Although there are no definitive measures of the lifespan of Hamilton's frogs, estimates have been made that they may live to be 23 years old.
Typical lifespan
Status: wild: 23 (high) years.
Known predators of Hamilton's frogs are native New Zealand tuataras as well as black rats that have been introduced to the area.
Hamilton's frogs exhibit cryptic coloration; its brown and slightly green appearance allows it to camouflage itself among the surrounding rocks, logs and vegetation. When disturbed by predators, it stiffens its body in an attempt to go unnoticed and may remain this way for extended periods of time. These frogs may also take a stiffened, upright stance with legs extended to deter predators. Hamilton’s frogs also secrete a distasteful substance from its granular glands to prevent being eaten by the predator.
Known Predators:
Anti-predator Adaptations: cryptic
Hamilton's frogs are mostly brown in color, with a dark brown or black stripe on each side of the head, running the length of the head and passing through the eye. Unlike most frogs which have slit-like pupils, Hamilton's frogs have round pupils. Present on its back, sides, and appendages are visible rows of granular glands that a secrete distasteful fluid when the frog is disturbed by predators. Female frogs are usually larger than males; females have a snout-vent length ranging from 42 to 47 mm while male lengths range from 37 to 43 mm. Like other native New Zealand frogs of the family Leiopelmatidae, L. hamiltoni has ribs that are not fused to vertebrae.
Once hatched, young froglets appear to be miniature adults with tails. During development, these tails gradually disappear and the frog takes its permanent adult form.
Range length: 37 to 47 mm.
Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry ; poisonous
Sexual Dimorphism: sexes alike; female larger
Although it has no vocal chords and cannot call like other frogs, Leiopelma hamiltoni does emit squeaks or chirps in response to predators or during mating. The function of the squeaks during mating is not completely understood, but it is speculated that they might be emitted upon the male release of sperm during mating.
Due to the fact that Hamilton's frogs lack an external eardrum, noise perception is limited to noises with low frequencies.
Hamilton's frog uses the specific odors emitted by its feces to communicate with its relatives and other frogs. Chemically, the feces of each frog are somewhat different. Frogs can distinguish relatives from intruders by simply smelling a pile of feces. By defecating in a certain area, frogs are able to claim foraging territories as well as prevent intruders from coming near. If a frog encounters a pile of feces, it can determine the size of the individual who left it and decide whether to stay or flee.
Hamilton's frog is a nocturnal species and thus has eyes that are well adapted for seeing in low intensity light. Features of its eye which allow such sight include a high ratio of receptor cells to ganglia, as well as large rod segments and relatively few cone photoreceptor cells.
Communication Channels: visual ; tactile ; chemical
Other Communication Modes: scent marks
Perception Channels: visual ; acoustic ; chemical
Hamilton's frogs historically inhabited coastal forests, but are now limited to a 600 square meter, rocky area known as the “frog bank” at the peak of Stephens Island. This area was initially covered with dense vegetation, but was later deforested when grazing farm animals moved into the area. Fortunately, some of the cover was restored after 1951 when a fence was built to keep other animals out of the area. Today, the vegetation consists mainly of grasses and small vines. The many deep crevices within the rock provide a cool, moist, suitable environment for the frog to inhabit during the day. Hamilton’s frogs live in temperatures ranging from approximately 8 °C in the winter to 18°C in the summer. They inhabit elevations around 300 m above sea level.
Average elevation: 300 m.
Habitat Regions: temperate ; terrestrial
Terrestrial Biomes: forest
Aquatic Biomes: coastal
Leiopelma hamiltoni has a very narrow geographic range, residing only on Stephens Island, New Zealand. Stephens Island lies in the Marlborough Sounds, off of the coast of the South Island of New Zealand. The area of the island is approximately one square mile, but the population resides in a 600 square meter area on the southern tip. Skeletal remains of Hamilton's frog have been found in Waitoma, Hawkes Bay, and Wairarapa on the North Island of New Zealand, indicating that its previous geographic range was much wider.
