Maud Island's Old Timers

One of New Zealand’s four native frog species lives longer than any other frog in the world. David Brooks uncovers some surprising facts about the frogs found only on Maud Island in the Marlborough Sounds.

The sedentary lifestyle of  Maud Island frogs makes  them easy to study. Photo: Phil Bishop

The sedentary lifestyle of Maud Island frogs makes them easy to study. Photo: Phil Bishop

Maud Island frogs have changed little since the time  dinosaurs roamed the world. The endemic New Zealand species is the longest lived wild frog in the  world. But for its public profile it is a case of out of sight, out of mind.

Discovered in the 1940s on an island in Pelorus Sound in Marlborough, these tiny dark brown frogs have been regularly studied by scientists since the mid-1970s.

Associate Professor Ben Bell of Victoria University’s School of Biological Sciences has returned to the island to monitor the population at least once a year since 1982, leading efforts that have uncovered some remarkable facts.

“Maud Island stands out now as probably the world’s longest-run study of the longest-lived wild frogs,” Ben says.Maud Island frogs, Leiopelma pakeka, can live to about 40 years but from adulthood they can remain within an area just a few metres across for decades.

Ben say they will often find the same frog sitting near the same rock year after year.

“The oldest one I have been monitoring is called Xena and when I last caught her in May last year she was estimated to be 40 years old. Once they get to 35 years, we give them a name. Among the others we’ve also got ones called Wellington and Gollum,” he says.

The frogs grow to 50mm long and live under leaf litter covered rocks in a mature bush remnant. Their lifetime range extends to only about 30 square metres, with the centre of their range shifting by only 1.3 metres every 10 years.

They are unlikely to feature in a TV show about the world’s most fearsome predators – when they emerge in the evening to feed, they will sit placidly and wait for a spider, beetle or other invertebrate prey to walk by before pouncing.

Their sedentary lifestyle makes them particularly easy to study. “You can go out at night and just pick one up and then put it down in the same spot and it will just continue sitting there,” says Associate Professor Phil Bishop, the leader of the Otago University frog group.

Along with the other three surviving native New Zealand frogs, or pepeketua, Maud Island frogs are members of the Leiopelmatidae family.

When New Zealand was still part of the ancient super-continent of Gondwana, Leiopelmatidae split off from the branch that later developed into modern frogs.

“They diverged from the other lineage of amphibians 180 million years ago, so frogs very similar to Leiopelmawould have been hopping around the feet of dinosaurs. They are a very different frog from all other modern frogs,” says Phil.

If you have seen or heard a frog in New Zealand, it is almost certainly one of three introduced Australian species – brown tree frog, green and golden bell frog and southern
bell frog.

All our native frogs are found in relatively small numbers in isolated areas and their nocturnal habits, lack of regular calling and camouflage make them hard to find.

Unlike modern frogs, our native species lack an external eardrum and don’t make regular croaking sounds. They don’t have tadpoles.

Young froglets emerge almost fully formed from eggs and are carried around on the backs of their fathers until fully developed, apart from the semi-aquatic Hochstetter’s frog, which hatches at an earlier stage of development.

The Maud Island frog and the closely related Hamilton’s frog, which was also reduced to one small predator-free island in the Marlborough Sounds, would once have been found throughout most of New Zealand.

Like many of our other native creatures, they evolved without mammal predators and were decimated by rats, stoats and other pests after human settlement.

Although the numbers of frogs on Maud Island are fairly healthy at up to 40,000, the
danger of relying on one small island for the future of a species is obvious.

Disease or a natural disaster could easily lead to extinction if all the frogs were at one site.

A hundred frogs were transferred to another part of Maud Island in the mid-1980s and the population at the new site has since doubled. In the Marlborough Sounds another successful translocation took place to Motuara Island in 1997, followed by a less successful move to Long Island in 2006.

Phil says poor habitat and possible predation by kiwi – to which a small pioneer population might be vulnerable – may have been at the root of the Long Island failure.

Motuara’s habitat has been favourable and the frogs were initially surrounded
by a kiwi-proof fence.

Sixty frogs were also transferred to Wellington’s Zealandia fenced sanctuary in 2006 with
another 100 going there in December last year.

