 557 Attacken durch Nilkrokodile auf Menschen, 394 davon endeten für das Opfer tödlich. Nur vom Leistenkrokodil sind mehr Angriffe auf Menschen bekannt.^[14]

Zu Beginn des 21. Jahrhunderts ergeben sich verstärkt Konflikte zwischen Krokodilen und ansässigen Menschen, da einerseits die Bevölkerung rapide zunimmt, andererseits sich auch die Bestände der Krokodile erholen. Ebenso beklagt die lokale Bevölkerung, dass verstärkt Vieh gerissen wird und Fischernetze immer häufiger von Krokodilen beschädigt werden.

Literatur

• L. Trutnau & R. Sommerlad (2006): Krokodile. Biologie und Haltung. Edition Chimaira, Frankfurt am Main. ISBN 3-930612-96-8

Einzelnachweise

Crocodylus niloticus

Crocodylus niloticus

Aɣucaf n Nnil (assaɣ usnan: Crocodylus niloticus) d yiwen n uɣucaf meqqren (seld aɣucaf awlal) id yegran ur yengir ara, Yettidir ɣef yirawen n wasif n Nnil aladɣa deg tamiwin n uneẓul n Tefriqt adda n tneẓruft.

Aglam

Azal n tiddi n uɣucaf n Nnil yessawad gar n 4,5 m ar 5 m, Ma d azuk-is azal n 410 kg.

Učči

Tiwlafin

Crocodylus niloticus

Crocodylus niloticus

Ang buwaya ng Nilo (Crocodylus niloticus) ay isang buwaya sa Aprika, ang pinakamalaking freshwater predator sa Africa, at maaaring isaalang-alang ang pangalawang pinakamalaking nabubuhay na reptilya sa mundo, matapos ang buwaya sa dagat (Crocodylus porosus). Ang buwaya ng Nilo ay napakalawak sa buong Sub-Saharan Africa, na kadalasang nagaganap sa gitnang, silangan, at timog na rehiyon ng kontinente at nabubuhay sa iba't ibang uri ng mga nabubuhay na kapaligiran tulad ng mga lawa, ilog at marshlands.

Ang lathalaing ito ay isang usbong. Makatutulong ka sa Wikipedia sa nito.

Crocodylus niloticus es un specie de Crocodylus.

Crocodylus niloticus

The Nile crocodile (Crocodylus niloticus) is an African crocodile an mey be conseedered the seicont lairgest extant reptile in the warld, efter the sautwatter crocodile (Crocodylus porosus).^[2]

References

Nėla krakuodėlā

Nėla krakuodėls (luotīnėškā: Crocodylus niloticus) ī ruoplis, prėgolons prī krakuodėlu (Crocodylidae), dėdliausis ė pavuojingiausis vėsuo Afrėkuo. Paplėtė̄s vėsom žemīnė, skīros Sakaras dīkoma. Gīven opiū ėr ežerū pakronties. Ėlgoms lėgė 6 m, sonkoms lėgė 750 kg. Jied žėndoulius (tēpuogi gal' ožpoltė ėr žmuonis), ruoplius, žovis.

Crocodylus niloticus

Crocodylus niloticus

Ο Κροκόδειλος του Νείλου (επιστημονική ονομασία: Crocodylus niloticus - Κροκόδειλος ο νειλοτικός) είναι ένας κροκόδειλος ο οποίος απαντάται στην Αφρική, από την Σενεγάλη μέχρι την Αίγυπτο και την Νότια Αφρική, ενώ έχουν βρεθεί πληθυσμοί και στην Μαδαγασκάρη. Παλιότερα ζούσε και στο Δέλτα του Νείλου, αλλά σήμερα έχει εξαφανιστεί εκεί. Θεωρείται το δεύτερο μεγαλύτερο κροκοδείλιο που ζει σήμερα μετά τον θαλάσσιο κροκόδειλο, με μήκος που μπορεί να φτάσει μέχρι τα 5,5 μέτρα σε πολύ ηλικιωμένα ζώα και βάρος μέχρι 750 κιλά. Ο μεγαλύτερος που έχει μετρηθεί ήταν ένα αρσενικό στην Τανζανία μήκους 6,47 μέτρων και βάρος 1.090 κιλά.

Ετυμολογία

Το όνομα κροκόδειλος προέρχεται από την Αρχαία Ελλάδα, όπου σύμφωνα με τον Ηρόδοτο κροκόδριλος (από το κρόκος=κροκάλα=βότσαλο και δρίλος=σκουλήκι, άρα κρόκος+δρίλος=κροκόδριλος=το σκουλήκι που βγαίνει από τις πέτρες) ονομαζόταν το σημερινό κροκοδειλάκι ή κουρκουτά (Agama stellio). Πάντως, το μόνο κοινό ανάμεσα στον κροκόδειλο και την κουρκουτά είναι μόνο η κίνηση που κάνουν. Νειλοτικός σημαίνει αυτός που κατοικεί στο Νείλο. Άρα, κροκόδειλος ο Νειλοτικός λέγεται ο κροκόδειλος που κατοικεί στο Νείλο.

Ταξινόμηση

Ο κροκόδειλος του Νείλου κατατάσσεται στην τάξη των κροκοδειλίδων που περιλαμβάνει τρεις οικογένειες: την οικογένεια των αλλιγατορίδων στην οποία περιλαμβάνονται οι αλλιγάτορες και οι καϊμάν, στην οικογένεια των γαβιαλίδων που περιλαμβάνεται ο γαβιάλης του Γάγγη και στην οικογένεια των κροκοδειλίδων, στην οποία ανήκει ο κροκόδειλος του Νείλου. Οι κροκοδειλίδες υποδιαιρούνται σε 3 γένη: το Crocodylus, το Osteolaemus και στο Tomistoma. Ο κροκόδειλος του Νείλου ανήκει στο γένος Crocodylus, που εκτός από αυτόν περιλαμβάνει και τον κροκόδειλο της θάλασσας, τον κροκόδειλο του βούρκου και άλλα είδη.

Περιβάλλον και κατανομή

Ο κροκόδειλος του Νείλου συναντάται κατά μήκος των οχθών του Νείλου και σε όλη την υποσαχάρια Αφρική. Παλιά είχε μια ευρύτατη κατανομή παό το Ακρωτήριο της Καλής Ελπίδας ως την Παλαιστίνη. Σήμερα η κατανομή του είνια αρκετά περιορισμένη, στη Μαδαγασκάρη, την Τανζανία, τη Σενεγάλη την Αίγυπτο, το Σουδάν, το Κονγκό, την Κένυα και τη Νότια Αφρική. Τα δύο κύρια πάρκα στα οποία προστατεύεται είναι το Εθνικό Πάρκο της λίμνης Ροδόλφου στην Κένυα και στο Εθνικό Πάρκο του Μούρχισον στο Βικτωριανό Νείλο. Οι κροκόδειλοι του Νείλου κατοικούνε κυρίως σε αμμουδερές και χορταριασμένες όχθες ποταμών ή λιμνών, δεν αποκλείουν όμως και στην ανάγκη βραχώδεις όχθες ή και όχθες με χαλίκια. Καμιά φορά οι κροκόδειλοι του Νείλου πηγαίνουν κατά την περίοδο των βροχών μέσα στα έλη, τα ρυάκια και τις λιμνούλες που δημιουργούνται στα τροπικά δάση και ύστερα από την απόσυρση των νερών παγιδεύονται εκεί μέσα. Αν περάσει πολύς καιρός και παγιδευτούν στον πυθμένα της λίμνης ή του ποταμού, πέφτουν σε λήθαργο ωσότου να καλυτερέψει ο καιρός και να μπορέσουν να βγουν, όσοι όμως μπορούν μεταναστεύουν σε γειτονικό ποταμό ή λίμνη.

Περιγραφή

Ο κροκόδειλος του Νείλου έχει μήκος 5-7 μέτρα και είναι καλυμμένος εξ' ολοκλήρου με φολίδες οι οποίες είναι λείες στην κοιλιά, τετράγωνες και εύκαμπτες. Οι φολίδες της ράχης είναι τραχείες και σκληρές και θωρακίζουν στην κυριολεξία τα ερπετά. Οι κροκόδειλοι που ζουν σε κατηφορικά ποτάμια έχουν πιο σκληρό δέρμα ενώ οι κροκόδειλοι των λιμνών, των ήρεμων ποταμών και των βάλτων έχουν πιο μαλακό δέρμα.

Παραπομπές

Нил крокодилĕ

Crocodylus niloticus

Crocodylus niloticus

Нил крокодилĕ (лат. Crocodylus niloticus) — «шуса çӳрекенсен» ушкăнĕн чăн крокодилсен йышне кĕрекен пысăк чĕрчун.

Африкара пурăнакан крокодилсен виçĕ тĕсĕсенчен чи пысăкки.

Татах пăхăр

• Крокодилсем

Вуламалли

• Ананьева Н. Б., Боркин Л. Я., Даревский И. С., Орлов Н. Л. Пятиязычный словарь названий животных. Амфибии и рептилии. Латинский, русский, английский, немецкий, французский. / под общей редакцией акад. В. Е. Соколова. — М.: Рус. яз., 1988. — С. 139. — 10 500 экз. — ISBN 5-200-00232-X.
• Allen E. Greer. On the Maximum Total Length of the Salt-Water Crocodile (Crocodylus porosus) // Journal of Herpetology. — 1974. — Т. 8, № 4.
• Jamie Richard Oaks. Phylogenetic systematics, biogeography, and evolutionary ecology of the true crocodiles (Eusuchia: Crocodylidae: Crocodylus) // M.S. thesis, Louisiana State University. — 2007.
• Перейти к: 1 2 Nile crocodile. Энциклопедия Британника. Encyclopedia Britannica, Inc.. Проверено 2 ноября 2008. Архивировано 28 января 2012 года.

Каçăсем

• Нильский крокодил на zooclub.ru
• Культ животных в Древнем Египте
• Crocodylus niloticus(акăлч.)
• Охрана нильского крокодила(акăлч.)
• Крокодил-людоед, пойманый в Уганде(акăлч.)

Crocodylus niloticus

Crocodylus niloticus

Нилийн матар (Crocodylus niloticus) нь Африк тивийн Сомали, Этиоп, Кени, Замби улсын нутагт амьдардаг хэвлээр явагч юм.

Нилскиот крокодил (Crocodylus niloticus) е рептил од фамилијата Crocodylidae, кој ги населува повеќето региони во Африка (со исклучок на Северна Африка, Сејшели и Комори островите).

Просечната должина на ворасна индивидуа изнесува 4 метри, но забележани се и индивидуи кои надминуваат 7 метри како крокодилот од Бурунди наречен Густав.

Распространетост и живеалиште

Во антиката, нилските крокодили ја населувале делтата на реката Нил. Херодот запишал дека го населувале и езерото Моерис. Се смета дека изумреле во пределот на Сејшелите во почетокот на 19тиот век. Според пронајдените фосилни остатоци се знае дека го населувале и езерото Едвард. Нилискиот крокодил денес е распространет од реката Сенегал, езерото Чад и Судан до делтата на Окаванго. На Мадагаскар ги среќаваме во западните и јужните делови на островот. Повремено, овие животни се забележани и во Занзибар и на Комори ^[1].

Во западна Африка, нилскиот крокодил најчесто се сретнува во крајбрежните лагуни, делтите и во реките кои граничат со екваторијалниот шумски појас. Во источна Африка живеат во реки, езера, мочуришта и брани. Се случува понекогаш и да навлезат во океанот, па еден примерок во 1917та година бил забележан на 11 км од брегот на Санта Луција ^[1].

Карактеристики

Нилскиот крокодил има темно бронзена боја на грбот со црни точки, додека стомакот му е со темно жолта боја. Страните кои се со жолто-зелена нијанса имаат темни дамки кои се протегаат како коси пруги. Постои и варијација на бојата на кожата во зависност од живеалиштето. Така, крокодилите што живеат во реки со брз тек се со посветла боја на кожата од крокодилите кои престојуваат во езера или мочуришта. Овие крокодили имаат очи со зелена боја^[1], кои се заштитени со трепкачка ципа. Поседуваат и жлезди кои лачат солзи и го чистат окото.

Како и останатите крокодили и овие поседуваат четири кратки расчекорени нозе, долга опашка и моќни вилици. Кожата им е крекриена со крлушки и редови од коскени израстоци кои се протегаат во долж на нивниот грб и опашка.

Ноздрите, очите и ушите се наоѓаат на врвот на главата, што им овозможува додека го држат целото тело под вода, истовремено да слушаат и да ја гледаат околината. Младите крокодили имаат сива или кафеава боја со потемни пруги на телото и опашката. Како растат тие добиваат се потемна боја, а пругите, поготово оние на телото, исчезнуваат.

