stevil
Godless and without morals
Well, not all birds in NZ became flightless, so I guess there was an advantage for some species to fly.How come bats did not evolve into something else? No mammalian predators to attack them either.
But it is a good inquisitive question.
Here is an article I just found on google about that topic

Why are there no flightless bats? We're closing in on an answer
A careful look at the few bats that can walk on the ground – including the common vampire bat – is helping us understand why evolution has yet to produce a flightless bat
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.
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