Of the initial transfer, 29 frogs were released into the open and the rest were placed
in enclosures. Those in enclosures did well and although there were fears the 29 in the open had all died – possibly predated by kiwi and mice – recent indications suggest that
some did survive.

The chytrid fungus has been responsible for dramatic population declines of frog species in the Americas, Australia and Caribbean. It may have also played a role in the dramatic fall in numbers of Archey’s frogs through disease in the Coromandel from the mid-1990s.

Our native species are thought to have some resistance to infection from the fungus but it remains a threat, particularly if a more virulent hybrid develops, Phil says.

Like other frogs, our native species need a moist environment to survive, and climate change poses a major long-term threat. “We really have got to think very carefully about their distribution in terms of climate change and whether they are in the best places for the future,” Ben says.

“Over the longer term, we may have to look at predator-free sites in areas such as Fiordland or South Westland because if the climate is going to get drier, more stress will be put on the frog populations.”

Although much has been learned about Maud Island frogs, Ben and Phil agree much more research is needed to strengthen conservation efforts. More needs to be learned
about their breeding behaviour, the chemical signals believed to be their main form of communication and why Archey’s and Hochstetter’s frogs have coped better with
predators than Hamilton’s or Maud Island frogs.

A higher public profile leading to pressure for more resources for saving our unique frogs would also help.

After all, their pedigree is just as long and distinguished as the more famous dinosaur age relic, the tuatara.

Global Decline

When 1400 scientists gathered at the first World Congress of Herpetology in Britain in 1989, many were saying the same thing: “I went to work on my frogs this year and I couldn’t find any.”

Otago University’s Phil Bishop says this set the ball rolling for research that confirmed there was an alarming worldwide decline in the populations of frogs and other amphibians, such as toads and salamanders.

In 2011 Phil was appointed chief scientist of the Amphibian Survival Alliance, a global
group aiming to arrest and reverse the disastrous decline.

Reports of falling frog numbers dated back to the 1950s in the United States, Puerto Rico and Australia.

Similar news of severe declines later came from Central and South America and, alarmingly, these included seemingly pristine areas.

Data from 936 amphibian populations across the world indicated the decline had been global since 1990.The reasons for the decline are still not entirely clear but they are likely to be a combination of habitat destruction, pollution, predation and disease, climate change, an increase in UV radiation, over-exploitation and the global pet trade.

Phil says the alliance will soon launch a new initiative called Leapfrog as part of efforts to get more public engagement in the crisis facing frogs and other amphibians. “Our major initiative is going to be land purchase, buying areas of high amphibian diversity to make sure they’re not turned into shopping centres and things like that,” he says.

Three surviving relatives

There were at least seven native New Zealand frog species until about 1000 years ago but now only Maud Island frogs and three others remain because of the impact of humans
and the predators they brought with them. 

Hochstetter’s frog (Leiopelma hochstetteri) is the most widespread of the remaining species and is found in at least 10 populations scattered in the upper half of the North Island, including the central North Island, Coromandel, Great Barrier Island and the Raukümara Ranges, north of Gisborne.

Unlike the other New Zealand frogs, they are semi-aquatic and shelter during the day near
the edge of streams. The species also differs in being stockier in build, having
partially webbed feet and its mostly dark brown skin appears more warty than the others.

Archey’s frog (Leiopelma archeyi) is found only in the Coromandel and the Whareorino Forest, west of Te Küiti. It is the smallest of our native frogs, growing up to 38mm long and lives in moist native forest at an altitude between 400 and 1000 metres.

Observations by Ben Bell and his research team showed a dramatic 88 per cent decline in their numbers between 1996 and 2001, with disease being the most likely cause.

Numbers have since steadied but remain low and the species is ranked as critically endangered by the IUCN.

Hamilton’s frog (Leiopelma hamiltoni) is one of the world’s most endangered frogs, with
about 300 on Stephens Island in Cook Strait.

It is very similar to the Maud Island frog and its status as a separate species is being reconsidered but it differs from its close relative in being slightly smaller with some
differences in colouration.

If you find any native frogs, please leave them in peace but report their location to
your local DOC office. Climate change will put more stress on populations of Maud Island
and other native frogs

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