This Is How It Ends: All creatures great, small and vanishing

Wednesday, 20 October 2021

We can’t see them, and they give us the heebie jeebies. But some of our most invisible endangered species are significant indicators of the health of our natural environment. Andrea Vance and Iain McGregor report, for Stuff’s This is How it Ends series.

Bats get a bad rap.

Associated with eccentricity or absent-mindedness: “bats in the belfry” or “batty”. Linked to nocturnal behaviour and dark, often cold places such as caves and mines. A mystical connection to bloodsucking Count Dracula, or hokioi, a bird which foretells death. And blamed for the spread of disease, such as rabies and more recently Covid-19.

But their reputation is undeserved.

They are vital, not only to the environment, but to humans.

Without pollinating and seed-dispersing bats, plants would fail to provide food and cover for species at the bottom of the food chain, causing entire ecosystems to deteriorate.

Once common in forests throughout New Zealand, bat range became restricted by felling, and colonies were attacked by introduced predators, rats, stoats and cats.

There are two species of bats in New Zealand: the long-tailed bat and the lesser short-tailed bat, and they are its only land mammals.

There were once two species of short-tailed bats, but the greater short-tailed bat is probably extinct. The lesser short-tailed bat is found only at a few scattered sites, and is divided into the northern, central and southern subspecies, discerned by their location.

“The short tail bats are important pollinators and seed dispersers,” says Colin O’Donnell, principal science advisor for the Department of Conservation.

“They eat nectar and certain flowers and pollinate them. There's some special plants that really rely on bats to be their primary pollinators.

“They eat lots of insects, as well. It's well-known, from overseas studies, bats can control insect numbers, to a degree. Long-tailed bats, which feed on the edges of forests, are good consumers of insect pests.

“They love grass scrub beetles [and] purini moths, which are two big agricultural pests.

“So, if we could recover their numbers then they would be free insecticides.”

The chestnut-furred long-tailed bat is classed as ‘nationally critical,’ the highest threat ranking, and the short-tailed bat subspecies range from ‘nationally vulnerable’ to ‘recovering’.

But the mousy-grey short-tailed bat is especially precious as the only remaining species within its family.

O’Donnell is New Zealand’s bat man – and yes, he’s heard that joke many times before.

He’s worked with the mammals here and internationally for more than 25 years, and is also an expert on forest and wetland birds, lizards, the impacts of predators, and conservation management to reverse population declines.

Each summer he pitches a tent in the beech forests of Fiordland’s Eglinton Valley, one of the only South Island sites with both species.

“Since the mid-90s, we've been monitoring bats here. We're here for six weeks, just after New Year, when the babies start flying.

“We count their numbers as they come out of their colonies at night. And we tag them and look at survival over time.”

New Zealand’s bats are special: they live in trees, not caves.

“When I first came down here, I thought: ‘I'm going to find the Bat Cave, and we can protect it from the predators, study the bats and monitor them nicely’.

“And the first thing I discovered was that they didn't use caves at all. They live in cavities in trees, and quite often they are 25-30 metres up, which makes them really challenging to find and study.”

It also makes them vulnerable to introduced predators. “The first 10 years, it was a bit depressing, because each year, the numbers were declining. We determined predators, like stoats and rats, were killing the bats.

“Because bats live in tree hollows, when a predator runs up the trunk and pops its head in, there's no escape for the animals inside. They get killed in large numbers.”

Using infra-red cameras, O’Donnell estimated there were 300-400 short-tailed bats left in the valley, and three colonies of long-tailed bats.

“One of those colonies all but disappeared in 1999-2000, when the beech was seeding really heavily and the rat and stoat numbers built up. A second colony declined to just 24 breeding females. We were getting quite close to extinction.

“After that, DOC started doing more extensive predator control. And over the last 15 years or so, we've been monitoring a steady increase in numbers. A depressing project became quite an exciting one.”

The short-tailed bats are increasing by about 8 per cent a year in the valley, with long-tails increasing by 4 per cent each year.

