All creatures great, small and vanishing
We can’t see them, and they give us the heebie jeebies. But some of our most invisible endangered species are indicators of the health of our natural environment. Andrea Vance and Iain McGregor report.
Bats get a bad rap. Associated with eccentricity or absentmindedness: ‘‘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 bat, but the greater short-tailed is probably extinct. The lesser short-tailed is found only at a few scattered sites.
‘‘The short-tail bats are important pollinators and seed dispersers,’’ says Colin O’Donnell, principal science adviser for the Department of Conservation (DOC). ‘‘They eat nectar and certain flowers and pollinate them.
‘‘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 longtailed bat is classed as ‘‘nationally critical’’, and the short-tailed subspecies range from ‘‘nationally vulnerable’’ to ‘‘recovering’’.
But the mousy-grey shorttailed 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. 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.
‘‘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.’’
By 2000, numbers were getting 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.’’
Catching bats to study them isn’t easy. Because they use echolocation, conventional nets for trapping birds are useless.
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 highfrequency speaker, emitting bat calls, to lure the animals, which are deeply social. Once caught in the plastic liner, the bats cuddle together until they are handled by researchers.
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