This is the second year I have had swallows flying in and out of my very large shed. They were late lestng last year, the chicks hatched but sadly didn't survive. This year a pair came and added to the nest (this was about 5/6 weeks ago) although hey have been very busy flying in and out there doesn't seem to be any chicks yet. This morning I noticed 3 birds flying in and out, is this usual behaviour?