Status Rare transient, very rare in summer. It was first recorded at Norwood, Yarmouth County, where Allen (1916) collected one on 9 July 1904. It was not reported again until 1956, when Robert Gray saw a bird in Colchester County on 26 May. Since then, records of this bird have come from sources from Cape Breton Highlands National Park to Cape Forchu and the Lurcher Lightship off Yarmouth, and from all regions in between. About 22 birds have occurred in spring, between 15 May and 18 June. Over 70 have been fall migrants, from 15 August to 15 November, many of them on Brier and Seal islands, especially in September. Summer records are a bird on 9 July 1963 at North Aspy River, Victoria County (A.J. Erskine): another on 21-22 July 1980 at Wine Harbour, Guysborough County (H. Munro) and, most unusual, a singing male in Yarmouth on 12 July 1960 (C.R.K. Allen).
Description Length: 11.5-13 cm. Adults: Top of head gray or olive-gray, with a white line over and a dusky brown line through the eye; back, wings and tail gray-brown with olive tinge; underparts pale yellow, usually white on throat and belly.
Range Breeds from central British Columbia to central Quebec and southwestern Newfoundland, south to southern Alberta, northern Minnesota, New Brunswick and central Maine. Winters south of central Mexico.
Remarks The Philadelphia Vireo can be mistaken for a greenish warbler, particularly the Tennessee Warbler. However, it has a thicker bill and is more sluggish than any similar warbler. Its yellowish underparts and unbarred wings are marks which distinguish it from other vireos known to occur in Nova Scotia. It breeds in New Brunswick, may breed here and probably occurs with greater frequency than our records indicate.
The species was first described in the early nineteenth century from a bird which was collected incidentally in Philadelphia, hence its name.