Crotalus durissus unicolor Van Lidth de Jeude 1887

Crotalus unicolor is one of the rarest of the rattlesnakes; it was once found on much of Aruba Island and possibly other West Indies Islands. However, this species is now mainly confined to the southern end of Aruba, due largely to habitat destruction tied to tourism industry development.

Biogeographic Regions: neotropical (Native )

Other Geographic Terms: island endemic

There are no reported natural predators of Aruba Island rattlesnakes, which are top predators in these habitats. Human encroachment and poaching for rattles and the pet trade are currently the primary threats to the population.

'Crested caracaras Caracara cheriway', 'merlins Falco columbarius', and 'osprey Pandion haliaetus' are possible snake eating species that are found on Aruba, but no specific information about possible predation threats to young rattlesnakes was found. Their cryptic coloration, venom, and habit of warning potential predators of their threat is likely to protect them from much predation.

Known Predators:

• humans (Homo sapiens)

Anti-predator Adaptations: cryptic

As with most other rattlesnakes, Aruba Island rattlesnakes are heavy bodied, with a triangular head and a rattle-tipped tail. Dorsal scales are triangular and overlapping, with a slight keel. Diamond-shaped markings are present in a variety of colors ranging from a scarcely discernable white or rust color to an obvious dark brown or blue-gray. These markings blend into a pair of dark lines on either side of the spine which terminate at the head. The body color is also variable from light pink to dark tan, occasionally leaving the markings indistinguishable save for a small band along the spine. There are few markings on the head of this species; at most paired stripes extend from the eye toward the ventral boarder of the jaw. Conspicuous heat-sensing pits are visible below and slightly posterior to the nostrils, one on each side.

Range mass: 14 (low) g.

Average length: 1 m.

Other Physical Features: heterothermic ; venomous

Sexual Dimorphism: male larger

Expected lifespan in captivity and in the wild is between 12 and 20 years.

Typical lifespan
Status: wild: 12 to 20 years.

Typical lifespan
Status: captivity: 12 to 20 years.

Aruba Island rattlesnakes inhabit undisturbed sandy, rocky and arid hillsides of this volcanic island, now totaling only 12 square miles of protected land that includes the Arikok National Park. They are typically found on terraced mountainsides consisting of igneous rock and dry stream beds. The diabase mountains and limestone plateaus have been found to harbor the largest densities of this species, possibly due to the relatively low human presence. They are found from 2 meters above sea level to 188 meters elevation on Mount Jamanota. Oddly, despite the seeming preference for undisturbed areas, Aruba Island rattlesnakes are found within 1 km of the two largest cities on the island.

There is little seasonal variation in temperature in this tropical marine habitat; the average temperature is approximately 81 F (27 C) with daily average highs of 84 F and lows of 78 F. Summers tend to be slightly warmer in temperature – up to average highs of 89 F.

Range elevation: 2 to 188 m.

Habitat Regions: tropical ; terrestrial

Terrestrial Biomes: desert or dune ; scrub forest ; mountains

These reptiles hunt with the aid of their heat sensing pits, sight, and smell. Targeted species are mainly rodents, birds, and lizards, especially teiids. After prey is located, these snakes position themselves in a striking stance, characterized by an ‘S’ shaped neck. Launching itself forward, these rattlesnakes opens its mouth, allowing two venom delivering fangs to fold down and sink into the prey animal. The venom contains numerous chemicals, most notably proteolytic enzymes which begin to digest the animal before ingestion while other chemicals are responsible for increasing venom uptake and blocking energy to vital systems. After striking, the animal exhibits a period of increased tongue flicking in order to find the envenomatted prey. Interestingly, this behavior is still present when offering live rodents to captive adult animals raised on frozen or thawed (dead) rodents.

Upon debilitation of the prey, these snakes consume their prey whole by unhinging the lower jaw and stretching the mandibular symphysis at the front of the lower jaw. Only feeding perhaps once to a few times per year, the digestive system of these rattlesnakes is reactivated upon ingestion of the food, increasing blood flow to the digestive organs that are dormant during fasting periods, and probably causing a spike in metabolic rate, as observed in other rattlesnakes.

Animal Foods: birds; mammals; reptiles

Primary Diet: carnivore (Eats terrestrial vertebrates)

Aruba Island rattlesnakes are top trophic level predators to many small lizards, mammals, and birds. They lack natural predators as adults, their main threat being humans.

Commensal/Parasitic Species:

• Reptilian Calicivirus Crotalus type 1
• Ophidian Paramyxovirus Pneumonia

Though illegal, a source of some of the threat to these animals is thought to be capture for the pet trade. More recently, increased education has elevated these animals to national symbols, generating tourism to Arikok National Park. The presence of these snakes was instrumental in spurring the development of this park. Increased research efforts have also occurred in recent years, bringing more money to the island.