Овие крокодили најчесто лазат на стомак, но исто така можат и да одат со телото издигнато од земјата. Помалите индивидуи можат и да галопираат, а некои од поголемите крокодили можат да достигнат брзина и до 12-14 km/h. Овие животни се одлични пливачи, и пливаат со тоа што го мрдаат телото и опашката на синусоиден начин. Можат да пливаат подолго и со брзина од 30-35 km/h.

Нилскиот крокодил поседува срце со 4 комори, кое е доста ефикасно во оксидирање на крвта. Најчесто нуркаат само неколку минути, но доколку се во опасност можат да останат под вода и до 30 минути, а доколку не се движат можат да го задржат здивот и до 2 часа.

Силата на загризот на возрасен нилски крокодили измерена од страна на доктор Брејди Бар (Brady Barr) изнесува 22 kN. Сепак мускулите кои служат за отварање на вилицата се доста слаби, што му овозможува на човекот да ја држи затворена устата на крокодилот употребувајќи малку сила^[2]. Овие животи поседуваат помеѓу 64 и 68 заби. Младите крокодили поседуваат специфичен тврд кожен израсток на врвот на устата кој служи за кршење на лушпата на јајцето при нивното изведување, и кој брзо го снемува.

Големина

Споредување на големината на Нилскиот крокодил Crocodylus niloticus (просечен и најголемата регистрирана индивидуа) со човек.

Нилскиот крокодил е најголемото крокодиловидно животно во Африка и се смета за втор најголем крокодил после морскиот крокодил. Најчесто достигнуваат должина од 3,7 до 5 метри, но регистрирани се индивидуи и од 6 метри^[3]. Просечен мажјак тежи околу 545 килограми^[4], но во ретки случаи достигнуваат и до 909 килограми^[5]. Најголемиот мажјак нилски крокодил бил убиен во Танзанија и бил дол долг 6,45 метри и тежел околу 1090 килограми^[6]. Како и останатите крокодиловидни животни, и кај нилскиот крокодил постои полов диморфизам, така што мажјаците се за околу 30% поголеми од женките. Возрасните женки достигнуваат должина од 4 метри и тежат околу 300 килограми.

Постојат пријави за крокодили кои биле долги 7 метри, меѓутоа поради честото преценување на големината, постојат големи сомневања во веродостојноста на овие изјави. Најголемиот жив примерок се чини дека е човекојадниот нилски крокодил од Бурунди со име Густав, за кој се верува дека е долг 6 метри. Вакви џинови се ретки денес, но биле многу чести во минатото кога имало многу поголеми популации на крокодили, многу повеќе природно живеалиште и пред претераниот лов во 1940тите и 1950тите години.

Постојат одредени докази кои укажуваат на тоа дека нилските крокодили кои живеат на поладна клима, како во јужните делови на Африка, се помали и достигаат должина од само 4 метри. Постојат и џуџести нилски крокодили во Мали и во пустината Сахара кои растат само 2 до 3 метри во должина. Се претпоставува дека нивната големина се должи на лошите услови за живот а не на генетските предиспозиции.

Исхрана

Нилскиот крокодил е опортунистички суперпредатор кој го напаѓа било кое животно. Младите крокодили се доста мали, па затоа на почетокот се хранат со мал плен како инсекти и мали без’рбетници, а потоа брзо напредуваат кон водоземци, рептили и птици. Иако се суперпредатори, дури и на возрасните крокодили главна храна им претставуваат рибите и други мали рбетници. Сепак возрасните индивидуи преферираат поголем плен со цел да заштедат енергија. Нилските крокодили не пребираат многу во однос на исхраната, па напаѓаат скоро било кое животно кое доаѓа да пие вода на работ од реката^[7]. Најчест плен од цицачите се зебра, дива свиња, антилопа, коза, овца, гну и домашно говедо. Поголеми хербивори како жирафа или бафало се исто така плен повремено^[1]. Предатори како хиените, леопардите и други крокодили, вклучувајќи и индивидуи од истиот вид, се исто така регистрирани пленови на нилскиот крокодил. За крај, постои најмалку еден запис за група крокодили кои убиваат женка од Црн носорог во реката Тана во Кенија ^[1].

Возрасните нилски крокодили ги употребуваат телото и опашката за да ги насочат јатата риби кон плитак и потоа ги јадат со нагло завртување на главата. Крокодилите знаат и да соработуваат, односно тие се групираат и формираат полукруг во реката со што ги блокираат рибите кои мигрираат. Доминантниот мажјак секогаш јаде прв.

Пловер ги чисти забите на Нислки крокодил

Способноста да лежат скриени во вода, комбинирано со големата брзина на кратки дистанци, ги прави овие животни ефикасни опортунистички ловци на голем плен. Тие го зграбуваат пленот со моќните вилици, го одвлекуваат во вода и го држат под вода сè додека не се удави. Групи на крокодили можат да патуваат стотици метри во должина на реката за да се хранат со мрша.

Кога пленот е мртов тие го јадат со откинување на парчиња месо. Кога група на крокодили го дели убиениот плен, ја користат силата на загриз и на другите крокодили за да откинуваат поголеми парчиња месо. Тие загризуваат и потоа го превртуваат целото тело. Ова движење се нарекува и „смртоносно превртување“. Доколку крокодилот е сам, како поддршка може да користи и гранки или камења на кои го прикачуваат пленот.

Нилските крокодили се познати и по симбиотската врска со некои птици, како пловерот. Според одредени записи, крокодилот широко ја отвора устата, птицата влегува и ги чисти забите од малите парченца месо кои се заглавени меѓи нив. Ова сѐ уште е тешко да се докаже, и најверојатно не претставува вистинска симбиотска врска.

Размножување

Група на нилски крокодили

Мажјаците достигнуваат сексуална зрелост кога се долги околу 3 метри, додека женките кога се долги 2-2,5 метри. И на двата пола, за да ги достигнат овие должини им се потребни околу 10 години во нормални услови.

За време на сезоната за парење, мажјаците ги привлекуваат женките со рикање, плескање по водата со муцката, исфрлање вода низ носот како и испуштање на многу други звуци, кои сепак се многу помалку вокални од американсиот алигатор ^[1]. Според набљудувањата поголемите мажјаци се доста поуспешни во привлекување на женките. Женките ги несат јајцата околу 2 месеци после парењето.

Градењето гнездо се одвива во ноември или декември, односно за време на сувиот период во Северна Африка, и за време на дождовниот период во Јужна Африка. Најчесто гнездата ги градат на песочни брегови и пресушени речни текови. Женката копа дупка длабока 50тина сантиметри оддалечена неколку метри од брегот, во која положува од 25 до 80 јајца. Бројот на јајцата се разликува во различни популации, но во просек изнесува 50 јајца. Се случува повеќе женки да ги изградат гнездата многу блиску едни до други.

За разлика од останатите крокодили, кои гнездата ги прават од растенија, женката од нилски крокодил јајцата ги закопува во песок^[1]. Откако ќе ги закопа, идната мајка го чува гнездото за време на целиот период на инкубација кој трае 3 месеци. Идниот татко исто така останува во близина на гнездото, и заедно со мајката постојано напаѓаат доколку некој се доближи до јајцата. И покрај постојаната грижа на двајцата родители, гнездата многу често се уништувани од луѓето, гуштерите или некои други животни, за време кога мајката е на кратко отсутна.

Пред да излезат од јајцата, младите крокодили испуштаат пискави звуци кои се сигнал за мајката да го откопа гнездото. И мајката и таткото ги земаат јајцата во устата и ги тркалаат помеѓу јазикот и горниот дел од устата со што помагаат во кршењето на лушпата и излегувањето на младите. Кога ќе излезат од јајцата, мајката ги носи младите до водата.

Јајца од нилски крокодил

Одредувањето на полот на младите крокодили е зависен од температурата, што значи дека полот не е одреден генетски, туку во зависност од просечната температура за време на втората третина од периодот на инкубација. Ако температурата во гнездото е пониска од 31,7 °C или повисока од 34.5 °C, младите ќе бидат женски. Ако температурата е во рамките на овие степени, младите крокодили ќе бидат машки.

Младите крокодили се долги околи 30 сантиметри, и одприлика ја растат истата должина секоја година. Мајката се грижи за младите во следните две години, а доколку има повеќе гнезда во околината мајките формираат колонија каде сите заедно се грижат за своите и за младенчињата на другите женки. За ова време, мајката ги заштитува младите носејќи ги во својата уста или на нејзиниот грб.Младите крокодили не можат сами да се исхрануваат,и затоа ги храни нивната мајка.Додека не направат 2 години тие се сеуште мали за да се бранат и затоа не се одделуваат од својата мајка.Ако некое од малите крокодили умре не мајката го јаде.Кон крајот на втората година, младите крокодили веќе достигнуваат должина од 1,2 метри и го напуштаат регионот, но истовремено и ги избегнуваат териториите на поголемите и поворасните крокодили.

Должината на животниот век на крокодилите не е доволно познат, но се смета дека поголемите крокодили како Нилскиот живеат доста долго. Се претпоставува дека просечниот животен век изнесува помеѓу 70 и 100 години.

Заштитен статус

Од 1940тите до 1960тите, нилскиот крокодил е ловен најмногу поради неговата високо-квалитетна кожа, но исто така и поради неговото месо. Популацијата била драстично намалена, и видот се соочувал со изумирање. Националните закони и регулативите за тргување со крокодилска кожа, го спречиле ова изумирање и видот не е повеќе загрозен. Програмите за заштита на овие крокодили се всушност вештечки околини каде крокодилите живеат на сигурно и каде не се загрозени од ловци.

Се проценува дека има помеѓу 250 000 и 500 000 индивидуи во дивината. Нилскиот крокодил е доста распространет, со стабилни регистрирани популации во многу земји во источна Африка вклучувајќи ги Сомалија, Етиопија, Кенија и Замбија. Поради постојаната побарувачка на крокодилска кожа, постојат и фарми на крокодили. Во 1993 година, произведени се 80 000 крокодилски кожи, од кои повеќето се од крокодилските фарми во Зимбабве и Јужна Африка.

Ситуацијата е многу посериозна во централна и западна Африка, што сочинува околу две третини од живеалиштето на нилскиот крокодил. Крокодилските популации во овој регион се доста поретки и недоволно проучувани. Се смета дека природните популации се поретки поради лошите услови и компетицијата со африканскиот крокодил и џуџестиот крокодил. Дополнителни фактори се загубата на мочуриштата кои се природни живеалишта на овие животни како и ловењето во 1970тите години. Потребни се дополнителни програми за заштита за да се решат овие проблеми.

Нилскиот крокодил е суперпредатор во неговата околина, и е одговорен за регулирање на популациите на одредени видови на риби. Нилскиот крокодил се храни и со мртви животни кои доколку не се изедени можат да ја загадат водата. Најголемата опасност за нилскиот крокодил е човекот. Со заштитата ловокрадствотото веќе не претставува проблем, но затоа опасноста доаѓа од загадувањето на околината и сличајните заплеткувања во рибарските мрежи.

Како оправдување за ловот на овие крокодили се наведува опасноста за луѓето и е познат како голем човекојадец. За разлика од останатите човекојадни крокодили како морскиот крокодил, нилскиот живее во региони во близина на човечки популации, па затоа контактот со луѓе е многу почест. Иако нема сигурни бројки, се смета дека нилскиот крокодил убива неклоку стотици луѓе годишно, што е повеќе од сите други крокодили заедно^[8]. Некои проценуваат дека бројката на годишни жртви надминува и илјада^[9].

Заштитниот статус на Нилскиот крокодил од Црвената листа на IUCN од 1996 година спаѓа во видови со најмала загриженост од изумирање. Според листата на CITES овој крокодил спаѓа во Апендикс I (загрозен вид) во повеќето региони каде што е распространет, и во Апендикс II (незагрозен, но трговијата мора да биде контролирана).

Митови

Собек

статуа на нилски крокодил од стар египет

Луѓето од Стар Египет го обожувале Собек, крокодил-бог кој бил повржуван со плодноста, заштитата и моќта на фараонот. Собек бил насликуван како крокодил, како мумуфициран крокодил или како човек со глава од крокодил. Центар на неговото обожување било Средното Кралство, градот Арсиное, кај грцитe познат како Крокодополис.

Според Херодот, во 5тиот век п.н.е., некои еѓипјани чувале крокодили како домашни миленичиња. Во храмот на Собек кој се наоѓал во Арсиное, еден крокодил бил чуван во безенот во храмот, каде бил хранет, прекриван со накит и обожуван. Кога крокодилот умирал тој бил балсамиран, мумифициран, ставан во саркофаг и потоа закопуван во света гробница. Многу мумифицирани крокодили па дури и крокодилски јајца се пронајдени во египетските гробници.

Во Стар Египет биле употребувани магии за да се смират крокодилите, па дури и во денешно време, нубијските рибари закачуваат крокодили над праговите за да ги заштитат од зло.

