They could not be seen well enough to be sure. Burrows and Caves of Africa is attached to this building and I think these are excess Egyptian Fruit Bats from there.
Now that the weather is going downhill I will be inside more to catch up to a keeper for confirmation.
I have changed the title. Later today I will try to find out why they are in that location.
Incidentally, although I am not much interested in bats, the Burrows and Caves area has the most interesting and engaging information displays of the whole zoo. It is the only place I have seen people, on a busy day, waiting to get a look at everything.
That is true, it is surprisingly busy for such a small section of the zoo. I usually walk right passed it without even thinking of going in. Can never get a decent shoot on the animals in there.
And just to clarify Mr. Wrinkly, this is in the large cage inaccessible to visitors getting up close, right? Where the other Hamerknop is located?