They’re bats Jim, but not as we know them
New Zealand is a land of birds, reptiles and invertebrates due to separating from Gondwanaland 80 million years ago, or thereabouts but that doesn’t mean it’s mammal free. Aside from cetaceans (the whales and dolphins) and pinnipeds (seals and sea lions), microchiropterans (‘small’ bats) found their way to these remote islands. And like the other species to find themselves on Aotearoa these bats have been shapes by the unique forces of natural selection New Zealand has to offer. Two species remain the lesser short-tailed bat (Mystacina tuberculata) and the long-tailed bat (Chalinolobus tuberculata). The long-tailed bat, known as Pekapeka-tou-roa in Māori, is much your conventional small insectivorous bat. They live in colonies in the forest and hunt insects above, amongst and below the canopy. Their populations are monitored to assist in understanding the impact pest control is having on their numbers, as unfortunately they easily fall prey to the rats and mustelids introduced in New Zealand.
Once captured the bats are sexed, weighed, measured, aged and if a new capture, given a wing band. Sexing is easy, and aging is accomplished by looking at the amount of osteogenesis of the phalangial (finger) joins in the wing by shining a light from behind.
Once all the measurements are taken the animals are released and as the study is many years old and the populations are growing under the predator control operation, we can have confidence that the monitoring does not significantly hinder the bats.
Bats are fascinating creatures, and whenever I get the chance to watch them closely I find myself wondering how they perceive me. I see in light wavelengths that my brain interprets as colour and lightness. Together I interpret these images as the view reaching my eyes. But bats see in sound, chirping out high frequency calls and listening in detail to the echos that return. That but is simple enough but how does their brain see those images? Different colours for distance or texture. I’m sure the truth is more amazing than anything I can dream up. The world around us and these magnificent little products of evolution are proof that we really are in the infancy of our comprehension of life.
So the long tailed bats are fairly regular little guys as bats go, but their larger cousins, the lesser short-tailed bats are very different. These bats have well and truly taken the New Zealand lifestyle to heart. They haven’t lost the power of flight, as many of our birds have, but they have made adjustments to allow them to forage on the ground. These bats roll their wings up extremely tightly and have two rather than one thumb claw which they use to help them forage amongst the leaf-litter on the forest floor for invertebrates. And they’re voracious little chaps. Whereas the long tailed bats can be handled with impunity (and care), the short tailed bats merit a glove.
These bats are also extremely vulnerable to introduced predators and in need of seriously intensive conservation management. As part of this, as with the long tails, study populations are monitored for responses in their survival following pest management. However,being larger bats means these can be implanted with transponder chips.
But the unique characteristics of short-tailed bats don’t stop at foraging on the ground with ‘roll-up’ wings and two thumb claws. These bats sing. They sing just as song birds or frogs sing to advertise their prowess as individuals with mating with. Whilst many of their echo-locating calls are too high a frequency for us to hear these advertisement calls are easily audible to all but the older or rifle-shot ears. Using tree holes as sounding chambers these bats ca be located from their calls from 10s of meters away. It would seem there is stiff competition for good calling sites too. The bat photographed below went quiet when I shone my torch on him and almost immediately other bats tried to land and enter his calling spot, which immediately elicited a chase and tirade of ‘I’m still here’ calls.