A beating heart in our forests
Preserving what habitat remains will be crucial for our small flying mammals.
In one of my favourite Calvin and Hobbes cartoons, Calvin’s disregard for facts becomes evident to his whole school class. When he presents his report on bats, his description of bats as ‘‘unspeakable giant bugs’’ is greeted with a chorus of ‘‘Bats aren’t bugs!’’, before he is sent off to the principal’s office yet again.
Calvin’s classification of bats as insects rests on his view that bats fly and are hairy and ugly. Well, two out of three ain’t bad: bats do fly and, like all mammals, they have hair. Whether or not they are ugly is a matter of opinion, of course. I think they are pretty cute.
As every schoolchild in Aotearoa New Zealand learns, our country is almost devoid of native land mammals. We have plenty of native marine mammals, of course: whales, dolphins, fur seals and sea lions. And many mammals have been introduced, often for agriculture (cattle, sheep) but also for other reasons and many of the latter have become pests (rabbits, stoats,
A tiny (12g) longtailed bat from the Catlins.
possums). We have just two bat species that are native and terrestrial, although we had a third until the 1960s when it probably became extinct.
Our bats/pekapeka are tiny, weighing no more than 15g as adults. They are nocturnal and are now restricted to just a few parts of the country. Consequently, I suspect most people have never seen one.
Even if you specifically look for bats, they are not easy to find; today’s scientists often resort to socalled bat detectors, electronic devices that locate bats by eavesdropping on their high
frequency calls. These calls, usually too highly pitched for the human ear, are used to echolocate in the dark, enabling these flying animals to navigate through the bush and to find their insect food.
Both species hibernate during the colder months and give birth to one pup during summer.
Our two remaining bats are not closely related. Indeed, the lesser shorttailed bat has no close relatives anywhere in the world anymore. It is classified in its own endemic family, which diverged from some South American bats more than 40 million years ago. There are fossil relatives in the Australian Oligocene and
Miocene, but nothing more recent than about 12 million years ago.
The last known population of the closely related greater shorttailed bat, which was once widespread in New Zealand, was wiped out by the rats that invaded Taukihepa (Big South Cape Island) in 1963. This disastrous incursion also exterminated the bush wren/matuhituhi (related to the rifleman) and the Stewart Island snipe/tutukiwi.
Compared with other bats, shorttailed bats are unusual in spending much of their time on the ground. There they use their sense of smell to forage for a wide variety of foods: insects and other arthropods, small fruits, pollen and nectar. In their wanderings around the forest floor, they are important pollinators of several plants, including the endangered parasitic wood rose.
Our second bat species, the longtailed bat, has related species living in Australia. Even smaller than the shorttailed bat, it is an aerial predator, catching insects while flying. They can be seen at dusk in some parts of the Catlins, as well as in Oban on Stewart Island. The Eglinton Valley in Fiordland is particularly special in having both species.
Our bats, like our birds, are vulnerable to introduced predators. I have already mentioned rats, but cats are a problem, too. One feral cat was recorded as killing more than 100 shorttailed bats in just one week.
Perhaps even more than our birds, bats are fussy about their forest. They prefer extended areas of forest, with large, old trees in which they roost communally. Consequently, logging and other sources of forest damage, such as the new Mt Messenger bypass in
Taranaki, can cause longterm harm.
Preserving our only native terrestrial mammals is important, not just for their own sake, but also for the conservation of our plant taonga, such
as the wood rose.
Invasive radiata pine is spread more widely across Aotearoa New Zealand than was previously appreciated, and new modelling shows that up to 76% of the country’s land area is climatically capable of supporting populations of the trees. Radiata pine can invade a wide range of environments, and its fast growth means it may have strong effects on vulnerable ecosystems. More work is needed to better manage current invasions and prevent future invasions, and the authors recommend a levy on economic uses of invasive species to offset the cost of managing invasions. —