Етимологија

Биномното име Crocodylus niloticus е добиено од грчкиот збор kroko („камен“), deilos („црв“ или „човек“), што се однесува на неговата специфична кожа, и niloticus, што значи „од реката Нил“.

Наводи

நைல் முதலை

Crocodylus niloticus

Crocodylus niloticus

நைல் முதலை (விலங்கியல் பெயர்:குரோக்கோடைலஸ் நைலோட்டிகஸ்) ஆப்பிரிக்காவில் காணப்படும் மூன்று முதலைச் சிற்றினங்களில்(species) ஒன்றாகும். மேலும் இவை முதலைச் சிற்றினங்களிலேயே இரண்டாவது பெரியதும் ஆகும். நைல் முதலைகள் ஏறக்குறைய ஆப்பிரிக்கா முழுதும் சகாராவின் தென்பகுதியிலும் மடகாஸ்கர் தீவிலும் காணப்படுகின்றன.

மேலும் பார்க்க

• முதலை

மேற்கோள்கள்

1. ↑ "Crocodylus niloticus". பன்னாட்டு இயற்கைப் பாதுகாப்புச் சங்கத்தின் செம்பட்டியல் பதிப்பு 2011.1. பன்னாட்டு இயற்கைப் பாதுகாப்புச் சங்கம் (1996). பார்த்த நாள் 12 May 2006.

Nkɔli míbalé

Crocodylus niloticus

Crocodylus niloticus

Nkɔli (latɛ́ : Crocodylus niloticus) ezalí nyama o libóta lya nyóka ya nzelá ya mái. Ezalí ngandó eye elíyaka bato mpé nyama isúsu, evándaka o mái ya ebale tǒ ya molúká, ekokí kobima o mokili na makáká ma mikúsé ma yangó. Ezalí na monɔkɔ ya molaí .

Tálá mpé

• Ngandó

Crocodylus niloticus

Crocodylus niloticus

Ọ̀ni Nílò (Crocodylus niloticus) je iru ọ̀ni ti Afrika to wopo si Somalia, Ethiopia, Uganda, Kenya, Egypt, Zambia and Zimbabwe.

Itokasi

The Nile crocodile (Crocodylus niloticus) is a large crocodilian native to freshwater habitats in Africa, where it is present in 26 countries. It is widely distributed throughout sub-Saharan Africa, occurring mostly in the central, eastern, and southern regions of the continent, and lives in different types of aquatic environments such as lakes, rivers, swamps, and marshlands.^[4] In West Africa, it occurs along with two other crocodilians.^[5] Although capable of living in saline environments, this species is rarely found in saltwater, but occasionally inhabits deltas and brackish lakes. The range of this species once stretched northward throughout the Nile, as far north as the Nile Delta. Generally, the adult male Nile crocodile is between 3.5 and 5 m (11 ft 6 in and 16 ft 5 in) in length and weighs 225 to 750 kg (500 to 1,650 lb).^[6][7] However, specimens exceeding 6.1 m (20 ft) in length and 1,000 kg (2,200 lb) in weight have been recorded.^[8] It is the largest freshwater predator in Africa, and may be considered the second-largest extant reptile in the world, after the saltwater crocodile (Crocodylus porosus).^[9][10] Size is sexually dimorphic, with females usually about 30% smaller than males. The crocodile has thick, scaly, heavily armoured skin.

Nile crocodiles are opportunistic apex predators; a very aggressive crocodile, they are capable of taking almost any animal within their range. They are generalists, taking a variety of prey.^[11][10] Their diet consists mostly of different species of fish, reptiles, birds, and mammals. They are ambush predators that can wait for hours, days, and even weeks for the suitable moment to attack. They are agile predators and wait for the opportunity for a prey item to come well within attack range. Even swift prey are not immune to attack. Like other crocodiles, Nile crocodiles have a powerful bite that is unique among all animals, and sharp, conical teeth that sink into flesh, allowing a grip that is almost impossible to loosen. They can apply high force for extended periods of time, a great advantage for holding down large prey underwater to drown.^[10]

Nile crocodiles are relatively social.^[12] They share basking spots and large food sources, such as schools of fish and big carcasses. Their strict hierarchy is determined by size. Large, old males are at the top of this hierarchy and have first access to food and the best basking spots. Crocodiles tend to respect this order; when it is infringed, the results are often violent and sometimes fatal.^[13] Like most other reptiles, Nile crocodiles lay eggs; these are guarded by the females and males, making the Nile crocodiles one of few reptile species whose males contribute to parental care.^[14] The hatchlings are also protected for a period of time, but hunt by themselves and are not fed by the parents.^[11][15]

The Nile crocodile is one of the most dangerous species of crocodile and is responsible for hundreds of human deaths every year.^[16] It is common and is not endangered, despite some regional declines or extirpations.

Etymology and naming

The binomial name Crocodylus niloticus is derived from the Greek κρόκη, kroke ("pebble"), δρῖλος, drilos ("worm"), referring to its rough skin; and niloticus, meaning "from the Nile River". The Nile crocodile is called^[17] timsah al-nil in Arabic, mamba in Swahili, garwe in Shona, ngwenya in Ndebele, ngwena in Venda, kwena in Sotho and Tswana, and tanin ha-yeor in Hebrew. It also sometimes referred to as the African crocodile, Ethiopian crocodile, and common crocodile.^[18][10][19]

Taxonomy

Although no subspecies are currently formally recognized, as many as seven have been proposed, mostly due to variations in appearance and size noted in various populations throughout Africa. These have consisted of C. n. africanus (informally named the East African Nile crocodile), C. n. chamses (the West African Nile crocodile), C. n. cowiei (the South African Nile crocodile), C. n. madagascariensis (the Malagasy or Madagascar Nile crocodile, regionally also known as the croco Mada, which translates to Malagasy crocodile), C. n. niloticus (the Ethiopian Nile crocodile; this would be the nominate subspecies), C. n. pauciscutatus (the Kenyan Nile crocodile) and C. (n.) suchus (now widely considered a separate species).^[20][21]

In a study of the morphology of the various populations, including C. (n.) suchus, the appearance of the Nile crocodile sensu lato was found to be more variable than that of any other currently recognized crocodile species, and at least some of these variations were related to locality.^[22] For example, a study on Lake Turkana in Kenya (informally this population would be placed in C. n. pauciscutatus) found that the local crocodiles have more osteoderms in their ventral surface than other known populations, and thus are of lesser value in leather trading, accounting for an exceptionally large (possibly overpopulated) local population there in the late 20th century.^[23] The segregation of the West African crocodile (C. suchus) from the Nile crocodile has been supported by morphological characteristics,^[22][24] studies of genetic materials^[21][24] and habitat preferences.^[25] The separation of the two is not recognized by the IUCN as their last evaluations of the group was in 2008 and 2009,^[2][26] years before the primary publications supporting the distinctiveness of the West African crocodiles.^[22][24][25]

Evolution

Although originally thought to be the same species as the West African crocodile, genetic studies using DNA sequencing have revealed that the Nile crocodile is actually more closely related to the crocodiles of the Americas, namely the American (C. acutus), Cuban (C. rhombifer), Morelet's (C. moreletii), and Orinoco crocodiles (C. intermedius).^{[24][27][28][29][30][31]} The fossil species C. checchiai from the Miocene in Kenya was about the same size as the modern Nile crocodiles and shared similar physical characteristics to the modern species,^[27][28][32] and analysis of C. checchiai supports their close relationship and the theory of the Nile crocodile being the base of the evolutionary radiation of the New World crocodiles.^[33] Dispersal across the Atlantic from Africa is thought to have occurred 5 to 6 million years ago.^[34][35]

At one time, the fossil species Rimasuchus lloydi was thought to be the ancestor of the Nile crocodile, but more recent research has indicated that Rimasuchus, despite its very large size (about 20–30% bigger than a Nile crocodile with a skull length estimated up to 97 cm (38 in)), is more closely related to the dwarf crocodile (Osteolaemus tetraspis) among living species.^[23][27] Two other fossil species from Africa retained in the genus Crocodylus appear to be closely related to the Nile crocodile: C. anthropophagus from Plio-Pleistocene Tanzania and C. thorbjarnarsoni from Plio-Pleistocene Kenya. C. anthropophagus and C. thorbjarnarsoni were both somewhat larger, with projected total lengths up to 7.5–7.6 m (24 ft 7 in – 24 ft 11 in).^[27][28][32] As well as being larger, C. anthropophagus and C. thorbjarnarsoni, as well as Rimasuchus spp., were all relatively broad-snouted, indicating a specialization at hunting sizeable prey, such as large mammals and freshwater turtles, the latter much larger than any in present-day Africa.^[27][28] Studies have since shown these other African crocodiles to be only more distantly related to the Nile crocodile.^[30][31]

Below is a cladogram based on a 2018 tip dating study by Lee & Yates simultaneously using morphological, molecular (DNA sequencing), and stratigraphic (fossil age) data,^[30] as revised by the 2021 Hekkala et al. paleogenomics study using DNA extracted from the extinct Voay.^[31]

Voay†

Crocodylus anthropophagus†

Crocodylus thorbjarnarsoni†

Crocodylus palaeindicus†

Crocodylus Tirari Desert†

Crocodylus johnstoni Freshwater crocodile

Crocodylus novaeguineae New Guinea crocodile

Crocodylus mindorensis Philippine crocodile

Crocodylus porosus Saltwater crocodile

Crocodylus siamensis Siamese crocodile

Crocodylus palustris Mugger crocodile

Crocodylus checchiai†

Crocodylus falconensis†

Crocodylus suchus West African crocodile

Crocodylus niloticus Nile crocodile

Crocodylus moreletii Morelet's crocodile

Crocodylus rhombifer Cuban crocodile

Crocodylus intermedius Orinoco crocodile

Crocodylus acutus American crocodile

Characteristics and physiology

Side view in South Africa

Adult Nile crocodiles have a dark bronze colouration above, with faded blackish spots and stripes variably appearing across the back and a dingy off-yellow on the belly, although mud can often obscure the crocodile's actual colour.^[19] The flanks, which are yellowish-green in colour, have dark patches arranged in oblique stripes in highly variable patterns. Some variation occurs relative to environment; specimens from swift-flowing waters tend to be lighter in colour than those dwelling in murkier lakes or swamps, which provides camouflage that suits their environment, an example of clinal variation. Nile crocodiles have green eyes.^[10] The colouration also helps to camouflage them; juveniles are grey, multicoloured, or brown, with dark cross-bands on the tail and body.^[36] The underbelly of young crocodiles is yellowish green. As they mature, Nile crocodiles become darker and the cross-bands fade, especially those on the upper-body. A similar tendency in coloration change during maturation has been noted in most crocodile species.^[20][37]

Most morphological attributes of Nile crocodiles are typical of crocodilians as a whole. Like all crocodilians, for example, the Nile crocodile is a quadruped with four short, splayed legs, a long, powerful tail, a scaly hide with rows of ossified scutes running down its back and tail, and powerful, elongated jaws.^[36][38] Their skin has a number of poorly understood integumentary sense organs that may react to changes in water pressure, presumably allowing them to track prey movements in the water.^[39] The Nile crocodile has fewer osteoderms on the belly, which are much more conspicuous on some of the more modestly sized crocodilians. The species, however, also has small, oval osteoderms on the sides of the body, as well as the throat.^[37][40] The Nile crocodile shares with all crocodilians a nictitating membrane to protect the eyes and lachrymal glands to cleanse its eyes with tears. The nostrils, eyes, and ears are situated on the top of the head, so the rest of the body can remain concealed under water.^[38][41] They have a four-chambered heart, although modified for their ectothermic nature due to an elongated cardiac septum, physiologically similar to the heart of a bird, which is especially efficient at oxygenating their blood.^[42][43] As in all crocodilians, Nile crocodiles have exceptionally high levels of lactic acid in their blood, which allows them to sit motionless in water for up to 2 hours. Levels of lactic acid as high as they are in a crocodile would kill most vertebrates.^[20] However, exertion by crocodilians can lead to death due to increasing lactic acid to lethal levels, which in turn leads to failure of the animal's internal organs. This is rarely recorded in wild crocodiles, normally having been observed in cases where humans have mishandled crocodiles and put them through overly extended periods of physical struggling and stress.^[12][23]

Nile crocodile's head

Skull and head morphology

Details of the skull from a juvenile Nile crocodile

Naturalized crocodile head.

