Leiopelma hamiltoni

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. (Newman, 1990; Tocher, 2010; Wang, 2003; "Hamilton's Frog (Leiopelma hamiltoni)", 2007)

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.

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. (Wang, 2003; "Animal Fact Sheets: Hamilton's Frog (Leiopelma hamiltoni)", 2006)

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. (Bell, 1978; "Animal Fact Sheets: Hamilton's Frog (Leiopelma hamiltoni)", 2006)

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. (Bell, 1978)

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. (Bell, 1978; Wang, 2003)

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. (Bell, 1978; "Hamilton's Frog (Leiopelma hamiltoni)", 2007)

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. (Bell, 1994)

These frogs do not exhibit any migrational behavior, and it is unknown whether they prefer living in social groups. The entire population lives in close proximity to one another, but this is largely due to habitat availability and does not give any indication to social preferences. (Burton and Burton, 2002)

Hamilton's frog is nocturnal. It emerges at nightfall, and is usually most active on rainy nights with high relative humidity. (Newman, 1990)

No information is available regarding home range for Hamilton's frogs.

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. (Bell, 1978; Wang, 2003)

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. (Lee and Waldman, 2002)

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. (Meyer-Rochow and Pehlemann, 1990)

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. (Bell, 1994; "Animal Fact Sheets: Hamilton's Frog (Leiopelma hamiltoni)", 2006)

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. (Peeling, 2005; Tocher, 2010)

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. (Tocher, 2010; "Animal Fact Sheets: Hamilton's Frog (Leiopelma hamiltoni)", 2006)

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 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. (Tocher, 2010)