NEW ZEALAND FROGS: Leiopelmatidae

PHYSICAL CHARACTERISTICS

New Zealand frogs are rather small creatures that have wide heads with large eyes and round pupils, but no showing eardrums. They have little or no webbing between the toes on their front or hind feet. Their four feet also have smooth soles, a feature that sets them apart from similar species living in New Zealand, which have pads or suckers on their feet. New Zealand frogs are usually brown, but some are green or reddish brown. Most have dark brown to black patterns on their legs and backs. Lines of raised bumps on their backs and other small bulges on their bellies, legs, and/or feet hold poison. These bumps are called granular (GRAN-yoo-ler) glands. When a predator bites one of these frogs, the poison in the glands oozes out, which may cause the predator to spit out the frog, and possibly learn to leave the frogs alone in the future, too.

New Zealand frogs grow to 0.8 to 2 inches (2 to 5.1 centimeters) long from the tip of the head to the end of the rump.

GEOGRAPHIC RANGE

Although they share New Zealand with a few other species of frogs, the members of this family are the only frogs that are actually native to New Zealand. Humans introduced, or brought in, the others, which include two species of bell frogs and a brown tree frog. New Zealand frogs live on North, Maud, Great Barrier, and Stephens Islands. Conservationists in 1997 introduced one of the four species to Motuara Island, where it is surviving.

HABITAT

Most New Zealand frogs live in damp, forested areas, where they often hide during the day under rotting logs or loose stones. Some also survive among rocks and shrubs in a misty but almost treeless part of Stephens Island. Of the four species, Hochstetter's frog prefers the wettest environment, often living near streams or other bodies of water.

DIET

These small frogs eat insects and other invertebrates (in-VER-teh-britts), which are animals without backbones, that live in their habitat. Many species of frogs capture their prey by flinging out their long tongues and using them to grasp. New Zealand frogs, on the other hand, cannot stick out their tongues. Instead, a New Zealand frog must quickly lunge at a prey animal and grab it with its mouth.

BEHAVIOR AND REPRODUCTION

Most people, including the native people who have lived near them for thousands of years, are completely unaware of these quiet little frogs. New Zealand frogs make almost no noise. They may offer a soft squeak if they are roughly handled or some faint squealing sounds during the mating season. Otherwise, they remain silent and even stop moving if a person or some other possible predator comes close. These behaviors, combined with the frogs' camouflage colors and patterns, hide them from all but the most careful observers. In addition, these frogs are mostly nocturnal (nahk-TER-nuhl), which means that they are active at night. The darkness also helps to hide the frogs from sight.

THREE RECENT EXTINCTIONS

Fossils scattered throughout New Zealand show that it once was home to many frogs—all in the family Leiopelmatidae. These frogs, which have the fitting common name of New Zealand frogs, included three species that lived on the islands until 1,000 to 2,000 years ago, when they became extinct. Today, four species from this family still exist in New Zealand, but they live in very small areas compared to the land the family once called home.

Sometimes, however, predators are still able to find them. If the frogs have the chance to escape by jumping into the water, they will. They swim by kicking one leg at a time instead of kicking both hind legs together, as other frogs do. If they cannot escape a predator, three of the four species defend themselves by raising up on their four legs so they are as tall as possible and turning their bodies to face the predator. This puts forward their largest poison glands, those located in long bumps or ridges behind each eye, so that the attacker's first chomp is a mouthful of bad-tasting poison. Hochstetter's frog does not raise up its body as a line of defense, because its poison glands are on its belly not on its back.

During mating season, most species of frogs find one another by either making loud calls, in the case of the males, or responding to those calls, as the females do. Since New Zealand frogs do not call and even lack a real voice box, scientists think that they find each other by their smells instead. The female lays five to 20 eggs, depending on the species. The developing frog is visible inside the see-through egg capsule. Hochstetter's frog lays its eggs at streamside, and the animals go through a short tadpole stage before becoming frogs. The other three species—Archey's, Hamilton's, and Maud Island frogs—all lay their eggs on land, but under rotting logs or in other moist spots. These frogs go through their tadpole stage while still inside the eggs, so the eggs hatch right into tiny frogs. The male in all three of these species stays with the eggs until they hatch, often covering them with his body. He continues to protect newly hatched young by letting them climb onto his back and legs. Male Hochstetter's frogs do not care for their young.

NEW ZEALAND FROGS AND PEOPLE

As people have developed the land in New Zealand, these frogs have had to survive in smaller and smaller areas. Strict laws are now in place to protect the frogs and the places they live.

JURASSIC FROGS

Scientists are especially interested in New Zealand frogs because they have some very primitive features, including extra backbones and muscles that are designed to move tails. Since the frogs have no tails, scientists believe the tail-wagging muscles are left over from long-extinct ancestors of these species. The only other living frogs with these features are frogs of the family Ascaphidae. The extra backbones are also seen in fossils from the first frogs to live on Earth. The fossils date back to about 150 million years ago, which means the frogs shared the planet with dinosaurs.

CONSERVATION STATUS

According to the World Conservation Union (IUCN), all four species in this family are in danger. The most at-risk species is Archey's frog, listed as Critically Endangered, which means that it faces an extremely high risk of extinction in the wild. They were once much more common, but when scientists counted them in 1996 and again in 2002, they found that their numbers fell by 80 percent: four out of every five frogs had disappeared. In one population, the number of frogs went from 433 individuals to just 53. The cause of the drop was probably disease, possibly caused by a fungus. Scientists first became aware of the fungus, called chytrid (KIH-trid) fungus, in Australia and Central America in 1998 and have since blamed it for the declines of many frog species. They think an introduced species, called the Australian bell frog, brought the fungus to New Zealand and passed it on to Archey's frog in about 1998. The fungus is still a problem. When the fungus infects one of these frogs, it has trouble moving and soon becomes paralyzed.