The mouths of Nile crocodiles are filled with 64 to 68 sharply pointed, cone-shaped teeth (about a dozen less than alligators have). For most of a crocodile's life, broken teeth can be replaced. On each side of the mouth, five teeth are in the front of the upper jaw (premaxilla), 13 or 14 are in the rest of the upper jaw (maxilla), and 14 or 15 are on either side of the lower jaw (mandible). The enlarged fourth lower tooth fits into the notch on the upper jaw and is visible when the jaws are closed, as is the case with all true crocodiles.^[12][38] Hatchlings quickly lose a hardened piece of skin on the top of their mouths called the egg tooth, which they use to break through their eggshells at hatching. Among crocodilians, the Nile crocodile possesses a relatively long snout, which is about 1.6 to 2.0 times as long as broad at the level of the front corners of the eyes.^[44] As is the saltwater crocodile, the Nile crocodile is considered a species with medium-width snout relative to other extant crocodilian species.^[5]

In a search for the largest crocodilian skulls in museums, the largest verifiable Nile crocodile skulls found were several housed in Arba Minch, Ethiopia, sourced from nearby Lake Chamo, which apparently included several specimens with a skull length more than 65 cm (26 in), with the largest one being 68.6 cm (27.0 in) in length with a mandibular length of 87 cm (34 in). Nile crocodiles with skulls this size are likely to measure in the range of 5.4 to 5.6 m (17 ft 9 in to 18 ft 4 in), which is also the length of the animals according to the museum where they were found. However, larger skulls may exist, as this study largely focused on crocodilians from Asia.^[10][45] The detached head of an exceptionally large Nile crocodile (killed in 1968 and measuring 5.87 m (19 ft 3 in) in length) was found to have weighed 166 kg (366 lb), including the large tendons used to shut the jaw.^[9]

Biting force

The bite force exerted by an adult Nile crocodile has been shown by Brady Barr to measure 22 kN (5,000 lbf). However, the muscles responsible for opening the mouth are exceptionally weak, allowing a person to easily hold them shut, and even larger crocodiles can be brought under control by the use of duct tape to bind the jaws together.^[46] The broadest snouted modern crocodilians are alligators and larger caimans. For example, a 3.9 m (12 ft 10 in) black caiman (Melanosuchus niger) was found to have a notably broader and heavier skull than that of a Nile crocodile measuring 4.8 m (15 ft 9 in).^[47] However, despite their robust skulls, alligators and caimans appear to be proportionately equal in biting force to true crocodiles, as the muscular tendons used to shut the jaws are similar in proportional size. Only the gharial (Gavialis gangeticus) (and perhaps some of the few very thin-snouted crocodilians) is likely to have noticeably diminished bite force compared to other living species due to its exceptionally narrow, fragile snout. More or less, the size of the tendons used to impart bite force increases with body size and the larger the crocodilian gets, the stronger its bite is likely to be. Therefore, a male saltwater crocodile, which had attained a length around 4.59 m (15 ft 1 in), was found to have the most powerful biting force ever tested in a lab setting for any type of animal.^[48][49]

Size

Healthy subadult

A large Nile crocodile in Entebbe

The Nile crocodile is the largest crocodilian in Africa, and is generally considered the second-largest crocodilian after the saltwater crocodile.^[10] Typical size has been reported to be as much as 4.5 to 5.5 m (14 ft 9 in to 18 ft 1 in), but this is excessive for actual average size per most studies and represents the upper limit of sizes attained by the largest animals in a majority of populations.^[11][36][37] Alexander and Marais (2007) give the typical mature size as 2.8 to 3.5 m (9 ft 2 in to 11 ft 6 in); Garrick and Lang (1977) put it at from 3.0 to 4.5 m (9 ft 10 in to 14 ft 9 in).^[50][9][13] According to Cott (1961), the average length and weight of Nile crocodiles from Uganda and Zambia in breeding maturity was 3.16 m (10 ft 4 in) and 137.5 kg (303 lb).^[11] Per Graham (1968), the average length and weight of a large sample of adult crocodiles from Lake Turkana (formerly known as Lake Rudolf), Kenya was 3.66 m (12 ft 0 in) and body mass of 201.6 kg (444 lb).^[51] Similarly, adult crocodiles from Kruger National Park reportedly average 3.65 m (12 ft 0 in) in length.^[10] In comparison, the saltwater crocodile and gharial reportedly both average around 4 m (13 ft 1 in), so are about 30 cm (12 in) longer on average, and the false gharial (Tomistoma schlegelii) may average about 3.75 m (12 ft 4 in), so may be slightly longer, as well. However, compared to the narrow-snouted, streamlined gharial and false gharial, the Nile crocodile is more robust and ranks second to the saltwater crocodile in total average body mass among living crocodilians, and is considered to be the second-largest extant reptile.^{[9][51][10][37]} The largest accurately measured male, shot near Mwanza, Tanzania, measured 6.45 m (21 ft 2 in) and weighed about 1,043–1,089 kg (2,300–2,400 lb).^[9] Another large male measuring 5.8 m (19 ft 0 in) in total length (Cott 1961) was among the largest Nile crocodiles ever recorded. It was estimated to weigh 1,082 kg (2,385 lb).^[52]

Size and sexual dimorphism

Groupings of crocodiles like this can include crocodiles of various sizes, but seldom of less than 2 m (6 ft 7 in), lest a cannibalistic large specimen launch an attack.

Like all crocodiles, they are sexually dimorphic, with the males up to 30% larger than the females, though the difference is considerably less compared to some species, like the saltwater crocodile. Male Nile crocodiles are about 30 to 50 cm (12 to 20 in) longer on average at sexual maturity and grow more so than females after becoming sexually mature, especially expanding in bulk after exceeding 4 m (13 ft 1 in) in length.^[36][53] Adult male Nile crocodiles usually range in length from 3.3 to 5.0 m (10 ft 10 in to 16 ft 5 in) long; at these lengths, an average sized male may weigh from 150 to 750 kg (330 to 1,650 lb).^{[11][51][54][55][56]} Very old, mature ones can grow to 5.5 m (18 ft 1 in) or more in length (all specimens over 5.5 m (18 ft 1 in) from 1900 onward are cataloged later).^[9][10][57] Large mature males can reach 1,000 kg (2,200 lb) or more in weight.^[58] Mature female Nile crocodiles typically measure 2.2 to 3.8 m (7 ft 3 in to 12 ft 6 in), at which lengths the average female specimen would weigh 40 to 250 kg (88 to 551 lb).^{[11][51][36][59]}

An old male individual, named "Big Daddy", housed at Mamba Village Centre, Mombasa, Kenya is considered to be one of the largest living Nile crocodiles in captivity. It measures 5 m (16 ft 5 in) in length and weighs 800 kg (1,800 lb). In 2007, at the Katavi National Park, Brady Barr captured a specimen measuring 5.36 m (17 ft 7 in) in total length (with a considerable portion of its tail tip missing). The weight of this specimen was estimated to be 838 kg (1,847 lb), making it one of the largest crocodiles ever to be captured and released alive.^[52] The bulk and mass of individual crocodiles can be fairly variable, some animals being relatively slender, while others being very robust; females are often bulkier than males of a similar length.^[11][10] As an example of the body mass increase undergone by mature crocodiles, one of the larger crocodiles handled firsthand by Cott (1961) was 4.4 m (14 ft 5 in) and weighed 414.5 kg (914 lb), while the largest specimen measured by Graham and Beard (1973) was 4.8 m (15 ft 9 in) and weighed more than 680 kg (1,500 lb).^[11][9][60] One of the largest known specimens from South Africa, caught by J.G Kuhlmann in Venda, which was 5.5 m (18 ft 1 in) long weighed 905.7 kg (1,997 lb).^[61] On the other hand, another individual measuring 5.87 m (19 ft 3 in) in length was estimated to weigh between 770–820 kg (1,700–1,800 lb).^[62] In attempts to parse the mean male and female lengths across the species, the mean adult length was estimated to be reportedly 4 m (13 ft 1 in) in males, at which males would average about 280 kg (620 lb) in weight, while that of the female is 3.05 m (10 ft 0 in), at which females would average about 116 kg (256 lb).^{[11][51][63][64]} This gives the Nile crocodile somewhat of a size advantage over the next largest non-marine predator on the African continent, the lion (Panthera leo), which averages 188 kg (414 lb) in males and 124 kg (273 lb) in females, and attains a maximum known weight of 313 kg (690 lb), far less than that of large male crocodiles.^[9][65]

Nile crocodiles from cooler climates, like the southern tip of Africa, may be smaller, reaching maximum lengths of only 4 m (13 ft 1 in). A crocodile population from Mali, the Sahara Desert, and elsewhere in West Africa reaches only 2 to 3 m (6 ft 7 in to 9 ft 10 in) in length,^[66] but it is now largely recognized as a separate species, the West African crocodile.^[24]

Distribution and habitat

The Nile crocodile is presently the most common crocodilian in Africa, and is distributed throughout much of the continent. Among crocodilians today, only the saltwater crocodile occurs over a broader geographic area,^[67] although other species, especially the spectacled caiman (Caiman crocodilus) (due to its small size and extreme adaptability in habitat and flexibility in diet), seem to actually be more abundant.^[68] This species’ historic range, however, was even wider. They were found as far north as the Mediterranean coast in the Nile Delta and across the Red Sea in Israel, Palestine and Syria. The Nile crocodile has historically been recorded in areas where they are now regionally extinct. For example, Herodotus recorded the species inhabiting Lake Moeris in Egypt. They are thought to have become extinct in the Seychelles in the early 19th century (1810–1820).^[10][36] Today, Nile crocodiles are widely found in, among others, Somalia, Ethiopia, Uganda,^[69] Kenya, Egypt, the Central African Republic, the Democratic Republic of the Congo, Equatorial Guinea, Tanzania, Rwanda, Burundi, Zambia, Zimbabwe, Gabon, Angola, South Africa, Malawi, Mozambique, Namibia, Sudan, South Sudan, Botswana, and Cameroon.^[26] The Nile crocodile's current range of distribution extends from the regional tributaries of the Nile in Sudan and Lake Nasser in Egypt to the Cunene river of Angola, the Okavango Delta of Botswana, and the Olifants river in South Africa.^[70]

Isolated populations also exist in Madagascar, which likely colonized the island after the extinction of the endemic crocodile Voay.^[71][72] In Madagascar, crocodiles occur in the western and southern parts from Sambirano to Tôlanaro. They have been spotted in Zanzibar and the Comoros in modern times, but occur very rarely.^[10]

The species was previously thought to extend in range into the whole of West and Central Africa,^[73][74] but these populations are now typically recognized as a distinct species, the West African (or desert) crocodile.^[24] The distributional boundaries between these species were poorly understood, but following several studies, they are now better known. West African crocodiles are found throughout much of West and Central Africa, ranging east to South Sudan and Uganda where the species may come into contact with the Nile crocodile. Nile crocodiles are absent from most of West and Central Africa, but range into the latter region in eastern and southern Democratic Republic of Congo, and along the Central African coastal Atlantic region (as far north to Cameroon).^[24][75] Likely a level of habitat segregation occurs between the two species, but this remains to be confirmed.^[25][76]

Nile crocodiles may be able to tolerate an extremely broad range of habitat types, including small brackish streams, fast-flowing rivers, swamps, dams, and tidal lakes and estuaries.^[53] In East Africa, they are found mostly in rivers, lakes, marshes, and dams, favoring open, broad bodies of water over smaller ones. They are often found in waters adjacent to various open habitats such as savanna or even semi-desert but can also acclimate to well-wooded swamps, extensively wooded riparian zones, waterways of other woodlands and the perimeter of forests.^[77][78][79] In Madagascar, the remnant population of Nile crocodiles has adapted to living within caves.^[10] Nile crocodiles may make use of ephemeral watering holes on occasion.^[80] Although not a regular sea-going species as is the American crocodile, and especially the saltwater crocodile, the Nile crocodile possesses salt glands like all true crocodiles (i.e., excluding alligators and caimans), and does on occasion enter coastal and even marine waters.^[81] They have been known to enter the sea in some areas, with one specimen having been recorded 11 km (6.8 mi) off St. Lucia Bay in 1917.^[11][82]

Invasive potential

Nile crocodiles have been recently captured in South Florida, though no signs that the population is reproducing in the wild have been found.^[83] Genetic studies of Nile crocodiles captured in the wild in Florida have revealed that the specimens are all closely related to each other, suggesting a single source of the introduction. This source remains unclear, as their genetics do not match samples collected from captives at various zoos and theme parks in Florida. When compared to Nile crocodiles from their native Africa, the Florida wild specimens are most closely related to South African Nile crocodiles.^[84] It is unknown how many Nile crocodiles are currently at large in Florida.^[85][86] The animals likely were either brought there to be released or are escapees.^[87]

Behaviour

Adult Nile crocodile basking at Victoria Nile of Murchison Falls National Park, Uganda

Generally, Nile crocodiles are relatively inert creatures, as are most crocodilians and other large, cold-blooded creatures. More than half of the crocodiles observed by Cott (1961), if not disturbed, spent the hours from 9:00 a.m. to 4:00 p.m. continuously basking with their jaws open if conditions were sunny. If their jaws are bound together in the extreme midday heat, Nile crocodiles may easily die from overheating.^[11][88] Although they can remain practically motionless for hours on end, whether basking or sitting in shallows, Nile crocodiles are said to be constantly aware of their surroundings and aware of the presence of other animals.^[10] However, mouth-gaping (while essential to thermoregulation) may also serve as a threat display to other crocodiles. For example, some specimens have been observed mouth-gaping at night, when overheating is not a risk.^[15] In Lake Turkana, crocodiles rarely bask at all through the day, unlike crocodiles from most other areas, for unknown reasons, usually sitting motionless partially exposed at the surface in shallows, with no apparent ill effects from the lack of basking on land.^[60]

Crocodiles are deft and agile swimmers when motivated.

