I have 2 bird boxes that have had sparrow nests in. One also contains a camera. I was surprised yesterday afternoon to see that the three babies had gone from the nest I was watching. Today I was gardening and under that nest box were the three half fledged babies, all dead but with no visible injuries. I buried them and swept up my hedge cuttings then suddenly found 3 more tiny babies under the other box. Again, no visible injuries but probably just hatched.
They have none of them been taken for food, none were hanging out of the nest box hole as they were all too young and were deep inside, none showed injuries. One box had a perch so I guess something could have stood on that but the other had no perch.
I cannot fathom what animal would plunder 2 nests within hours of each other, what animal could get in there, why it would only throw the babies out and, if the babies had died so the parents threw them out, what could kill 6 baby birds in one go?