There has never been a summer that these boxes haven’t been occupied by someone ... The only hitch is that bluebirds remain somewhat vulnerable to two invasive species: the house sparrow and the ...

There has never been a summer that these boxes haven’t been occupied by ... only hitch is that bluebirds remain somewhat vulnerable to two invasive species: the house sparrow and the European ...

Though house ... sparrows (Spizella passerina), they aren't closely related. These invasive and aggressive birds can spell ...