Hamilton's Frog (Leiopelma hamiltoni)
Hamilton’s frog is one of the rarest frogs in the world, with a population of less than 300 animals. Fossil records show it was once spread from Waikato to Punakaiki, but now it is only found on a small area of rocky ground on the summit of Stephens Island in the Cook Strait. Being adapted to live on rocky ground, the hind feet have almost no webbing. Grows up to 50mm long, larger than both
L. hochstetteri and
L. archeyi. Recent conservation measures have resulted in a number of frogs being translocated to one of the inner Chetwode Islands. The IUCN lists this species as Endangered. There is no webbing on their feet or hands. They are very similar to
Leiopelma pakeka and up until recently they were thought to be the same species. However, in 2001 scientists using molecular techniques, found little variation between the two taxa and although favor keeping them as one species, they suggested treating them as 'evolutionary significant units'. They look almost identical to
Leiopelma pakeka but are slightly larger. This species and the Maud Island frog (
L. pakeka) are monomorphic (i.e. both sexes look alike) and therefore very difficult to sex in the field. Breeding has not been observed in the field for either of these species.
Maud Island Frog (Leiopelma pakeka)
These frogs are relatively large (also up to 50mm long), and are generally dark brown. Until recently, they were only found on Maud Island in the Marlborough Sounds; however, some
L. pakeka have been translocated to several other predator-free islands in the Marlborough Sounds. The latest estimate of the number of individuals of this species is around 40,000.The IUCN lists this species as Vulnerable, although it is listed as Nationally Endangered.
They are nocturnal and catch their prey by grabbing it with their mouth as they do not flick their tongues out like many other frogs. Although these frogs have never been observed breeding in the wild, Dr Ben Bell of Victoria University has made some observations from an outdoor enclosure. He discovered that in captivity frogs lay 1-19 eggs in December in moist depressions under logs, rocks or vegetation. The eggs are guarded by the male and take 14-21 weeks for the eggs to develop. There is no free-swimming tadpole stage and the young climb onto the dorsal surface of the male and continue their development there. During this time they remain fairly inactive.
These frogs prefer cool misty evenings and are particularly active above ground when the temperature is between 8 and 14C. They show considerable site fidelity and tend to stay with a 5m radius for years at a time. They are very long lived with some individuals being found thirty years after they were marked.
Archey's Frog (Leiopelma archeyi)
Archey’s Frog
Leiopelma archeyi (CR) is the smallest of the indigenous species (<38 mm). They are restricted to two regions on the North Island of New Zealand, occurring on the Coromandel Peninsula and the Whareorino Forest, west of Te Kuiti. In both of these areas, it occurs sympatrically with
Leiopelma hochstetteri. They prefer to live at a relatively high altitude from about 400-1000 m in moist native forest; they are terrestrial and nocturnal, spending most of the day hidden under stones or logs away from streams or creeks.
Leiopelma archeyi is a terrestrial breeder, laying a small clutch of eggs in a moist site under stones or logs. They exhibit parental care with the tailed froglets remaining on their father’s back for several weeks until metamorphosis is nearly complete. Populations of this species have crashed in recent years with monitored populations decreasing by 88% over the 1996-2001 period.
Several factors, including the severity and rapidity of the population crash, the geographic spread of the decline (from south to north), and the discovery of frogs with chytridiomycosis (caused by
Batrachochytrium dendrobatidis), all point to disease being the major cause of the decline. A breeding facility has recently been opened at Auckland Zoo with the intention of producing a self-sustaining captive population. A top priority of the New Zealand Native Frog Recovery Group is to investigate ways of preventing further declines of this species.This frog is listed as Critically Endangered by the IUCN.
Hochstetters Frog (Leiopelma hochstetteri)
Hochstetter’s Frog
Leiopelma hochstetteri (VU) is the more aquatic frog (albeit semi-aquatic) of the four living species. It is widely distributed in at least 10 fragmented and isolated populations in the northern half of the North Island. They are nocturnal and shelter by day in wet crevices or under stones or logs close to the water’s edge in shaded streams. Males of this species exhibit sexual dimorphism in the form of more muscular, robust forelimbs than females. This is another distinctive trait, as the other three
Leiopelma species are not sexually dimorphic, apart from females reaching greater body size. One of the main threats to this species is the destruction and modification of its habitat, which is still occurring either directly (e.g. afforestation, gold mining, storm water discharge) or indirectly (e.g. feral goats and pigs causing erosion leading to stream siltation). The New Zealand Department of Conservation has purchased considerable amounts of suitable land to prevent further degradation of some of their habitat, and attempts are being made to better monitor their populations. This frog is listed as Vulnerable by the IUCN.