Positive Impacts: pet trade ; ecotourism ; research and education; controls pest population

Aruba Island rattlesnakes only attack when provoked, but envenomation can be debilitating or life-threatening to a human who is bitten.

Negative Impacts: injures humans (bites or stings, venomous )

Fertilization in Aruba Island rattlesnakes is internal and occurs during the September through January breeding season. Mated females give birth to 5 to 15 live young after four months of gestation. The autonomous young have already developed fully functional venom sacs at this time and average 20 cm in length and 14 g in weight. After their first shedding, the young begin to hunt for their first meal. They may double or triple in size in the first year. At four years for males and five years for females, they reach reproductive maturity and begin to breed.

Ecological destruction in the form of charcoal and firewood industry, aloe cultivation, and resort and tourism development has reduced the undisturbed habitat available for Aruba Island rattlesnakes to only twelve square miles. Even in these twelve square miles, there is a growing feral goat population that has been destroying native vegetation. This problem has begun to be addressed with growing support for the preservation of the island's endemic species. Media campaigns and education programs highlight the ecological and economic importance of this native rattlesnake. An improved public image has emerged from articles, interviews, and educational efforts, resulting in the Aruba Island rattlesnake being featured on new currency and postage stamps. Conservation posters are being developed by the Association of Zoos and Aquariums (AZA) to further promote these efforts.

Along with this growing respect for the snakes, the AZA Aruba Island Rattlesnake Species Survival Plan (SSP) helped establish the Arikok National Park. The park consists of 19% of Aruba’s land and includes most of the rattlesnake population. There are also plans underway to remove feral goats and list the species in CITES, Appendix II to ban trade of the snakes into the pet trade and sales of the rattles.

There are currently approximately 230 of these rattlesnakes left in the wild and about 110 managed by the AZA (53 females and 57 males) in zoos. The government donated ten wild caught individuals to help with the breeding program in the SSP and help investigate the details of the breeding physiology and release capabilities. Also, animals not used in breeding are being used to test a vaccine for Paramyxovirus, which has killed several SSP snakes.

Another major issue that is currently being researched is the effects of the introduction of large boas, Boa constrictor, to Aruba.

US Federal List: threatened

CITES: no special status

IUCN Red List of Threatened Species: critically endangered

As in all members of the "pitviper" group, subfamily Crotalinae, these rattlesnakes possess a pair of pit organs located below the nostrils. These organs contain infrared receptors that provide information on the body heat, and thus distance, size, and shape, of potential predators and prey. These allow the snakes to hunt during low light conditions, such as during warmer months when they are nocturnal. The directionality of this sense is a result of the physical structure of the pit. Heat information enters the pit much as light enters an eye, and is detected on a curved membrane similar to the way the retina detects the origin of light. It is important to note that this method of detection is more effective in detecting endothermic (mammalian or avian) prey than other ectothermic species and sight is still used in conjunction with infrared sensory detection.

Another form of communication with other species is the series of hollow, keratinized structures that form the rattle at the tip of the tail. The tip of the tail is moved through muscle movement and the vibrations produce a characteristic sound used to warn potential predators.

Pheromones are an important chemical attractant and cue. These rattlesnakes can pick up odors using both the sense of smell and the vomero-nasal (Jacobson’s) organ, where chemicals are supplied by the tongue. The sense of smell is extensive in Aruba Island rattlesnakes, as in most snakes.

Communication Channels: visual ; tactile ; acoustic ; chemical

Other Communication Modes: pheromones ; vibrations

Perception Channels: visual ; infrared/heat ; tactile ; vibrations ; chemical

Aruba Island rattlesnake venom is thought to be among the most toxic of any rattlesnake. Crotalus unicolor was thought to be extinct before efforts were made to investigate "former" habitats.

When a female is reproductively receptive, she will emit a pheromone attractant to signal males of this state. Attracted males will compete for the attention of females by “wrestling”. In this form of combat, the two snakes will rear up and entwine the front half of their length in attempts to push the opponent down. Venom is never used in these battles. Once a male has gained access to a female, courtship continues in a fashion common to many snake species. The male comes in contact with the female, lines up along side of her, and runs his lower jaw along the female’s spine. The tongue of the male is continually flicking and the lateral body movement is in a jerky manner, presumably to differentiate courtship from incidental contact. If receptive, the female permits access to her cloaca by lifting her tail. The male then wraps his tail around hers and inserts one prong (of one of the paired hemipenes)into her cloaca. The pair may continue to mate for several hours at a time.

Mating System: polygynandrous (promiscuous)

This is an ovoviviparous species; the eggs of the female are retained within the body, and maternal nutrient sharing with the embryos has not been demonstrated. At the end of the four month gestation period, the young emerge from the female as live young, leaving the egg membranes inside the female. Typically 5 to 15 young will emerge during the spring as fully independent snakes. The generation interval has been defined as ten years in all management predictions. Ongoing research will attempt to determine if sperm storing occurs in females.

Breeding interval: Breeding occurs once yearly.