Elsewhere, the picture is mixed. In Pureora Forest Park, west of Lake Taupō, predator control has allowed the population of short-tailed bats to grow by 10 per cent annually. There are about 300 in a protected colony in Wairarapa, and a population at Ettrick Burn in Fiordland’s Murchison Mountains.

Once so common they roosted under bridges along the river Avon, long-tailed bats appear to be declining in the Pureora Forest, but can be seen in South Canterbury and more recently have been detected in Hamilton, Auckland and Tauranga.

Catching one isn’t easy. Long-tailed bats weigh only 8-10g and fly at up to 60kmh. Short-tailed bats fly at 40kmh and are slightly heavier at 12g-15g. Unlike most bats, which snag their prey in the air, short-tails forage on the forest floor, folding their wings into ‘limbs' for scrambling around.

Because they use echolocation, conventional nets used for trapping birds are useless.

“A bat navigates in the dark using sonar, flying around, shouting its head off and calls echo off the environment around them,” O’Donnell says. “If you’re a bat you fly around at 40kmh an hour and catch a sand fly without banging into a tree. So they can detect pretty much anything: a bat flying up to a mist net is like a brick wall to them.”

A harp trap – a frame supporting two rows of fine thread, and a catching bag at the base – captures them without damaging their delicate wings.

O’Donnell also uses a high frequency speaker, emitting bat calls, to lure the animals, which are deeply social. Once caught in the plastic liner, the bats cuddle up together until they are handled by researchers.

“They crawl up in the corner and go to sleep once you've caught them, so they're really quite chilled animals to catch.”

Before first light, O’Donnell’s team measures, weighs and gives the creatures a health check. They are fitted with metal bands, and if they are the correct size, minuscule tracking devices.

It is crucial to keep them warm and release them before day breaks – otherwise they must be tucked into cloth bags and hung in an airing cupboard in a bedroom back at the Knobs Flat base. Of course, it’s known as ‘the Bat Cave’.

The bats don’t hibernate in winter, but survive by dropping their temperature, slowing heartbeats, and sleeping for up to 10 days to conserve energy. “It's barely alive, but it is very alive,” O’Donnell says.

“When it snows here, it can be minus 13 for two weeks in the mornings. And they'll just curl up and go to sleep. Then, when there's a sunny, warm day and nice evening, they'll suddenly wake up again, raise their body temperatures back up and fly off and feed.”

O’Donnell is beguiled by the flying mammals. “There's lots of things that fascinate me. They only have one baby a year, really slow breeders, but they live for a really long time.

“Our oldest long-tailed bat here is at least 25 years old. That's remarkable for such a tiny animal.

“And they're essentially a huge kite with a little body in the middle. They can fly a long way, really fast, for their size.”

But there is one mystery he cannot solve. “The really irritating thing is they move to a new tree cavity virtually every day. And for the life of me, I can't figure out why they do that.

“Each colony has got maybe 180-200 different trees, and they cycle around, moving daily to the next one. They do it in a real set sequence, so you can almost predict which roosts they're going to be in on which day. I can't really think of a logical reason for that except for: they can.”

Forests are biodiversity magnets. When we think of their wildlife, we look up to the birds and bats in the canopy. But there is a secret life dwelling in the leaf litter below the trees.

Before humans arrived, the mossy forest floor was once alive with frogs. Now, only four of seven native species survive, disappearing entirely from the South Island and lower North Island.

Hochstetter's frog/pepeketua, of which there are believed to be about 100,000, live in isolated fragments around Waitakere and Hunua Ranges, Dome Valley, Coromandel Peninsula, Great Barrier Island, Sanctuary Mountain Maungatautari, and the East Cape. They prefer streams but can survive on land.

In Cook Strait, fewer than 200 Stephens Island frogs cling to a 600sqm patch of bare land, and nearby 19,000 Maud Island frogs survive.

All four frogs evolved from one ancient genus (a category ranks above species and below family). They are small, do not croak, and hatch as tiny froglets, rather than free-swimming tadpoles.