In South Africa, Nile crocodiles are more easily observed in winter because of the extensive amount of time they spend basking at this time of year. More time is spent in water on overcast, rainy, or misty days.^[89] In the southern reaches of their range, as a response to dry, cool conditions that they cannot survive externally, crocodiles may dig and take refuge in tunnels and engage in aestivation.^[36] Pooley found in Royal Natal National Park that during aestivation, young crocodiles of 60 to 90 cm (24 to 35 in) total length would dig tunnels around 1.2 to 1.8 m (3 ft 11 in to 5 ft 11 in) in depth for most, with some tunnels measuring more than 2.7 m (8 ft 10 in), the longest there being 3.65 m (12 ft 0 in). Crocodiles in aestivation are lethargic, entering a state similar to animals that hibernate. Only the largest individuals engaging in aestivation leave the burrow to sun on the warmest days; otherwise, these crocodiles rarely left their burrows. Aestivation has been recorded from May to August.^[10][36]

Nile crocodiles usually dive for only a few minutes at a time, but can swim under water up to 30 minutes if threatened. If they remain fully inactive, they can hold their breath for up to 2 hours (which, as aforementioned, is due to the high levels of lactic acid in their blood).^[20] They have a rich vocal range and good hearing. Nile crocodiles normally crawl along on their bellies, but they can also "high walk" with their trunks raised above the ground. Smaller specimens can gallop, and even larger individuals are capable of occasional, surprising bursts of speed, briefly reaching up to 14 km/h (8.7 mph).^[11][90] They can swim much faster, moving their bodies and tails in a sinuous fashion, and they can sustain this form of movement much longer than on land, with a maximum known swimming speed of 30 to 35 km/h (19 to 22 mph), more than three times faster than any human.^[91]

Drawing depicting the mythical relationship between plovers and crocodiles – no reliable observations exist of this purported symbiosis

Nile crocodiles have been widely known to have gastroliths in their stomachs, which are stones swallowed by animals for various purposes. Although this is clearly a deliberate behaviour for the species, the purpose is not definitively known. Gastroliths are not present in hatchlings, but increase quickly in presence within most crocodiles examined at 2–3.1 m (6 ft 7 in – 10 ft 2 in) and yet normally become extremely rare again in very large specimens, meaning that some animals may eventually expel them.^[11][10] However, large specimens can have a large number of gastroliths. One crocodile measuring 3.84 m (12 ft 7 in) and weighing 239 kg (527 lb) had 5.1 kg (11 lb) of stones in its stomach, perhaps a record gastrolith weight for a crocodile.^[11] Specimens shot near Mpondwe on the Semliki River had gastroliths in their stomach despite being shot miles away from any sources for the stones; the same holds true for specimens from Kafue Flats, Upper Zambesi and Bangweulu Swamp, all of which often had stones inside them despite being nowhere near stony regions. Cott (1961) felt that gastroliths were most likely serving as ballast to provide stability and additional weight to sink in water, this bearing great probability over the theories that they assist in digestion and staving off hunger.^[11][10] However, Alderton (1998) stated that a study using radiology found that gastroliths were seen to internally aid the grinding of food during digestion for a small Nile crocodile.^[23]

Herodotus claimed that Nile crocodiles have a symbiotic relationship with certain birds, such as the Egyptian plover (Pluvianus aegyptius), which enter the crocodile's mouth and pick leeches feeding on the crocodile's blood, but no evidence of this interaction actually occurring in any crocodile species has been found, and it is most likely mythical or allegorical fiction.^[92] However, Guggisberg (1972) had seen examples of birds picking scraps of meat from the teeth of basking crocodiles (without entering the mouth) and prey from soil very near basking crocodiles, so felt it was not impossible that a bold, hungry bird may occasionally nearly enter a crocodile's mouth, but not likely as a habitual behaviour.^[10]

Hunting and diet

Attacking a Burchell's zebra in Kruger National Park, South Africa

Nile crocodiles are apex predators throughout their range. In the water, this species is an agile and rapid hunter relying on both movement and pressure sensors to catch any prey unfortunate enough to present itself inside or near the waterfront.^[93] Out of water, however, the Nile crocodile can only rely on its limbs, as it gallops on solid ground, to chase prey.^[94] No matter where they attack prey, this and other crocodilians take practically all of their food by ambush, needing to grab their prey in a matter of seconds to succeed.^[10] They have an ectothermic metabolism, so can survive for long periods between meals. However, for such large animals, their stomachs are relatively small, not much larger than a basketball in an average-sized adult, so as a rule, they are anything but voracious eaters.^[12] Young crocodiles feed more actively than their elders, according to studies in Uganda and Zambia. In general, at the smallest sizes (0.3–1 m (1 ft 0 in – 3 ft 3 in)), Nile crocodiles were most likely to have full stomachs (17.4% full per Cott); adults at 3–4 m (9 ft 10 in – 13 ft 1 in) in length were most likely to have empty stomachs (20.2%). In the largest size range studied by Cott, 4–5 m (13 ft 1 in – 16 ft 5 in), they were the second most likely to either have full stomachs (10%) or empty stomachs (20%).^[11] Other studies have also shown a large number of adult Nile crocodiles with empty stomachs. For example, in Lake Turkana, Kenya, 48.4% of crocodiles had empty stomachs.^[51] The stomachs of brooding females are always empty, meaning that they can survive several months without food.^[10]

The Nile crocodile mostly hunts within the confines of waterways, attacking aquatic prey or terrestrial animals when they come to the water to drink or to cross.^[36] The crocodile mainly hunts land animals by almost fully submerging its body under water. Occasionally, a crocodile quietly surfaces so that only its eyes (to check positioning) and nostrils are visible, and swims quietly and stealthily toward its mark. The attack is sudden and unpredictable. The crocodile lunges its body out of water and grasps its prey. On other occasions, more of its head and upper body is visible, especially when the terrestrial prey animal is on higher ground, to get a sense of the direction of the prey item at the top of an embankment or on a tree branch.^[10] Crocodile teeth are not used for tearing up flesh, but to sink deep into it and hold on to the prey item. The immense bite force, which may be as high as 5,000 lbf (22,000 N) in large adults, ensures that the prey item cannot escape the grip.^[95] Prey taken is often much smaller than the crocodile itself, and such prey can be overpowered and swallowed with ease. When it comes to larger prey, success depends on the crocodile's body power and weight to pull the prey item back into the water, where it is either drowned or killed by sudden thrashes of the head or by tearing it into pieces with the help of other crocodiles.^[19]

Feeding on a dead wildebeest in the Masai Mara

Subadult and smaller adult Nile crocodiles use their bodies and tails to herd groups of fish toward a bank, and eat them with quick sideways jerks of their heads. Some crocodiles of the species may habitually use their tails to sweep terrestrial prey off balance, sometimes forcing the prey specimen into the water, where it can be more easily drowned.^[10] They also cooperate, blocking migrating fish by forming a semicircle across the river.^[36] The most dominant crocodile eats first. Their ability to lie concealed with most of their bodies under water, combined with their speed over short distances, makes them effective opportunistic hunters of larger prey. They grab such prey in their powerful jaws, drag it into the water, and hold it underneath until it drowns. They also scavenge or steal kills from other predators, such as lions and leopards (Panthera pardus).^[11] Groups of Nile crocodiles may travel hundreds of meters from a waterway to feast on a carcass.^[36] They also feed on dead hippopotamuses (Hippopotamus amphibius) as a group (sometimes including three or four dozen crocodiles), tolerating each other. Much of the food from crocodile stomachs may come from scavenging carrion, and the crocodiles could be viewed as performing a similar function at times as do vultures or hyenas on land.^[10] Once their prey is dead, they rip off and swallow chunks of flesh. When groups are sharing a kill, they use each other for leverage, biting down hard and then twisting their bodies to tear off large pieces of meat in a "death roll". They may also get the necessary leverage by lodging their prey under branches or stones, before rolling and ripping.^[10]

The Nile crocodile possesses unique predation behavior characterized by the ability of preying both within water, where it is best adapted, and out of it, which often results in unpredictable attacks on almost any other animal up to twice its size. Most hunting on land is done at night by lying in ambush near forest trails or roadsides, up to 50 m (170 ft) from the water's edge.^[96] Since their speed and agility on land is rather outmatched by most terrestrial animals, they must use obscuring vegetation or terrain to have a chance of succeeding during land-based hunts.^[10][96] In one case, an adult crocodile charged from the water up a bank to kill a bushbuck (Tragelaphus scriptus) and instead of dragging it into the water, was observed to pull the kill further on land into the cover of the bush.^[97] Two subadult crocodiles were once seen carrying the carcass of a nyala (Tragelaphus angasii) across land in unison.^[36] In South Africa, a game warden far from water sources in a savannah-scrub area reported that he saw a crocodile jump up and grab a donkey by the neck and then drag the prey off.^[10][98][99] Small carnivores are readily taken opportunistically, including African clawless otters (Aonyx capensis)^[100]

Interspecific predatory relationships

Living in the rich biosphere of Africa south of the Sahara, the Nile crocodile may come into contact with other large predators. Its place in the ecosystems it inhabits is unique, as it is the only large tetrapod carnivore that spends the majority of its life in water and hunting prey associated with aquatic zones. Large mammalian predators in Africa are often social animals and obligated to feed almost exclusively on land.^[18][99] The Nile crocodile is a strong example of an apex predator. Outside water, crocodiles can meet competition from other dominant savannah predators, notably big cats, which in Africa are represented by lions, cheetahs, and leopards. In general, big cats and crocodiles have a relationship of mutual avoidance. Occasionally, if regular food becomes scarce, both lions and the crocodile will steal kills on land from each other and, depending on size, will be dominant over one another. Both species may be attracted to carrion, and may occasionally fight over both kills or carrion.^[101] Most conflicts over food occur near the water and can literally lead to a tug-of-war over a carcass that can end either way, although seldom is there any serious fighting or bloodshed between the large carnivores.^[11] Intimidation displays may also resolve these conflicts. However, when size differences are prominent, the predators may prey on each other.

Reproduction

A float of Nile crocodiles in Kilimanjaro Safaris at Disney's Animal Kingdom.

On average, sexual maturity is obtained from 12 to 16 years of age.^[53] For males, the onset of sexual maturity occurs when they are about 3.3 m (10 ft 10 in) long and mass of 155 kg (342 lb), being fairly consistent.^[102] On the other hand, that for females is rather more variable, and may be indicative of the health of a regional population based on size at sexual maturity. On average, according to Cott (1961), female sexual maturity occurs when they reach 2.2 to 3 m (7 ft 3 in to 9 ft 10 in) in length.^[11] Similarly, a wide range of studies from southern Africa found that the average length for females at the onset of sexual maturity was 2.33 m (7 ft 8 in).^[103] However, stunted sexual maturity appears to occur in populations at opposite extremes, both where crocodiles are thought to be overpopulated and where they are overly reduced to heavy hunting, sometimes with females laying eggs when they measure as small as 1.5 m (4 ft 11 in) although it is questionable whether such clutches would bear healthy hatchlings.^[60][104]

According to Bourquin (2008), the average breeding female in southern Africa is between 3 and 3.6 m (9 ft 10 in and 11 ft 10 in).^[103] Earlier studies support that breeding is often inconsistent in females less than 3 m (9 ft 10 in) and clutch size is smaller, a female at 2.75 m (9 ft 0 in) reportedly never lays more than 35 eggs, while a female measuring 3.64 m (11 ft 11 in) can expect a clutch of up to 95 eggs.^[11][10] In "stunted" newly mature females from Lake Turkana measuring 1.83 m (6 ft 0 in), the average clutch size was only 15.^[51][60] Graham and Beard (1968) hypothesized that, while females do continue to grow as do males throughout life, that past a certain age and size that females much over 3.2 m (10 ft 6 in) in length in Lake Turkana no longer breed (supported by the physiology of the females examined here); however, subsequent studies in Botswana and South Africa have found evidence of nesting females at least 4.1 m (13 ft 5 in) in length.^{[60][103][105]} In the Olifants River in South Africa, rainfall influenced the size of nesting females as only larger females (greater than 3 m (9 ft 10 in)) nested during the driest years. Breeding females along the Olifants were overall larger than those in Zimbabwe.^[105] Most females nest only every two to three years while mature males may breed every year.^[15][103]

