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. 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.
Despite being New Zealand's largest extant native frog, Hamilton's frog is a small species when compared to frogs from around the world, with males reaching a total length of up to 43 mm and females being larger at 52 mm. 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. There is no webbing between the hind toes, and the fingers are not webbed.
Hamilton's frog survive 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. They live around rocky, moist and grassy areas.
Hamilton's frog is a ground-dwelling species that is nocturnal. It shelters in damp crevices during the day. They can be difficult to locate because they are well camouflaged, nocturnal, do not croak and are very rare. 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. 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.
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 ).
In August 2018 the Department of Conservation (DOC) classified the Hamilton's frog as Nationally Critical under the New Zealand Threat Classification System.
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.
