The Blue-grey gnatcatcher (Polioptila caerulea, family Muscicapidae, subfamily Sylviinae) is a tiny, migratory, insectivorous songbird, the sole representative in Canada of the tropical New World tribe, Polioptilini (11 species). It is slender-bodied, blue-grey above, whitish below, with a long, black tail. Its song is high-pitched and squeaky; more commonly heard is a buzzy call note.

The blue-grey gnatcatcher is rare in Canada, breeding only in southern Ontario and Québec in open, broad-leaved deciduous woodland with brushy undergrowth. Nesting occurs late May to mid-July. Clutch includes 4-5 eggs.