During the mating season, males attract females by bellowing, slapping their snouts in the water, blowing water out of their noses, and making a variety of other noises. Among the larger males of a population, territorial clashes can lead to physical fighting between males especially if they are near the same size. Such clashes can be brutal affairs and can end in mortality but typically end with victor and loser still alive, the latter withdrawing into deep waters.^[106][107] Once a female has been attracted, the pair warble and rub the undersides of their jaws together. Compared to the tender behaviour of the female accepting the male, copulation is rather rough (even described as "rape"-like by Graham & Beard (1968)) in which the male often roars and pins the female underwater.^[60][107] Cott noted little detectable discrepancy in the mating habits of Nile crocodiles and American alligators.^[11] In some regions, males have reportedly mated with several females, perhaps any female that enters his claimed territory, though in most regions annual monogamy appears to be most common in this species.^[23]

Eggs

Females lay their eggs about one to two months after mating. The nesting season can fall in nearly every month of the year. In the northern extremes of the distribution (i.e. Somalia or Egypt), the nesting season is December through February while in the southern limits (i.e. South Africa or Tanzania) is in August through December. In crocodiles between these distributions egg-laying is in intermediate months, often focused between April and July. The dates correspond to about a month or two into the dry season within that given region. The benefits of this are presumably that nest flooding risk is considerably reduced at this time and the stage at which hatchlings begin their lives out of the egg falls roughly at the beginning of the rainy season, when water levels are still relatively low but insect prey is in recovery. Preferred nesting locations are sandy shores, dry stream beds, or riverbanks. The female digs a hole a few metres from the bank and up to 0.5 m (20 in) deep, and lays on average between 25 and 80 eggs. The number of eggs varies and depends partially on the size of the female.^[60] The most significant prerequisites to a nesting site are soil with the depth to permit the female to dig out the nest mound, shading to which mother can retire during the heat of the day and access to water.^[11] She finds a spot soft enough to allow her to dig a sideways slanted burrow. The mother Nile crocodile deposits the eggs in the terminal chamber and packs the sand or earth back over the nest pit. While, like all crocodilians, the Nile crocodile digs out a hole for a nest site, unlike most other modern crocodilians, female Nile crocodiles bury their eggs in sand or soil rather than incubate them in rotting vegetation.^[10][108] The female may urinate sporadically on the soil to keep it moist, which prevents soil from hardening excessively.^[10] After burying the eggs, the female then guards them for the three-month incubation period. Nests have been recorded seldom in concealed positions such as under a bush or in grasses, but normally in open spots on the bank. It is thought the Nile crocodile cannot nest under heavy forest cover as can two of the three other African crocodiles because they do not use rotting leaves (a very effective method of producing heat for the eggs) and thus require sunlight on sand or soil the surface of the egg chamber to provide the appropriate warmth for embryo development. In South Africa, the invasive plant Chromolaena odorata has recently exploded along banks traditionally used by crocodiles as nesting sites and caused nest failures by blocking sunlight over the nest chamber.^[109]

When Nile crocodiles have been entirely free from disturbance in the past, they may nest gregariously with the nest lying so close together that after hatching time the rims of craters are almost contiguous. These communal nesting sites are not known to exist today, perhaps being most recently recorded at Ntoroko peninsula, Uganda where two such sites remaining until 1952. In one area, 17 craters were found in an area of 25 yd × 22 yd (75 ft × 66 ft), in another 24 in an area of 26 yd × 24 yd (78 ft × 72 ft). Communal nesting areas also reported from Lake Victoria (up until the 1930s) and also in the 20th century at Rahad River, Lake Turkana and Malawi.^{[11][110][111][112]} The behaviour of the female Nile crocodile is considered unpredictable and may be driven by the regional extent of prior human disturbance and human persecution rather than natural variability. In some areas, the mother crocodiles will only leave the nest if she needs to cool off (thermoregulation) by taking a quick dip or seeking out a patch of shade.^[10] Females will not leave nest site even if rocks are thrown at her back and several authors note her trance-like state while standing near nest, similar to that of crocodiles in aestivation but not like any other stage in their life-cycle. In such a trance, some mother Nile crocodiles may show no discernable reaction even if pelted with stones.^[11][10] At other times, the female will fiercely attack anything approaching their eggs, sometimes joined by another crocodile which may be the sire of the young.^[10][113] In other areas, the nesting female may disappear upon potential disturbance which may allow the presence of both the female and her buried nest to escape unwanted detection by predators.^[15][60] Despite the attentive care of both parents, the nests are often raided by humans and monitor lizards or other animals while she is temporarily absent.^[114]

At a reported incubation period of about 90 days, the stage is notably shorter than that of the American alligator (110–120 days) but slightly longer than that of the mugger crocodile.^[11][106] Nile crocodiles have temperature-dependent sex determination (TSD), which means the sex of their hatchlings is determined not by genetics as is the case in mammals and birds, but by the average temperature during the middle third of their incubation period. If the temperature inside the nest is below 31.7 °C (89.1 °F), or above 34.5 °C (94.1 °F), the offspring will be female. Males can only be born if the temperature is within that narrow range.^[115] The hatchlings start to make a high-pitched chirping noise before hatching, which is the signal for the mother to rip open the nest.^[116][117] It is thought to be either difficult or impossible for hatchlings to escape the nest burrow without assistance, as the surface may become very heavy and packed above them.^[11][60] The mother crocodile may pick up the eggs in her mouth, and roll them between their tongue and the upper palate to help crack the shell and release her offspring. Once the eggs hatch, the female may lead the hatchlings to water, or even carry them there in her mouth, as female American alligators have been observed doing.^[11][10]

A grouping of yearling baby Nile crocodiles.

Hatchling Nile crocodiles are between 280 and 300 mm (11 and 12 in) long at first and weigh around 70 g (2.5 oz). The hatchlings grow approximately that length each year for the first several years.^[118] The new mother will protect her offspring for up to two years, and if there are multiple nests in the same area, the mothers may form a crèche. During this time, the mothers may pick up their offspring either in their mouths or gular fold (throat pouch) to keep the babies safe. The mother will sometimes carry her young on her back to avoid natural predators of the small crocodiles, which can be surprisingly bold even with the mother around. Nile crocodiles of under two years are much more rarely observed than larger specimens, and more seldom seen than the same age young in several other types of crocodilian. Young crocodiles are shy and evasive due to the formidable array of predators that they must face in sub-Saharan Africa, spending little time sunning and moving about nocturnally whenever possible. Crocodiles two years old and younger may spend a surprising amount of time on land, as evidenced by the range of terrestrial insects found in their stomachs, and their lifestyle may resemble that of a semi-aquatic mid-sized lizard more so than the very aquatic lives of older crocodiles.^[10][103] At the end of the two years, the hatchlings will be about 1.2 m (3 ft 11 in) long, and will naturally depart the nest area, avoiding the territories of older and larger crocodiles.^[10][103] After this stage, crocodiles may loosely associate with similarly sized crocodiles and many enter feeding congregations of crocodiles once they attain 2 m (6 ft 7 in), at which size predators and cannibal crocodiles become much less of a concern.^[10] Crocodile longevity is not well established, but larger species like the Nile crocodile live longer, and may have a potential average life span of 70 to 100 years, though no crocodilian species commonly exceeds a lifespan of 50 to 60 years in captivity.^[9]

Natural mortality of young Nile crocodiles

An estimated 10% of eggs will survive to hatch and a mere 1% of young that hatch will successfully reach adulthood.^[11][60] The full range of causes for mortality of young Nile crocodiles is not well understood, as very young and small Nile crocodiles or well-concealed nests are only sporadically observed. Unseasonable flooding (during nesting which corresponds with the regional dry season) is not uncommon and has probably destroyed several nests, although statistical likelihood of such an event is not known.^[10][60] The only aspect of mortality in this age range that is well studied is predation and this is most likely the primary cause of death while the saurians are still diminutive.^[119] The single most virulent predator of nests is almost certainly the Nile monitor. This predator can destroy about 50% of studied Nile crocodile eggs on its own, often being successful (as are other nest predators) in light of the trance-like state that the mother crocodile enters while brooding or taking advantage of moments where she is distracted or needs to leave the nest. In comparison, perenties (Varanus giganteus) (the Australian ecological equivalent of the Nile monitor) succeeds in depredating about 90% of freshwater crocodile (Crocodylus johnsoni) eggs and about 25% of saltwater crocodile nests.^[119] Mammalian predators can take nearly as heavy of a toll, especially large mongooses such the Egyptian mongoose (Herpestes ichneumon) in the north and the water mongoose in the south of crocodile's range. Opportunistic mammals who attack Nile crocodile nests have included wild pigs, medium-sized wild cats and baboon troops. Like Nile monitors, mammalian predators probably locate crocodile nests by scent as the padded-down mound is easy to miss visually.^[18][119] Marabou storks sometimes follow monitors to pirate crocodile eggs for themselves to consume, although can also dig out nests on their own with their massive, awl-like bills if they can visually discern the nest mound.^[10][119]

Predators of Nile crocodiles eggs have ranged from insects such as the red flour beetle (Tribolium castaneum) to predators as large and formidable as spotted hyenas (Crocuta crocuta).^[119] Unsurprisingly, once exposed to the elements as hatchlings, the young, small Nile crocodiles are even more vulnerable. Most of the predators of eggs also opportunistically eat young crocodiles, including monitors and marabous, plus almost all co-existing raptorial birds, including vultures, eagles, and large owls and buzzards. Many "large waders" are virulent predators of crocodile hatchlings, from dainty little egrets (Egretta garzetta) and compact hamerkops (Scopus umbretta) to towering saddle-billed storks (Ephippiorhynchus senegalensis), goliath herons and shoebills (Balaeniceps rex). Larger corvids and some non-wading water birds (i.e. pelicans) can also take some young Nile crocodiles. Mammalian carnivores take many hatchlings as well as large turtles and snakes, large predatory freshwater fish, such as the African tigerfish, the introduced largemouth bass, and possibly bull sharks, when they enter river systems. When crocodile nests are dug out and the young placed in water by the mother, in areas such as Royal Natal National Park predators can essentially enter a feeding frenzy.^{[119][120][121][122]} It may take a few years before predation is no longer a major cause of mortality for young crocodiles. African fish eagles can take crocodile hatchlings up to a few months of age and honey badgers can prey on yearlings. Once they reach their juvenile stage, large African rock pythons and big cats remain as the only predatory threat to young crocodiles.^[9][10][123] Perhaps no predator is more deadly to young Nile crocodiles than larger crocodiles of their own species, as, like most crocodilians, they are cannibalistic. This species may be particularly dangerous to their own kind considering their aggressive dispositions.^{[10][90][124]} While the mother crocodile will react aggressively toward potential predators and has been recorded chasing and occasionally catching and killing such interlopers into her range, due to the sheer number of animals who feed on baby crocodiles and the large number of hatchlings, she is more often unsuccessful at deflecting such predators.^{[11][10][119]}

Environmental status

Conservation organizations have determined that the main threats to Nile crocodiles, in turn, are loss of habitat, pollution, hunting, and human activities such as accidental entanglement in fishing nets.^[26] Though the Nile crocodile has been hunted since ancient times,^[125] the advent of the readily available firearm made it much easier to kill these potentially dangerous reptiles.^[10] The species began to be hunted on a much larger scale from the 1940s to the 1960s, primarily for high-quality leather, although also for meat with its purported curative properties. The population was severely depleted, and the species faced extinction. National laws, and international trade regulations have resulted in a resurgence in many areas, and the species as a whole is no longer wholly threatened with extinction. The status of Nile crocodiles was variable based on the regional prosperity and extent of conserved wetlands by the 1970s.^[126] However, as is the case for many large animal species whether they are protected or not, persecution and poaching have continued apace and between the 1950s and 1980s, an estimated 3 million Nile crocodiles were slaughtered by humans for the leather trade.^[23] In Lake Sibaya, South Africa, it was determined that in the 21st century, persecution continues as the direct cause for the inability of Nile crocodiles to recover after the leather trade last century.^[127] Recovery for the species appears quite gradual and few areas have recovered to bear crocodile populations, i.e. largely insufficient to produce sustainable populations of young crocodiles, on par with times prior to the peak of leather trading.^[104] Crocodile 'protection programs' are artificial environments where crocodiles exist safely and without the threat of extermination from hunters.^[67]