Biogeographic Regions: oceanic islands (Native )
Other Geographic Terms: island endemic
Hamilton’s frogs are insectivores, feeding on a wide variety of invertebrates including fruit flies, small crickets, moths, and springtails. Juveniles with a snout-vent length of 20 mm or less lack teeth, and thus are required to eat soft-bodied arthropods like mites and fruit flies.
The feeding behavior of Hamilton's frogs is different from that of most other frogs. Most frogs use their protrusible tongues to snag prey, but because the tongues of Hamilton's frogs is attached to the floor of their mouths, frogs must move their entire heads to capture prey.
Animal Foods: insects; terrestrial non-insect arthropods
Primary Diet: carnivore (Insectivore )
Hamilton's frogs serve as prey for native New Zealand tuataras and introduced black rats that live on the island. Conversely, Hamilton's frogs prey upon multiple species of soft-bodied insects. Hamilton's frogs are also vulnerable to the deadly chytrid fungus which has caused huge declines, or extinctions, in amphibian populations across the globe.
Commensal/Parasitic Species:
There are no known positive effects of Leiopelma hamiltoni on humans.
There are no known negative effects of Leiopelma hamiltoni on humans.
Hamilton's frogs undergo almost all development while in the egg. Development is direct, so tadpoles are not formed. Instead, hatchlings which resemble miniature adults emerge from the eggs. Most froglet features are the same as an adults, except for the temporary tail which eventually is lost.
Development - Life Cycle: metamorphosis
Hamilton's frogs are an endangered species according to the ICUN Red List. Recent estimates speculate that there are fewer than 300 individuals left, all of which reside on Stephens Island. Threats to Hamilton’s frogs include predation by native tuataras, as well as introduced mammalian predators like black rats. Although no cases have been reported in L. hamiltoni yet, the species may be susceptible to a deadly fungal disease called chytridiomycosis or chytrid fungus. The disease has been has been acquired by its relative Leiopelma archeyi.
The New Zealand Department of Conservation monitors the population size, and currently has a program in place in attempt to restore it to its former numbers. Efforts to protect the population include building a fence around the "frog bank" to keep predators out, as well as transporting a portion of the population to a nearby island to try and expand its range.
CITES: no special status
IUCN Red List of Threatened Species: endangered
Unlike other frogs, Hamilton's frogs do not use calls as a primary method of finding a mate. They lack eardrums as well as vocal chords, so have no way of producing or perceiving calls. Although no calling is done, Hamilton's frog has been known to emit tiny chirps or squeaks during the breeding season.
Like most frogs, the mating posture for Hamilton's frogs is amplexus; a position in which the male grasps the female from behind with his forelegs. Fertilization is external, occurring during amplexus when the male and female are in close contact.
The mating system is not known.
Hamilton's frog breeds once per mating season, sometime between October and December of each year. Eggs are laid in cool, moist places, often under stones or logs that are present on the forest floor. They are laid in multiple strings that tend to clump together. The number of eggs laid usually ranges from seven to nineteen. Each egg has a visible yolk that is surrounded by a clear capsule comprised of three layers: an inner vitelline membrane, a middle gel-like layer, and a protective outer coat.
Once the eggs are laid, it takes approximately 7 to 9 weeks for them to hatch. After hatching, the juveniles spend an additional 11 to 13 weeks completing their development, undergoing such changes as the loss of the tail and further development of the limbs. It takes approximately 3 to 4 years for juveniles to reach sexual maturity.
Breeding interval: Hamilton's frogs breed once annually.
Breeding season: Hamilton's frogs breed from October to December.
Range number of offspring: 7 to 19.
Range time to hatching: 7 to 10 weeks.
Average time to hatching: 9 weeks.
Average age at sexual or reproductive maturity (female): 3 to 4 years.
