Interesting! Must be the fruit-eating varieties you're talking about? When I worked in the aforementioned Bat Lab (yes, it was fun to answer the Bat Phone!), we had a visit from a lab in Australia, where they were studying the physiology of the very large fruit bats they have there. That's a lot of weight on those wings, and without a lot of the adaptations that make it work for birds...And
these guys are big!
A couple of interesting things I remember from what they said about them thar fruit bats:
1. They had several that they worked with in their lab (they did similar high-speed filming of them, to see the wings flexing in super slow-mo), and they said they were super nice and
also liked being petted and cuddled.
2. They had wondered how the heck these rather heavy animals were able to hang from their toes, upside down all day while they slept. There's no way they could do it using muscles. So...You know how you have your carpal ligament, that runs through the carpal tunnel (you get "carpal tunnel syndrome" when the two rub too much, and get inflamed)? Turns out, on the bat version, they have ridges on both the ligament, and the tunnel. They're able to pull that ligament tight, and when they relax it, the "teeth" lock together-- kind of like the way you cinch a belt-- and their toes are held bent and locked tight around the branch, while their muscles can just relax. When they want to release the branch, just like you do with a belt, they use their muscles to tighten a little bit to unlock the teeth and let everything slide free again, and then they can let go. Isn't that cool?
Apologies to all for the thread highjack and random natural history lesson! ; )