Archey's Frog (Leiopelma archeyi)

The Archey's frog (Leiopelma archeyi) is one of the world's oldest and most primitive frogs. Found in three locations on the North Island of New Zealand, it is New Zealand's only terrestrial frog. It prefers moist forests at an elevation of about 400 to 1,000 meters above sea level but has been known to live at lower elevations of 100 to 200 meters above sea level. A nocturnal frog, it stays under stones and logs during the day. It eats small insects, arachnids and other invertebrates.

With a maximum length of thirty-seven millimeters, it is the smallest frog native to New Zealand. Its mottled green, red and brown skin provides camouflage. It has about six rows of defensive granular glands down its back and sides, as well as the backs of its legs, feet and sometimes arms.

The Archey's frog has several unique characteristics. It has round eyes, webless hind toes and tail-wagging muscles despite losing its tail. It lacks the vocal sac and eardrums common to other frogs. Rather than croaking, it squeaks or chirps when mating or disturbed. It has a poison gland in its head that makes eating the head fatal to predators. It also has rib-like pieces of cartilage in its abdominal muscles and nine vertebrae instead of eight.

The female lays a clutch of eggs in a cool, moist spot beneath fallen trees or rocks. The male frog watches over the eggs. Froglets hatch semi-developed—with tails, small arms and legs—and do not undergo a tadpole stage. They climb onto their father's back and stay there for five to six weeks until they finish developing. They mature in three or four years and reproduce around fifteen years. Archey's frogs can live as long as thirty years.

Background

Archey's frog is one of four ancient species of frogs found in New Zealand. At one time there were at least seven prehistoric species, but three species died out after Polynesian settlers arrived in the thirteenth century. These ancient species of frogs belong to the family Leiopelmatidae, which evolved more than 200 million years ago. Archey's frogs began inhabiting what is now New Zealand about 80 million years ago, before it separated from the supercontinent Gondwana. The other three surviving species are Hamilton's frog, the Maud Island frog and Hochstetter's frog. These species are considered living fossils because they are similar to 150-million-year-old fossils from the late Jurassic period that were found in Queensland, Australia. The fossils show the living species have not changed significantly in millions of years and closely resemble their ancient ancestors.

Centuries ago Archey's frog likely had a wider range on North Island than its current distribution. By the time it was identified as a separate species in 1942, it was found in just two locations: a large population on Coromandel Peninsula and a smaller population in the Whareorino Forest. After the first human settlers arrived in New Zealand, the introduction of non-native predators, especially rats, and habitat loss reduced the range and populations of Archey's frogs.

From 1996 to 1998 the population of Archey's frogs in the central Coromandel Range declined steeply. A field survey in December 1996 showed a formerly large population group on Tapu Ridge had declined significantly. Researchers recorded an 88 percent decline in population size in the Coromandel Range between 1996 and 2001. Although the cause of the sudden steep decline of Archey's frogs is unknown, scientists suspected a fungal skin disease, chytridiomycosis. Other possible causes included drought, habitat disturbance by researchers, pesticides, poaching and introduced predators, such as rats. In 2001 scientists confirmed the amphibian chytrid fungus in Archey's frogs, verifying it was responsible, at least in part, for their decline. Scientists, however, suspect it was not the sole reason and continue to investigate the decline to better identify its causes.

In 2004 the International Union for Conservation of Nature and Natural Resources listed Archey's frogs as critically endangered due to their significant decline of population. In 2006 researchers translocated seventy Archey's frogs from Whareorino Forest to Pureora Forest Park. The group managed to survive, and another sixty frogs were translocated in 2016.

Archey's Frog Today

The total population of Archey's frogs is unknown. In 2013 University of Otago zoologist Phillip J. Bishop and ecologists at the New Zealand Department of Conservation (DOC) estimated the adult population at between 5,000 and 20,000. Whereas the Coromandel Range formerly had the largest population, its total population remains low—around its 2002 level of 53 frogs—but stable. Population groups are larger and denser in the Whareorino sites.

The DOC is responsible for the conservation management of Archey's frogs, which focuses on population monitoring, disease surveillance, research, captive breeding and invasive predator control programs, such as bait stations. The Auckland Zoo assists the DOC with its annual field surveys and has established a breeding program for Archey's frogs. It hatched and raised a group of frogs between 2012 and 2013. The zoo continued to breed captive Archey's frogs throughout the 2010s.

The DOC, the Carter Holt Harvey Native Frog Research Centre at Auckland Zoo and researchers at Otago, Victoria and Massey Universities are working together to cure chytrid fungal infection and to prevent its spread and minimize its threat to Archey's frogs. Researchers are also investigating other potential threats to Archey's frogs. In 2023, a study showed that sustained rat control had a promising impact on Archey's frog populations over twelve years.

Bibliography

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"Archey's Frog." New Zealand Department of Conservation, New Zealand Government, www.doc.govt.nz/nature/native-animals/reptiles-and-frogs/frogs-pepeketua/archeys-frog. Accessed 17 Jan. 2025.

"Archey's Frog (Leiopelma Archeyi)." Evolutionary Distinct & Globally Endangered, www.edgeofexistence.org/amphibians/species‗info.php?id=546. Accessed 17 Jan. 2025.

Chih Wang. "Leiopelma Archeyi: Archey's Frog." Edited by Ann T. Chang, Amphibia Web, U of California, Berkeley, 5 June 2013, amphibiaweb.org/species/2064. Accessed 17 Jan. 2025.

IUCN SSC Amphibian Specialist Group. "Leiopelma Archeyi." The IUCN Red List of Threatened Species 2017, International Union for Conservation of Nature and Natural Resources, 2017, dx.doi.org/10.2305/IUCN.UK.2017-3.RLTS.T11450A66654575.en. Accessed 17 Jan. 2025.

Judd, Warren. "The Truth about Tadpoles and Frogs." New Zealand Geographic, no. 38, Apr.–June 1998, www.nzgeo.com/stories/the-truth-about-tadpoles-and-frogs. Accessed 17 Jan. 2025.

NZ Frog. New Zealand Frogs Research Group, www.nzfrogs.org/NZ+Frogs.html. Accessed 17 Jan. 2025.

White, Rebekah. "A Leap in the Dark." New Zealand Geographic, no. 145, May–June 2017, www.nzgeo.com/stories/a-leap-in-the-dark. Accessed 17 Jan. 2025.