Breeding season: Breeding occurs from September through January, with births occuring from January through April (birth).

Range number of offspring: 5 to 15.

Average gestation period: 4 months.

Average time to independence: 0 minutes.

Average age at sexual or reproductive maturity (female): 5 years.

Average age at sexual or reproductive maturity (male): 4 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; sexual ; ovoviviparous

The only parental investment in this species is pre-fertilization and gestational, as the young are independent upon birth. The female is burdened with the majority of this investment, as producing and yolking eggs is energetically expensive. Carrying the developing young for four months is a physical as well as a nutritional burden on her body; the young increase her body size, probably making hunting and feeding difficult.

Male investment consists of sperm production and the energy necessary for courtship and female defense; it is considered negligible compared to that of the female.

Parental Investment: no parental involvement; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)

This snake is nocturnal in the warmer months, though during the rest of the year it is active in the early morning and late afternoon. It feeds on small rodents, birds, and lizards, locating them with a pair of heat sensitive pits that are found between the eyes and nostrils (5). Like other rattlesnakes it injects its prey with a lethal cocktail of chemicals which kills the prey and begins to digest it from the inside (2). The snake then swallows the prey (5). In the wild, the Aruba Island rattlesnake may only eat a few times a year (2). The mating season lasts from September to January, and unlike most snakes, the Aruba Island rattlesnake is viviparous with females giving birth to live young rather than producing eggs (4). Females have small litters of five to nine young. The young are born weighing about 14 grams and are only a few inches long. They have fully functioning venom sacs or glands, and are independent from birth (2). Individuals live for between 15 and 20 years (4).

The Government and people of Aruba do recognise this endemic species as important, and have set aside a large area of interior land as protected habitat for this and other species (2). The American Zoo and Aquarium Association (AZA) Aruba Island rattlesnake Species Survival Plan (SSP) is currently building on the island's conservation efforts. Field research is being carried out to determine population size, natural history traits and factors affecting the survival of the Aruba Island rattlesnake in order to best inform conservation efforts. There is also an ongoing public relations campaign to change local people's perceptions of this venomous snake (6). Captive breeding has also been initiated in zoos associated with the SSP program, to increase population numbers and the genetic health of this threatened snake (4) (6).

The Aruba Island rattlesnake is one of the rarest rattlesnakes in the world (2). Its short and stocky looking body has an overall brown colour and a lighter brown tail tip and its scaly skin has distinctive pink, blue and brown diamond shaped markings (4). Males and females are similar in appearance though males are larger in size. The tail creates the rattling noise that gives this snake its name. This species belongs to the family of vipers, and like other vipers it has a V shaped head, and venomous long hollow fangs which fold against the roof of the mouth when they are not being used (5).

Aruba Island is volcanic and the environment is rocky, dry and covered with cactus scrub and thorny plants (4).

As its name suggests, this species is found on Aruba Island, located off the coast of Venezuela. The island has an area of only 12 square kilometres (2).

Classified as Critically Endangered (CR) on the IUCN Red List 2007 (1), and listed on Appendix III of CITES (3).

This species is threatened because it only occurs on one small island, where just ten square kilometres of habitat remains undisturbed. In past centuries much of the island's trees were cut down for charcoal and firewood, removing this snake's shelter and prey (6). Recent threats include resort development on the island and other forms of human encroachment. Goats have been introduced and have wreaked havoc on the vegetation. This species is also caught and illegally exported for the pet trade (4).

Common names: Aruba rattlesnake, Aruba island rattlesnake, Cascabel (Papiamento).

Crotalus unicolor, or the Aruba Island Rattlesnake, is a venomous pit viper species endemic to the Caribbean island of Aruba, off the coast of Venezuela. It is sometimes still classified as a subspecies of Crotalus durissus.

Crotalus durissus unicolor es una subespecie de C. durissus, una serpiente de la familia de las víboras (Viperidae) que solo se encuentra en la isla caribeña de Aruba, frente a las costas de Venezuela. Está en peligro crítico de extinción, se estima que menos de 230 adultos sobreviven en la naturaleza.

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Crotalus unicolor Crotalus generoko animalia da. Narrastien barruko Viperidae familian sailkatuta dago.

Crotalus unicolor este o specie de șerpi din genul Crotalus, familia Viperidae, descrisă de Lidth De Jeude 1887. A fost clasificată de IUCN ca specie pe cale de dispariție (stare critică). Conform Catalogue of Life specia Crotalus unicolor nu are subspecii cunoscute.

Crotalus durissus unicolor là một phân loài rắn độc được tìm thấy chỉ trên hòn đảo Aruba thuộc vùng Caribbean, ngoài khơi bờ biển Venezuela. Loài này đứng trước nguy cơ tuyệt chủng, ước tính chỉ có không đến 230 cá thể trưởng thành còn sống trong tự nhiên. Đôi khi vẫn được phân loại như là một loài riêng biệt.