Large adults in captivity, Djerba, Tunisia

Nile crocodiles in captivity, Israel

An estimated 250,000 to 500,000 individuals occur in the wild today. The IUCN Red List assesses the Nile crocodile as "Least Concern (LR/lc)".^[2] The Convention on International Trade in Endangered Species (CITES) lists the Nile crocodile under Appendix I (threatened with extinction) in most of its range; and under Appendix II (not threatened, but trade must be controlled) in the remainder, which either allows ranching or sets an annual quota of skins taken from the wild. The Nile crocodile is widely distributed, with strong, documented populations in many countries in eastern and southern Africa, including Somalia, Ethiopia, Kenya, Zambia and Zimbabwe.^[2][26] This species is farmed for its meat and leather in some parts of Africa. Successful sustainable-yield programs focused on ranching crocodiles for their skins have been successfully implemented in this area, and even countries with quotas are moving toward ranching. In 1993, 80,000 Nile crocodile skins were produced, the majority from ranches in Zimbabwe and South Africa.^[104][128] Crocodile farming is one of the few burgeoning industries in Zimbabwe.^[129] Unlike American alligator flesh, Nile crocodile meat is generally considered unappetizing although edible as tribes such as the Turkana may opportunistically feed on them. According to Graham and Beard (1968), Nile crocodile meat has an "indescribable" and unpleasant taste, greasy texture and a "repellent" smell.^[60][130]

The conservation situation is more grim in Central and West Africa presumably for both the Nile and West African crocodiles. The crocodile population in this area is much more sparse, and has not been adequately surveyed. While the natural population in these areas may be lower due to a less-than-ideal environment and competition with sympatric slender-snouted and dwarf crocodiles, extirpation may be a serious threat in some of these areas.^[26][131] At some point in the 20th century, the Nile crocodile appeared to have been extirpated as a breeding species from Egypt, but has locally re-established in some areas such as the Aswan Dam.^[23] Additional factors are a loss of wetland habitats, which is addition to direct dredging, damming and irrigation by humans, has retracted in the east, south and north of the crocodile's range, possibly in correlation with global warming.^[23][132] Retraction of wetlands due both to direct habitat destruction by humans and environmental factor possibly related to global warming is perhaps linked to the extinction of Nile crocodiles in the last few centuries in Syria, Israel and Tunisia.^[23][26] In Lake St. Lucia, highly saline water has been pumped into the already brackish waters due to irrigation practices. Some deaths of crocodiles appeared to have been caused by this dangerous salinity, and this one-time stronghold for breeding crocodiles has experienced a major population decline.^[23][133] In yet another historic crocodile stronghold, the Olifants River, which flows through Kruger National Park, numerous crocodile deaths have been reported. These are officially due to unknown causes but analysis has indicated that environmental pollutants caused by humans, particularly the burgeoning coal industry, are the primary cause. Much of the contamination of crocodiles occurs when they consume fish themselves killed by pollutants.^[134][135] Additional ecological surveys and establishing management programs are necessary to resolve these questions.

The Nile crocodile is the top predator in its environment, and is responsible for checking the population of mesopredator species, such as the barbel catfish and lungfish, that could overeat fish populations on which other species, including birds, rely. One of the fish predators seriously affected by the unchecked mesopredator fish populations (due again to crocodile declines) is humans, particularly with respect to tilapia, an important commercial fish that has declined due to excessive predation.^[10] The Nile crocodile also consumes dead animals that would otherwise pollute the waters.

Attacks on humans

Barrier in Uganda to lessen the risk of crocodile attacks

Much of the hunting of and general animosity toward Nile crocodiles stems from their reputation as a man-eater, which is not entirely unjustified.^[136] Despite most attacks going unreported, the Nile crocodile along with the saltwater crocodile is estimated to kill hundreds (possibly thousands) of people each year, which is more than all other crocodilian species combined.^{[9][20][137][138]} While these species are much more aggressive toward people than other living crocodilians (as is statistically supported by estimated numbers of crocodile attacks), Nile crocodiles are not particularly more likely to behave aggressively to humans or regard humans as potential prey than saltwater crocodiles. However, unlike other "man-eating" crocodile species, including the saltwater crocodile, the Nile crocodile lives in close proximity to human populations through most of its range, so contact is more frequent. This combined with the species' large size creates a higher risk of attack.^[9][16] Crocodiles as small as 2.1 m (6 ft 11 in) are capable of overpowering and successfully preying on small apes and hominids, presumably including children and smaller adult humans, but a majority of fatal attacks on humans are by crocodiles reportedly exceeding 3 m (9 ft 10 in) in length.^[16]

In studies preceding the slaughter of crocodiles for the leather trade, when there were believed to be many more Nile crocodiles, a roughly estimated 1,000 human fatalities per annum by Nile crocodiles were posited, with a roughly equal number of aborted attacks.^[10][139] A more contemporary study claimed the number of attacks by Nile crocodiles per year as 275 to 745, of which 63% are fatal, as opposed to an estimated 30 attacks per year by saltwater crocodiles, of which 50% are fatal. With the Nile crocodile and the saltwater crocodile, the mean size of crocodiles involved in non-fatal attacks was about 3 m (9 ft 10 in) as opposed to a reported range of 2.5–5 m (8 ft 2 in – 16 ft 5 in) or larger for crocodiles responsible for fatal attacks. The average estimated size of Nile crocodiles involved in fatal attacks is 3.5 m (11 ft 6 in). Since a majority of fatal attacks are believed to be predatory in nature, the Nile crocodile can be considered the most prolific predator of humans among wild animals.^[140] In comparison, lions, in the years from 1990 to 2006, were responsible for an estimated one-eighth as many fatal attacks on humans in Africa as were Nile crocodiles. Although Nile crocodiles are more than a dozen times more numerous than lions in the wild, probably fewer than a quarter of living Nile crocodiles are old and large enough to pose a danger to humans.^{[140][141][142]} Other wild animals responsible for more annual human mortalities either attack humans in self-defense, as do venomous snakes,^[143] or are deadly only as vectors of disease or infection, such as snails,^[144] rats^[145] and mosquitos.^[146]

Regional reportage from numerous areas with large crocodile populations nearby indicate, per district or large village, that crocodiles often annually claim about a dozen or more lives per year. Miscellaneous examples of areas in the last few decades with a dozen or more fatal crocodile attacks annually include Korogwe District, Tanzania, Niassa Reserve, Mozambique and the area around Lower Zambezi National Park, Zambia.^[147][148] Despite historic claims that the victims of Nile crocodile attacks are usually women and children,^[9] there is no detectable trends in this regard and any human, regardless of age, gender, or size is potentially vulnerable. Incautious human behavior is the primary drive behind crocodile attacks.^[16] Most fatal attacks occur when a person is standing a few feet away from water on a non-steep bank, is wading in shallow waters, is swimming or has limbs dangling over a boat or pier. Many victims are caught while crouching, and people in jobs that might require heavy usage of water, including laundry workers, fisherman, game wardens and regional guides, are more likely to be attacked. Many fisherman and other workers who are not poverty-stricken will go out of their way to avoid waterways known to harbor large crocodile populations.^{[10][60][149]}

Most biologists who have engaged in months or even years of field work with Nile crocodiles, including Cott (1961), Graham and Beard (1968) and Guggisberg (1972), have found that with sufficient precautions, their own lives and the lives of their local guides were rarely, if ever, at risk in areas with many crocodiles.^[11][10][60] However, Guggisberg accumulated several earlier writings that noted the lack of fear of crocodiles among Africans, driven in part perhaps by poverty and superstition, that caused many observed cases of an "appalling" lack of caution within view of large crocodiles, as opposed to the presence of bold lions, which engendered an appropriate panic. Per Guggisberg, this disregard (essentially regarding the crocodile as a lowly creature and thus non-threatening to humans) may account for the higher frequency of deadly attacks by crocodiles than by large mammalian carnivores. Most locals are well aware of how to behave in crocodile-occupied areas, and some of the writings quoted by Guggisberg from the 19th and 20th century may need to be taken with a "grain of salt".^[10][60]

See also

• Pansteatitis

Notes

References

La Nila krokodilo ankaŭ nomata Afrika krokodilo (Crocodylus niloticus) estas afrika krokodilo kiu estas komuna en kelkaj areoj de kelkaj landoj de Orienta Afriko nome en Somalio, Etiopio, Ugando, Kenjo, Egipto, Zambio kaj Zimbabvo sed loĝas ankaŭ en Okcidenta Afriko.

Disvastiĝo kaj vivejo

Antikve la Nila krokodilo loĝis en la Nila delto kaj la Rivero Zarqa, kaj estis konstatitaj de ekzemple Herodoto laŭ kiu ili loĝis en la Lago Moeris. Oni supozas ke ili formortis en la Sejŝeloj komence de la 19a jarcento. Oni scias per fosiliaj restaĵoj ke ili iam loĝis en la Lago Eduardo.^[1] La nuna teritorio de la Nila krokodilo etendas el la Rivero Senegalo, Laĝo Ĉado, Ŭadajo kaj Sudano al la Kunene kaj la Okavanga Delto. En Madagaskaro, krokodiloj loĝas en okcidentaj akj sudaj partoj el Sembirano al Port Dauphin. Ili foje estis vidataj en Zanzibaro kaj en Komoroj.^[1]

En Okcidenta Afriko, Nilaj krokodiloj loĝas plej ofte ĉe marbordaj lagunoj, stuaroj kaj en riveroj borde de la ekvatora arbarzono. En Orienta Afriko ili troviĝas ĉefe en riveroj, lagoj, marĉoj kaj akvorezervujoj. Oni scias ke ili eniras en la maro en kelkaj areoj, kaj eĉ unu specimeno estis vidata 11 km for de la Golfeto de Santa Lucia en 1917. En Madagaskaro ili adaptiĝis al vivo en kavoj. Post tio la krokodiloj povas resti en la neprofundaj partoj de ili aŭ en la ĉirkaŭaĵoj.^[1]

Biologio kaj aspekto

Vidaĵo de Nila krokodilo el flanko

Krokodilo en la Nacia Parko de la Kobe, Bocvano

Crocodylus niloticus - MHNT

Crocodylus niloticus - MHNT

Nilaj krokodiloj havas malhelan bronzecan koloron supre, kun nigraj punktoj dorse kaj malhelpurpuran en ventro. Flankoj, kiuj estas falvecverdaj, havas malhelajn makulojn laŭ oblikvaj strioj. Estas iom da variado relative al sia medio; specimenoj el fluantaj akvoj tendencas esti pli helaj ol tiuj kiuj loĝase en lagoj aŭ marĉoj. Ties okuloj estas verdaj.^[1]

Kiel ĉiuj krokodiloj, ili estas kvarpiedaj kun kvar mallongaj, disetendaj kruroj; longa, povega vosto; skvameca haŭto kun serioj de ostecaj ŝildoj laŭ la tuta dorso kaj vosto; kaj povegaj makzeloj. Ili havas niktitomembranojn por protekti siajn okulojn kaj havas larmotubojn, kaj povas purigi siajn okulojn per larmoj.

Naztruoj, okuloj kaj oreloj estas situaj kapopinte, kaj tiele la resto de la korpo povas resti subakve. Ankaŭ ties koloro helpas ilin kaŝiĝi: junuloj estas grizaj, multkoloraj aŭ brunaj; kun pli malhelaj krucbendoj en siaj vosto kaj korpo. Kiam ili maturiĝas ili iĝas ankaŭ pli malhelaj kaj la krucbendoj svagas, ĉefe tiuj de la korpo. La subventro estas flaveca, kaj el tio eliras bonkvalita ledo.

Ili kutime treniĝas sub siaj ventroj, sed ili povas ankaŭ "alte piediri" havante siajn trunkojn supergrunde. Pli malgrandaj specimenoj povas galopi, kaj eĉ pli grandaj krokodiloj kapablas surprizi per sia rapideco ĝis 12 al 14 km/h. Ili povas naĝi multe pli rapide movante siajn korpojn body kaj vostojn per sinua movmaniero, kaj ili povas plufari tiun movoformon multe pli da 30 al 35 km/h.

Ili havas trikavan koron kiu estas ofte miskomprenita kiel 4-kavan pro longeca kora septum, kiu estas fiziologie simila al la kvarkava koro de birdo, kiuc estas ĉefe efikaj por oksigenigi sian sangon. Ili kutime subnaĝas nur dum paro de minutoj, sed ili povas resti subakve ĝis 30 minutoj se ili estas minacataj, kaj se ili restas senmova ili povas haltigi sian spiron dum 2 horoj. Ili havas ektoterman metabolismon, kaj tiele ili povas survivi longe sen manĝi — kvankam kiam ili povas manĝi, ili povas manĝi ĝis duonon de sia korpopezo dum unu fojo.

Ili havas riĉa voĉon gamon, kaj bonan aŭdkapablon. Ties haŭto havas nombrajn entegmentajn sensorganojn (ISO), kiuj povas reagi al ŝanĝoj en akvopremo.

