This is one of the worst photos I have seen of a bird killed by a House Sparrow (HOSP). The Tree Swallow (TRES) head is not completely missing, but it is defeathered, with the skull exposed and the brain pecked out. A red-banded male HOSP was seen on and in the nestbox where this TRES was killed.
These photos were taken on an experimental trail where HOSP eggs and/or nests are being removed on a weekly basis, but HOSP are not being trapped but are being banded. Four Tree Swallows were attacked a month after the experiment began. Of those; three died (photo below) and one was taken to a wildlife rehabilitator. (Note: All of these boxes are mounted on poles with raccoon baffles.)
HOSP kills occurred in three separate boxes. In addition to the bird pictured at the top, two TRES were attacked in one box (seen in the photo below). The male died, the female was badly injured. She was taken to a wildlife rehabber but died the next day. A pair of banded HOSP were seen in the vicinity; that HOSP pair had a nest with two HOSP eggs in it which was removed 7 days prior to the attack on the TRES.
– Bob Orthwien