Fruit bats diet in captivity

[Elephas Maximus]

Ewerywhere it is stated that fruit bats are frugivorous only.
However, in captivity they readily eat protein foods like yougurt.
The Egyptian fruit bats were observed hunting live prey.
I work in a butterfly house, where the bats are in free flight, and they're often seen catching butterflies, both in flight and while on the perch (if the butterfly lands near them). Only the body is being eaten.
Moreover, several times the bats killed and ate zebra finches & white-rumped munias (catching them sleeping at night). Usually most of the bird was left uneaten.
Does anybody have more info on fruit bats predation?

 

[Tunanta]

This is interesting. Are you sure it was the bats killing the zebra finches etc not just them fighting and killing each other or something like that? I'm a researcher, I study bats (UK though so no fruit bats) and it seems very strange for them to eat birds. I suppose it could also be the result of the artificial captive situation-any idea if it has happened in the wild? If it is the bats killing everything, they may be better off in their own enclosure!

 

[Elephas Maximus]

Yes, those were the bats. Finches won't rip away each other's heads!
And several people observed bats eating butterflies - even in daylight.
In addition, there's a large breeding colony of egyptian fruit bats in my city zoo (Ekaterinburg zoo). Several attempts of cannibalism were observed. If a weak baby falls off to the floor, it would probably be injured by conspecifics (probably not parents), that bite chunks of flesh off it.
Many of the bats often land on the floor searching leftover food (they're feeding at hanging dishes, many pieces fall down), and they regard fallen babies as food too.
The zoo's enclosure size is quite small (about 2 square meters for 60+ animals),
they don't spend much energy here.
In a butterfly garden, 100+ square meters for 4 specimens (but they're caged overnight now to prevent attacks)
The cause of such situations in captivity may be the need for protein when plant diet doesn't provide much of it (even bananas). The bats are probably hunting butterflies in the wild too, but it's hard to observe. After all, among fruit bats only Rousettus genus has a sonar, and may use it for hunting like Microchiroptera.
The prey's size is all that matters for attack decision. Sleeping bird is relatively small, and even if awake, the wingspan is about 1/4 of bat's.
Birds were never eaten completely, just the heads and upper body.