The smallest of the endemic species is the 2-3cm-long Archey's frog, now limited to Waikato, and is one of the world's rarest and most endangered amphibians.

Auckland Zoo manages a breeding programme and assists DOC with annual surveys in Whareorino Forest, near Te Kuiti.

Richard Gibson is head of animal care and conservation.

“They're one of the most extraordinary frogs in the world. There are thousands of frog species. And Archey's frogs hold the dubious title of ‘No 1 edge frog’. It’s an acronym for evolutionary distinct, and globally endangered.

“The evolutionarily distinct part of it is that they are very primitive. They've been around since the time of the dinosaurs, like the tuatara or even giant wētā. Sometimes people call them living fossils because of their antiquity.”

They live for up to 40 years, and stay faithful to small areas of habitat.

“The [four endemic] frogs are all threatened, and the threats are loss or disturbance of habitat, [and] introduced mammalian and avian predators. And now, as we face climate change, and less frequent and reliable rainfall, which impacts on the humidity of the forest, which is essential for amphibians.”

Like many of New Zealand’s unique creatures, Archey’s have quirks.

“They're on their own branch of the evolutionary tree. They have little tails, little muscles retained in their pelvis for wiggling a tail that they no longer have.

“They're not very good at jumping. They jump and just crash-land on their faces because jumping is not something they evolved to do. They have inscriptional ribs, little floating ribs in their bellies that all other amphibians have lost. There's a lot of morphological oddities around the New Zealand frogs.”

And there are behavioural traits.

“Archey's frogs reproduce terrestrially, in a little hollow on the ground. The female has done her work, and she'll disappear off into the forest whereas the male will guard those eggs for weeks on end.

“He's probably protecting them from predators by his presence. We know he urinates on them, probably maintaining moisture. And skin secretions of the male Archey's frogs may have antifungal or antibacterial properties, which make sure the eggs stay healthy during development. This is all still being studied.”

Once hatched, the froglets spend another month or so clinging on to dad's back while they fully develop their legs.

Amphibians are known as ‘indicator species’, because they are extremely sensitive to changes in the environment and give insight into how an ecosystem is functioning.

Globally, populations have declined at an unprecedented rate, with up to 200 species vanishing since 1980. About one-third are threatened with extinction.

“People often ask, if we were to lose Archey's frogs, the other frogs, why does it matter?” Gibson says.

“Everything has a place in an ecosystem. Archey's frogs are prey items, and they're also predators of smaller prey, invertebrates is what they eat. So they play an important part in a food web.

“Of course, we shouldn't let any animal go extinct. We're the only species on the planet rampaging around and causing negative impacts to all the other species that call this planet home. We have no more right to be here than any of them.

“We have a duty to minimise that harm, start righting some of the wrongs, and making sure we value all species for their intrinsic value, for what they are. These are our precious taonga of New Zealand, and they deserve to be, and must be preserved.”

Although the species is clinging to survival, frog experts around the world are rooting for them.

“Archey's frogs hold one of the special places in my heart,” English-born Gibson says.

“They're one of New Zealand's unsung heroes. In my world, the world of a herpetologist, they are as well known as the kiwi in the bird world.

“Colleagues from around the world will talk to me about how the Archey's frogs are doing. They are a high profile frog despite keeping a low profile in real life.”

A once high-profile New Zealand species has almost slipped from memory. Powelliphanta augusta, or the Mount Augustus snail, snatched international headlines when it was first discovered in the mid-2000s. They became a symbol of the battle to protect nature from industrial extraction.

The molluscs were taken from Mount Augustus into captivity before their habitat was mined for coal. For the last 17 years, they’ve been lovingly cared for in fridges in a DoC facility in Hokitika.

“If you look at the history of those snails, the deliberate decision that was made effectively to make them extinct back in 2004, for the sake of jobs,” says Forest & Bird chief executive Kevin Hague.

“It's at the most extreme end of the problem. For the most part, we're oblivious to the consequences, a willful blindness. In this case, it's not blindness at all. We knew with clear, 2020 vision, this would be the consequence. We just decided that nature wasn't as important as the economic benefit.”