Average age at sexual or reproductive maturity (male): 3 to 4 years.
Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization (External ); oviparous
Before fertilization occurs, male frogs seek out and occupy a spot for the female to lay her eggs. Males have been observed to remain at these spots for long periods of time (weeks to months) before the eggs are actually laid. After the eggs are laid, the males stay at the nest and brood. They protect them and maintain a relatively stable environment for them to develop in.
After hatching, the young climb onto the hind legs and backs of the males. Juveniles complete their development here, leaving when the tail has been completely lost and they have reached a snout-vent length of 12 to 13 mm. This male parental care likely serves to keep the young moist, reduce predation, and perhaps reduce fungal infection.
Parental Investment: male parental care ; pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Protecting: Male); pre-weaning/fledging (Protecting: Male)
The Hamilton's frog (Leiopelma hamiltoni) is a primitive frog native to New Zealand, one of only four extant species belonging to the family Leiopelmatidae. New Zealand's frog species all are in the family Leiopelmatidae.[3] The male remains with the eggs to protect them and allows the tadpoles to climb onto his back where they are kept moist.[4] It is named in honour of Harold Hamilton the collector of the type specimen.[5][6] The holotype is in the collection of the Museum of New Zealand Te Papa Tongarewa.[6]
They are mostly light brown in colour, although some green individuals have also been observed. A single dark stripe runs along each side of the head and through the eye.[7] There is no webbing between the hind toes, and the fingers are not webbed.[8] These frogs have a snout length of 5.5 mm, and thighs that can reach up to 14.8 mm.[9]
Leiopelma hamiltoni is a very small frog species, with males being even smaller than females. Males have a snout-vent length of up to 43 millimeters and up to 49 millimeters for females. They are typically a brown color which can range from very light brown to almost black. Some have also been spotted having a green color. They also have black spots covering their bodies. Unlike other frogs, they have very little to no webbing on their hind toes and also do not have external eardrums.[10] They have a row-like design down the back and sides of their body which are made up of callus-like glands in their skin. This coloration allows the frogs to blend in well with their surroundings. These rows start right at the back side of the eye, with the middle row being the largest and most distinct. The end of this middle row terminates at what scientists called the paratoid gland. The lines are also seen on the legs, feet, and arms but are less prominent than the ones on its back.[11]
Hamilton's frog live only on a small rocky area on mammal-free Stephens Island in the Cook Strait. Sub-fossils indicate Hamilton's frog once lived throughout the lower North Island and upper South Island.[12] They live around rocky, moist and grassy areas.[7]
Leiopelma hamiltoni are typically found on the Stephens and Maud Islands, located in the Marlborough Sounds region of New Zealand. Maud island is very small with steep hills, only spanning about 760 acres. The estimated population size of Leiopelma hamiltoni on Maud Island is around 19,000, with the minimum population estimate being around 6,500. The population is much smaller on Stephans Island, with a population estimate of about 200 to 300 individuals. They reside in a small patch at the peak of Stephan's Island which is known as “frog bank”.[13] However, fossils show that the species may have previously had a larger range, with fossils being found scattered all over New Zealand. Remains have been found at Waitoma, Hawkes Bay, and Wairarapa, which are all located on the North Island of New Zealand.[14] Much of the island has been modified due to farming, forcing all the frogs to live in the same section of rainforest that remains.[13]
These frogs are nocturnal, so they are the most active at night. They will occasionally come out during the day to feed, as long as there are humid and moist conditions. They prefer cool and misty nights and are most active when temperatures are between 8 degrees celsius to 14 degrees celsius. They do not travel far, and will usually stay within a 5 meter radius for multiple years at a time. Individuals will also hide and rest in the same spot, typically in a damp rock or log crevice. The frogs will co-habit these retreat sites, with multiple frogs residing inside at a time.[15] This species typically live very closely to one another which would signal socialith. However, since their habitats have become so small, it is unclear whether they do this for social reasons or simply because there is not much space to spread out.[16] Leiopelma hamiltoni also live for an extremely long time, compared to other frog species. Tagged frogs had been found to have lived up to 30 years after their initial tagging. Scientists have estimated that their likely life span is around 23–33 years. They also have unique hunting habits, as they catch their prey by catching it directly with their mouths, rather than with their tongues.[17]
Hamilton's frog is a nocturnal ground-dwelling species. There is growing observational evidence that it may live in some trees as well.[3] It shelters in damp crevices during the day, and prefers rocks and boulders for survival.[3] They can be difficult to locate because of this night-time activity, plus they are well camouflaged, do not croak, and are very rare.
