There are many people out there who do glass repairs. The bill will be a bit tricky, but someone with enough skill can pull it off. I would like to see how repairs are done. I'm too clumsy to ever try it myself, but it would be interesting to see how the professionals do it.
Another possibility is the buyer just wanted the good bird to add to their on damaged sculpture. I think the birds would look a bit awkward setting on the ground. There is a Cenedese bird with wings spread that has been offered on eBay. Normally it sets on a base, but this one sets on the ground. It looks like it fell from the sky and is laying, waiting for death. Very awkward.