The IUCN considers Hamilton's frog to be Endangered, which means that it faces a very high risk of extinction in the wild. The remaining two species, Maud Island and Hochstetter's frogs, are Vulnerable and face a high risk of extinction in the wild. The major threats to these species are introduced predators, including rats and ermines, which are in the weasel family, and the lizard-like tuataras. In some cases, conservationists are trying to build barriers around the frogs' habitats so the predators cannot reach them. In addition, scientists are keeping a watchful eye on these three species to see if the chytrid fungus eventually affects them, too.

HAMILTON'S FROG (Leiopelma hamiltoni): SPECIES ACCOUNTS

Physical characteristics: Hamilton's frog is usually light brown with a single dark stripe running along each side of the head and through the eye. It also has a noticeable ridge running from the head down each side of the body. Its feet have no webbing between the toes. The frog grows to 2.0 inches (5.1 centimeters) long from snout to rump. Females are usually a bit larger than males.

Geographic range: One of the rarest frogs in the world, it lives in a tiny area high atop Stephens Island in New Zealand.

Habitat: Although its preferred habitat is likely moist forest, this species now survives in a damp, rocky pile that is covered mostly by grasses and shrubs.

Diet: Hamilton's frog eats insects and other invertebrates.

Behavior and reproduction: This frog, for the most part, remains out of sight during the day. Like the other New Zealand frogs, it does not call. It can, however, squeak if mishandled. Females lay five to nine eggs at a time on land. Each egg hatches into a tiny frog. The males watch over the eggs and young.

Hamilton's frogs and people: Humans rarely notice this quiet frog.

Conservation status: The IUCN considers Hamilton's frog to be Endangered, which means that it faces a very high risk of extinction in the wild. Protection efforts are under way to protect its small home area and to help it survive into the future. ∎

MAUD ISLAND FROG (Leiopelma pakeka): SPECIES ACCOUNTS

Physical characteristics: The Maud Island frog looks so much like Hamilton's frog that scientists thought they were the same species until 1998. At that time, they compared their DNA and found that the frogs were different enough to be separated into two species. DNA, which is inside the cells of all animals, is a chain of chemical molecules that carry the instructions for creating each species and each individual. When looking at the frogs from the outside, the biggest difference between the two species is their color: the Maud Island frog is paler, but only slightly. They both have unwebbed feet and ridges on the back, and each grows to 2.0 inches (5.1 centimeters) long from snout to rump. Females are a bit larger than males.

Geographic range: It lives on a tiny scrap of land, measuring just 0.06 miles² (0.15 kilometers²) on Maud Island in New Zealand. In 1997, conservationists gathered 300 individuals and transplanted them to Motuara Island, where the frogs seem to be surviving well.

Habitat: This frog makes its home in the forest that covers the east side of a hill on Maud Island. Although the forest reaches up the hill to about 980 feet (300 meters), the frog tends to live in the lower portion, where the slope is flatter and the climate is more moist. This species often hides among rocks and logs.

Diet: It eats insects it finds in its habitat.

Behavior and reproduction: The Maud Island frog stays out of sight during the day and comes out at night to hop slowly about and look for food. Female Maud Island frogs lay their eggs, which can number up to 20, in damp spots on the forest floor. Each male watches over his eggs until they hatch into tiny frogs. He allows the froglets to climb up his legs and onto his back.

Maud Island frogs and people: Humans rarely see this nighttime frog.

Conservation status: According to the World Conservation Union, the Maud Island frog is Vulnerable, which means that it faces a high risk of extinction in the wild. The current major threat to this species is introduced predators, including rats and ermines. Efforts are under way to keep the predators away from the frogs. Additional efforts proceed to protect and restore the frog's tiny habitat on Maud Island and to introduce the frog to a new area on Motuara Island. ∎

FOR MORE INFORMATION

Books:

Grigg, G., R. Shine, and H. Ehmann, eds. The Biology of Australasian Frogs and Reptiles. Chipping Norton, Australia: Surrey Beatty and Sons, 1985.

Hutching, Gerard. The Natural World of New Zealand: An Illustrated Encyclopaedia of New Zealand's Natural Heritage. Auckland: Penguin, 1998.

Jones, Jenny. Hamilton's Frog. Auckland: Heinemann Education, 1994.

Robb, Joan. New Zealand Amphibians and Reptiles in Color. Auckland: Collins Publishers, 1980.

Web sites:

Barnett, Shaun. "The Trouble with Frogs." Forest and Bird Magazines.http://www.forestandbird.org.nz/magazines/00Feb/frogs.asp (accessed on January 20, 2005).

"Frogs." Christchurch City Libraries. http://library.christchurch.org.nz/Childrens/FactSheets/Animals/Frogs.asp (accessed on January 28, 2005).

Kingsley, Danny. "Ancient Frogs Threatened by Fungus." ABC Science Online.http://www.abc.net.au/science/news/enviro/EnviroRepublish_537533.htm (accessed on January 20, 2005).

Lehtenin, R. "Leiopelmatidae." Animal Diversity Web.http://animaldiversity.ummz.umich.edu/site/accounts/information/Leiopelmatidae.html (accessed on January 20, 2005).

"Native Frog Facility to Open at Auckland Zoo." Scoop.http://www.scoop.co.nz/mason/stories/AK0410/S00129.htm (accessed on January 20, 2005).

"New Zealand Ecology: Living Fossils." TerraNature.http://www.terranature.org/living_fossils.htm (accessed on January 20, 2005).

"Welcome to the New Zealand Frog Survey (NZFS)!" University of Otago. http://www.otago.ac.nz/Zoology/frogs/#nz%20species (accessed on January 20, 2005).