The community of Leiopelma hamiltoni that live on Maud Island are not evenly distributed throughout the rainforests. They typically live in much lower sections of the forest, around 300 meters above sea level, as there are more rocks and materials to hide in. Hamilton's frogs are a terrestrial species and are typically found in the coastal rain forests on this island or in deep boulder banks. They are nocturnal, so during the day they tend to reside in dark and damp crevices, which is why they are commonly found in and near boulder banks where they can hide under rocks and logs and stay deep under the canopy of the trees.[18]
The Hamilton's frog are insectivores. They feed on fruit flies, small crickets, moths, and springtails. Juveniles with a snout-vent length of 20 mm or less lack teeth, and thus are required to eat soft-bodied arthropods like mites and fruit flies.[19]
Leiopelma hamiltoni are insectivores and feed solely on insects, including crickets, flies, moths, springtails, and other small bugs. Their tongs are stuck to the top of their mouths, so they are unable to catch insects with their tongue like many other frog species do. Instead they have to catch prey with their mouths directly. Younger frogs have to eat small insects as they have smaller mouths with fewer teeth, so young Hamilton Frogs tend to eat mites and fruit flies.[20]
Females can lay between 11 and 15 eggs, which tend to be 9.6-9.6 mm in length.[9] They do not go through tadpole stages, but instead they develop totally within a gelatinous capsule in the egg, hatching out as froglets. They take around three years to reach maturity.[7]
Leiopelma hamiltoni breed in amplexus and fertilization takes place externally while the male and female frog are in contact with one another. They lay their eggs in cool, moist, areas on land, typically in depressions under rocks and logs. The eggs tend to stick together in clusters of around seven to nineteen. There are three layers to the eggs. These layers include an inner vitelline membrane, a gel like middle layer, and a protective coat on the surface.[21] The parents, but usually the males, will often seek out and find the site where they want to lay their eggs. They will then occupy and guard the site where they will lay eggs for weeks or sometimes months before the eggs are even fertilized. The species on Maud Island will typically lay their eggs in December each year. Once the eggs are laid, the male will stay with them, protecting them from any potential predators. The eggs take between 7–9 weeks to fully develop and hatch. Once they hatch, they do not immediately start swimming like most tadpole frog species. Instead, they climb onto their father's back and stay with him while they continue to develop there. They are very inactive while they are with the father, as he carries them around everywhere. After the frogs hatch, it takes them around 3–4 years to reach full maturity. During their development they have narrow fin tails and their hindlimbs develop first. Only their forelimbs are covered by the gular fold.[21]
This species of frog does not have any eardrums or earholes on the outside of its head, so they are unable to hear noises unless they are at an extremely low frequency. Since they can't hear, they use the odors emitted from its feces in order to communicate with other members. The chemical make up for each frog is slightly different, so the odor that comes from it is also distinct for each frog. This is how they can distinguish between relatives and how tell members of their species from potential threats. They also use the smell of their feces to claim territories and also ward off predators.[20]
Hamilton's frogs are not able to make a sound in order to communicate with each other or to ward off predators. However, when they are attacked, they can make a squeaking or chirping sound. This squeaking sound varies between individuals. The pitch of the squeak seemed to be inversely correlated with the size of the frog. Smaller frogs have higher squeaks. Also, temperature affects how long the frog will squeak for. In colder temperatures, they will squeak for longer amounts of time.[11] The squeaks are suspected of coming from forced expulsion of air from their lungs when startled, as they have no true voice box. Other than in the case of a predator attack, Leiopelma hamiltoni make no other sounds. If they are attacked, they will get into a stiff-legged stance and try to make themselves look as big as possible. They will extend their legs and raise their body, and then butt their heads. This head-butting, accompanied with the striped glands along its back, are components of an anti-predator defense adapted by terrestrial species. They will also emit a mal-tasting secretion from their granular glands if they are attacked to prevent a predator from eating it.[11]