La forto de la mordo de plenkreska Nila krokodilo estas konsiderata kiel povega ((22 kN)). Tamen la muskoloj responsaj por malfermi la buŝon estas ege malfortaj, permesantaj homon facile reteni fermita la krokodilan buŝon per malgranda forto.^[2] Ties buŝon plenas per totalo de 64 al 68 konusformaj dentoj. Je ĉiu flanko de la buŝo estas 5 dentoj fronte de la supra makzelo (la antaŭmakzelaj), 13 aŭ 14 en la resto de la supra makzelo (la makzelaj), kaj 14 aŭ 15 je ĉiu flanko de la malsupra makzelo (la mandibloj). Junuloj rapide perdas haŭtaĵon el la buŝopinto nomatan la ovodenton, per kiuj ili rompas la ovoŝelon dumnaske.

Referencoj

• Crocodile Specialist Group (1996). Crocodylus niloticus. Internacia Ruĝa Listo de Endanĝeritaj Specioj, eldono de 2006. IUCN 2006. Elŝutita 12 May 2006. Database entry includes a brief justification of why this species is of least concern
• Britton, Adam. (n.d.). Crocodylus niloticus (Laurenti, 1768). Retrieved December 16, 2004 from Crocodilian Species List.
• El-Noshokaty, Amira. (January 17–23, 2002). Lord of the Nile. Al-Ahram Weekly On-line, 569. Retrieved December 16, 2004.
• Nile crocodiles: Temperature dependent sex determination. (February 2000). Pulse of the Planet, 2075. Retrieved December 16, 2004 from Pulse of the Planet.
• Ross, James Perran (ed.). (n.d.). Species Accounts: Crocodylus niloticus. December 16, 2004 from Status Survey and Conservation Action Plan, Second Edition: Crocodiles.

Vidu ankaŭ

• Nord-konga arbara-savana mozaiko
• Viktori-basena arbara-savana mozaiko

El cocodrilo del Nilo (Crocodylus niloticus) es una especie de saurópsido . Es una de las cuatro especies de cocodrilos que habitan en África —junto con el cocodrilo hociquifino africano, el cocodrilo del desierto y el cocodrilo enano—, y una de las más grandes en tamaño en el mundo, solo superado por el cocodrilo marino.^[2]​ pues puede alcanzar los seis m de largo y pesar hasta 700 kg, aunque sus tallas medias son de cuatro metros y de 225 kg.^[3]​

Descripción

Cocodrilo del Nilo devorando un ñu muerto en el Masái Mara (Kenia), mostrando sus dientes.

Puede medir hasta seis metros de largo y pesar hasta 700 kilogramos de peso. Su coloración puede ser verde oliva brillante, verde oscuro o bronce en el dorso y amarillo pálido en el vientre.^[4]​

Su fórmula dental es la siguiente: 18-19/15.^[4]​

Distribución y hábitat

Pese a lo que su nombre común podría dar a entender, no es exclusivo del Nilo, sino que se encuentra en prácticamente toda el África subsahariana y en la isla de Madagascar. Vive en lagos y ríos de agua dulce.

Comportamiento

Su ceremonia de cortejo es espectacular; el macho defiende un trecho de arena, rugiendo a cualquier intruso. Cuando la hembra se siente atraída por el ruido, el macho sacude el cuerpo y expulsa agua por las fosas nasales.

Se alimenta de animales que se acercan a beber; los arrastra al agua y los ahoga. Al comer, como no pueden masticar, utilizan un método que perfeccionaron durante millones de años. Agarran una parte del cuerpo y mientras la tienen sujeta giran todo su cuerpo sucesivamente hasta arrancar un buen trozo de carne; eso se llama "giro de la muerte".

Esta especie de cocodrilo es particularmente agresiva y peligrosa para los seres humanos,^[5]​ siendo solo superada en riesgo por el cocodrilo marino de Australia y el sudeste asiático.

El cocodrilo en la mitología egipcia

Sobek.

Ha sido al mismo tiempo odiado y reverenciado por el hombre, especialmente en el Antiguo Egipto, donde los cocodrilos eran momificados y se les rendía culto. Los antiguos egipcios rendían culto a Sobek, un dios-cocodrilo asociado con la fertilidad, la protección, y el poder del faraón. La relación de los egipcios con Sobek era ambivalente: en ocasiones dieron caza a los cocodrilos, e injuriaron al dios, y otras veces lo vieron como el protector del faraón y origen de su poder.

Sobek era representado como un cocodrilo, o como hombre con cabeza de cocodrilo, con la corona Atef. El principal lugar de culto estaba en una ciudad del Imperio Medio, Shedet, en el oasis de El-Fayum, en árabe al-Fayyum, lugar que era conocido por los griegos con el nombre de "Cocodrilópolis", o la ptolemaica Arsínoe. Otro templo de importancia dedicado a Sobek se encuentra en Kom Ombo.

Según Heródoto, en el siglo V a. C., algunos egipcios tenían cocodrilos como animales domésticos. En el estanque del templo de Sobek, en Arsínoe, vivía un cocodrilo sagrado, al que se alimentaba, cubría de joyas y rendía culto. Cuando los cocodrilos morían eran embalsamados, momificados, depositados en sarcófagos y enterrados en tumba sagrada. Han sido hallados cocodrilos momificados en sepulturas egipcias, incluso huevos de cocodrilo embalsamados.

En el antiguo Egipto se utilizaba la magia para aplacar a los cocodrilos. Incluso en la época actual, los pescadores nubios ponen cocodrilos disecados en los umbrales de sus puertas para prevenir el mal.

El cocodrilo se relacionó también en ocasiones con Seth, el dios del mal.

Referencias

Galería

• Adulto en el
  Parque Nacional Kruger, Sudáfrica.

• Lago Baringo, Kenia.

• Adulto en Zambia.

• Lago Chamo, Etiopía.

• Parque nacional de Chobe, Botsuana.

• Parque nacional Kruger, Sudáfrica.

• skull - MHNT

• Crocodylus niloticus - MHNT

Crocodylus niloticus

Crocodylus niloticus

Niiluse krokodill (Crocodylus niloticus) on krokodilliliik.^[1]

Klassifikatsioon

Niiluse krokodillidel klassifitseeritakse roomajate andmebaasis järgmised alamliigid^[2]:

• Crocodylus niloticus africanus Laurenti, 1768
• Crocodylus niloticus chamses Bory de Saint-Vincent, 1824
• Crocodylus niloticus cowiei (Smith in Hewitt, 1937)
• Crocodylus niloticus madagascariensis Grandidier, 1872
• Crocodylus niloticus niloticus Laurenti, 1768
• Crocodylus niloticus pauciscutatus Deraniyagala, 1948
• Crocodylus niloticus suchus GEOFFROY, 1807.

Levila

Neid Aafrika suurimaid (isased kuni 5 m pikkused) krokodille võib kohata Aafrikas, sh Sambias^[3], ja Madagaskaril.

Kokkupuuted inimestega

Niiluse krokodillid võivad elada 75–100 aasta vanuseks, seega kokkupuuteid inimestega tuleb ikka ette. Ründavad kokkupuuted võib jagada kaheks:

1. inimesed võivad osadele neist saakloomadeks olla (keskmiselt kuni 200 krokodillirünnet aastas)^[4];
2. nemad on inimestele jahiloomadeks (krokodillikütid, jahitrofeedeks^[5] ja ka naha pärast. 1980ndatel võis kütitud niiluse krokodillide arv olla 1000–2000 isendi vahel.^[3]

Viited

Välislingid

• Sissekanne CITES-is
• Sissekanne IUCN-is
• Sissekanne NCBI-s
• Sissekanne Roomajate andmebaasis
• Sissekanne SITI-s
• Sissekanne saidil Wikispecies
• Heiki Suurkask, Mis on vahet krokodillil ja alligaatoril, kaimanil ja gaavialil, veebiversioon (vaadatud 11.03.2014)

Selles artiklis on kasutatud prantsuskeelset artiklit fr:Crocodile du Nil seisuga 11.03.2014.

Crocodylus niloticus

Crocodylus niloticus

Nilotar krokodilo (Crocodylus niloticus) Crocodylus generoko animalia da. Narrastien barruko Crocodylidae familian sailkatuta dago.

Ezaugarriak

Oro har 5 m inguru izaten da luze eta 225 kg pisatzen du batezbestez, baina krokodiloak hil arte hazten dira eta 6 metro eta 700 kiloko (eta gehiagoko) arrak behin baino gehiagotan ikusi eta aztertu dira. Bere pisua 150-700 kilo artean doa eta inoiz ikusitako nilotar krokodilo handiena 900 kilo inguru pisatzen omen zuela estimatzen zen. Krokodilo azpiespezie hau, beraz, Afrikako espezie guztietan handiena eta mundu mailako bigarren handiena (itsas krokodiloaren atzetik soilik) da. Hiruki egiturako mutur luzea du. Lepotik atzerako gaineko aldean karatxo moduko koskorrak ditu, lerrotan ondo definituak. Orban beltzez beteriko brontze-berdexka kolorekoa du bizkarra, sabela, aldiz, horixka.

Munduko bigarren hozkadarik indartsuena du, soilik itsas krokodilo lehengusuaren atzetik.

Bere hortz-formula: 18-19/15.

Hedapena eta habitat

Afrikako tropikoko eta inguruetako ibaietan, Madagaskarren, Komore eta Seychelle uharteetan bizi da.

Portaera

Errunaldia

Hondarretan zuloa eginda erruten ditu arrautzak.^[2]

Elikadura

Nilotar krokodiloa ehizatu dezakeen guztia jaten du, sarraskiak ere gustora jaten ditu.

300 kiloko krokodilo gazteek antilopeak, narrastiak, arrainak, hegaztiak, ñuak eta zebra gazteak ehizatzen dituzte.

400 kilotik gorako krokodiloek ñuak, zebra helduak, jirafa gazteak eta afrikar bufalo gazteak ehizatzen dituzte.

500-700 kiloko krokodilo heldu garatuak eta erraldoiak edozer gauza ehizatzeko gai dira, aurretik aipatutako harrapakin zerrendari jirafa eta afrikar bufalo heldu eta handienak erantsi beharko genioke. 500 kilotik gorako krokodiloek, elefante, errinozero eta hipopotamo helduak izan ezik, edozein animalia atzeman eta urperatu dezakete itotzeko.

Batzuetan, beste harrapari batzuk erortzen dira bere baraileetan; despistaturiko lehoinabarrak, afrikar txakur basatiak, txakalak, hienak eta lehoiak (soilik krokodilo handienak eta uretan bada).

Ehizatze teknika

Niloko krokodiloek, krokodilo guztiek bezala, harrapakin txikiak hozkadez hil eta irensten dituzten bitartean, harrapakin handiei heltzen diete (lepotik, hankatik edo ahal duten edozein lekutik) eta krokodiloa beraren pisua erabiliz harrapakin horiek ibaian urperatuz itotzen dituzte.

Ñuak, zebrak, bufaloak eta tamainu horretako harrapakinei ibaira ur edatera hurbiltzen uzten diete, urpean hurbiletik zelatatzen dituzten bitartean, eta bat batean eraso azkarra egiten dute harrapakinari heltzen saiatzeko. Erasoak helburua lortu badu, orduan harrapakina poliki-poliki ibaira barneratzen saiatuko da (bere pisua erabiliz), itotzeko sakonera nahikoa lortzeko asmoz.

Behin harrapakina hilda dagoenean, bere gorputza ziztu bizian biratuz ("heriotzaren bira" izenaz ezagutzen dena) haragi puskak lortzen ditu, ondoren, osoak irensteko.

Mehatxu naturalak

Lehorrean dagoenean, abantaila galduta (lurrean animalia motela da), lehoiak benetako arrisku edo mehatxu izan daitezke. Lehorrean lehoiengandik hilik eta ehizatuak suertatu diren krokodiloak ezagutzen dira. Dena den, krokodilo helduak ez dute harraparirik, janariagatik baino gehiago lehoiek lehiakide edo kumeentzat arriskua direlakoan hil ditzakete krokodilo helduak, eta beti ere lehorrean.

Krokodilo gazteak lehoinabarren atzaparretan ere eror daitezke ( lehorrean lehoinabarrak krokodilo gazteak ehizatzen ikusi dira).

Krokodiloak hipopotamoen ur eremuetara sartuko balira, arrisku larrian egongo lirateke. Hipopotamoek biziki defendatzen dute beraien ur-eremua, eta horretarako bertan gonbidapenik gabe sarzen diren animalia ezezagun guztiak erasotzen dituzte (hil arte askotan). Hipopotamoak mehatxu handia dira krokodiloentzat, baita ale erraldoientzat ere (hipopotamoa krokodilo alerik handiena baino 4 aldiz handiagoa da). Hozkada batekin hipopotamo batek krokodilo heldu bat hil lezake, eta hipopotamoen erasoak filmatu dira.

Erreferentziak

• TIGR Reptile Database in Species 2000 and ITIS Catalogue of Life: 2011 Annual Checklist

Ikus, gainera

• Crocodylus
• Crocodylidae