DoC science advisor Kath Walker discovered the snails. “It was a bit sad, because finding a new species is actually pretty neat. That in 2004, you could find something as interesting, and as beautiful [and] get to name it. That should have been fabulous but actually, it was heartbreaking.”

Over millions of years, the snails had evolved and slowly climbed their way up steep slopes to a tiny slice of the Stockton Plateau, high above the West Coast. There are two subspecies – the northern kind of which 6114 were rescued, and the rarer southern subspecies of which only 25 were found.

“When we found the snails there was only a tiny fragment of their habitat left,” Walker says. “It's a strange, remarkable place. It gets a heap of rain, six metres a year. It's like a little Japanese bonsai garden, everything's hiding from the wind and growing low to the ground.

“It’s a really harsh place to live. And yet, the snails have managed to conquer it.”

After almost two decades away, can they reconquer it and return home?

The site changed hands when state-owned Solid Energy collapsed in 2015, and is now mined by a Bathurst Resources and Talley’s joint venture.

“We have finished mining the ridge line just in the last year. And it has now been progressively rehabilitated,” says Stockton’s community and environment manager Barry Walker.

“It's a long, involved and committed process. This is really the exciting end of the project. We made sure the surface was stable, then brought in vegetation from other areas of the mine, a bit like laying a lawn.

“It brings with it the whole ecosystem, the way that it was before. The living organisms within the soil, the vegetation, the seed bank, all come with it. And the success of the vegetation transfer programme has just been tremendous.

“The vegetation is deemed acceptable for the release of snails, juvenile snails and the eggs. And that's exactly what's been happening over the last few years: a snail release programme.”

Walker says the mine and its employees are committed to returning the site back to nature.

“The snails are the butt of jokes. That you would spend so much time and money and effort for a snail,” he says.

“But, it's much more than that. It's a native species of New Zealand that we committed to look after. It's a real myth to think that miners drive a big digger and dig a big hole and spray and walk away.

“They care for this environment. They choose to live here because this is a beautiful place. And this is what they can do to ensure that it remains a beautiful place that they can be proud of.”

Kath Walker is not so optimistic. Just over 3913 of the northern subspecies were returned to the mine, in an area unfamiliar to them. Subsequent monitoring has shown no consistent evidence of a stable, or increasing population.

“They were surviving. I guess our concern has always been that it's a longer term thing. We didn't expect them to just die immediately. But the real problem is this changing environment,” she says.

“Mount Augustus was a cloud capture and every 100 metres in altitude that you gained, even more rain would fall. [Because] the top of the mountain was gone, these snails were [placed] some hundreds of metres below.”

Hot, dry summers, that are increasing in frequency, put the released snails in jeopardy, because they are prone to drying out.

“It's going to be a 30 or 50 year drought, that could wipe out the whole population,” Walker says.

“Because of that uncertainty, we kept about 1500 of the snails, including the 25 from the southern end, in captivity as an insurance policy.”

Hague believes they can never return to the home they once had. “I acknowledge there are some people who are putting a lot of effort into trying to recreate a habitat.

“But it's the very existence of minerals close to the surface, that unusual geology, that also means that the biodiversity associated with that place is also particularly special. You dig it up? The biodiversity is severely compromised, you may have lost it forever. In the case of those snails we probably have.”

There is another problem. The snails eat through a $60,000 a year DoC budget. So who will pay for the rehabilitation?

“Well, it's our job, isn't it?” says Kath Walker. “We, as a country, gained from the mining of the coal, it was a state-owned enterprise.

“We dislodged a whole species by doing this mining, and it's up to us to provide the funds to make this happen. It's going to be hard. But we haven't even tried because we haven't had the money to do the large-scale reconstruction of the environment that it needs.

“Time has moved on and, and the world's forgotten, and we still haven't got a pathway to try and fix it.

“I have invested so much of my life and I want to try and get us through this next bit of it, because it is achievable. We've just got to do it.”