http://www.sialis.org/hosp.htm#theproblem
House sparrows kill bluebirds. The nestlings and, if the opportunity arises, the adult bluebirds too.
Ohhh I know. I have killed many a HOSP. Birds from hell.
The cats never seem to catch the damned house sparrows! Always warblers. The hiuse sparrows have killed many of my bluebirds and tree swallowss.