Bat harems

Repost
These are short nosed fruit bats (Cynopterus sphinx). I like this picture and a lot of folks do as well. One of the reasons is I guess the nice geometric formation. But the other almost certainly is our human preference for large-eyed infantile creatures. These are nocturnal bats and cant echolocate so they use their eyes to find food and hence must have large eyes. Unlike the eyes of the next guy who is an insectivorus bat, which echolocates and creates a world view using that sense instead. Thats most probably one of the leaf nosed bat species (probably Hipposideros ater), and was shot in Lepakshi, AP. (Not pipistrel like I'd said before).

The other interesting thing about this group is that its a group. Most bats actually live in some kind of group. But this one is special, because its a harem. A male bat creates a resource, in this case its a roost. Actually under more natural conditions these bats build what are called tents. However this group lives in the eaves of the physics dept. And the females basically live in his resource and he gets the first go at reproducing with them. The groups remain stable over quite some time apparently, with some dynamic fusion fission going on. So I guess a female could truly 'evaluate' a male over a period. According to one study, harem keeping males though sire abt 65% of the offspring of harem females, not all interestingly!

A bat guy who came to the lab recently speculated that the guy outside the group is the male, he says that the male is probably the bat on the outside cause they dont usually stay within the group and are the first to leave at disturbance. Which are both interesting actually. Cause if you look closely at the image (click for a larger version) you'll notice ticks on some of the animals. All animals in groups face some costs, here females are sole parental care providers so there is no 'division' of the males efforts. But they will almost definitely get parasites from their roost mates. Also a big group is also always more attractive to a predator! (If you look carefully one of the bats has an eye missing, put out by a predator?)

Its interesting that males show behaviours that suggest avoidance of both these costs but the females don't! I wonder if and why the costs are assymetric between the sexes?