Evolution: Why are there no flightless bats? We’re closing in on an answer

IN THE undergrowth of a New Zealand forest, something stirs. A small, fuzzy animal is scurrying over tree roots and through leaf litter, foraging for insects and fruit. It scuttles with an odd gait, as if on stilts. Is it a mouse? A bird? No, it’s a bat. The New Zealand lesser short-tailed bat, or pekapeka-tou-poto, to be precise.

Bats first took to the skies about 52 million years ago, and they have stayed there ever since. Among the world’s 1300 or so species, not one of them is flightless. Most can’t even walk very well, which is why many of us would be surprised by the behaviour of the pekapeka-tou-poto, a bat as comfortable on the ground as it is in the air.

But exactly why there are no flightless bats is an evolutionary mystery. The other great group of flying vertebrates, birds, have evolved to be flightless multiple times globally. They often do so on remote islands, such as those of New Zealand, where there is little danger from ground-based predation (at least until humans come along – roast dodo anyone?). In these circumstances, flightlessness is a good adaptation because flying is energetically costly.

As the world’s most terrestrial bat, the pekapeka-tou-poto has long seemed key to explaining the curious absence of flightless bats. But research over the past 20 years has revealed a surprise: many other species of bat can also walk. Some can even…