Some predators of Leiopelma hamiltoni are New Zealand tuataras, which is a type of reptile, and black rats. The black rats that live on the island are non-native to the area the frogs live in and pose as a severe threat to their survival.[17]
Hamilton's frog can communicate with other frogs through chemical signaling through fecal smells.[22] This was determined in a 2002 study done where any other sensory signal was eliminated, so chemical signaling was the only response to the frogs’ behavior.[22] Fecal signals identified home territories.[22] This signaling can be used to determine if there is an intrusion into one's terriroty by another member of the species: the intruder will leave and retreat if it is smaller than the frog whose territory it inhabits.[22] Many anurans may use chemical signaling: even though several frogs use croaking and other auditory communication, chemical signaling may be important as an addition or even a substitute in quieter or silent species.[22] The frogs will strategically deposit feces in response to certain signals. These fecal signals alert others of home ranges and social status. Also, the feces signaling can ward off competitors and intruders. The feces typically will repel a comparator as long as the competitor is smaller than the individual who produced the feces. Also, feces repel individuals from farther locations better than local individuals. Therefore, size plays an important role in interactions and communications between Leiopelma hamiltoni. Size indicates how many resources an individual might have or how strong one might be. Size is an honest signal as there is a correlation between body size and metabolism and gland activity or dietary differences.[23]
Farming and deforestation on Maud Island has destroyed much of the land that the frogs used to live on, however they have managed to keep a stable number on their own in the cluster of land that they currently reside in. The frogs on Stephans Island are endangered however. They are at risk due to increase in predators, as species like the black rat have been introduced to the island. Much of their forest has also been destroyed, so they do not have much space to exist.[13] They are only able to reside at the very top of Stephans Island, as that is the only cluster of trees on the island. Conservationsists have tried translocating groups of these frogs to other areas, in hopes that they can prosper and reproduce in a different environment. They have also built a fence around the “frog bank” on Stephans Island to keep predators away.[13]
The Hamilton's frog two main predators are the native tuatara (Sphenodon punctatus) and the introduced black rat (Rattus rattus). Both of these two predators have caused the Hamilton's frog population to drop to less than 300. It is also vulnerable to the chytrid fungus (Batrachochytrium dendrobatidis).[19] Habitat loss is another large area of concern for this frog. Because they may span a wide variety of vertical spaces, both tree and ground are vulnerable areas that are subject to change and endanger Hamilton's frogs.[22]
In August 2018 the Department of Conservation (DOC) classified the Hamilton's frog as Nationally Critical under the New Zealand Threat Classification System.[2]
New Zealand has been protecting the Hamilton's frog species since 1921. A tuatara fence has also been built to stop tuataras from getting through. There is population monitoring also in place. There are plans to move some of the population to another island.[1]
The Hamilton's frog (Leiopelma hamiltoni) is a primitive frog native to New Zealand, one of only four extant species belonging to the family Leiopelmatidae. New Zealand's frog species all are in the family Leiopelmatidae. The male remains with the eggs to protect them and allows the tadpoles to climb onto his back where they are kept moist. It is named in honour of Harold Hamilton the collector of the type specimen. The holotype is in the collection of the Museum of New Zealand Te Papa Tongarewa.
