Warbler song in migration

Black-throated Green Warbler

According to the Peterson Field Guide to the Warblers of North America, "male warblers sing almost incessantly early in the breeding season, and often in spring migration as well (especially as the breeding grounds are approached); many species begin singing before departing the wintering grounds." (Dunn & Garrett 1997).

This week I heard some migrant warbler song here and there among the rich chorus of resident species now singing down here in Honduras. A couple of days ago I obtained a poor recording of a singing Black-throated Green Warbler, while today I got a rather better recording of a singing Wilson's Warbler. Although the phenomenon is evidently not unknown, it remains poorly represented in bio-acoustic libraries such as Xeno Canto or Cornell's Macaulay Library. 

Unfortunately, the Black-throated Green Warbler is barely audible as its weak song is drowned out by a chorus of cicadas. Listen carefully for what I believe is a so-called 'unaccented song'. This Black-throated Green Warbler was in the company of at least three conspecifics, as well as two Blue-headed Vireos, a Black-and-White Warbler and a Magnolia Warbler. They were foraging in encino (thin-leaved) oaks on a sunny, south-facing slope at an elevation of about 1300 m.

This Wilson's Warbler was foraging in similar habitat, but did not appear to be associated with other insectivorous birds. The weak ending of his song suggests the nominate eastern subspecies. At the time of writing, Xeno Canto does not have any other Wilson's Warbler song from Central America, but the Macaulay Library has an excellent cut from Costa Rica.

Cited literature:

Dunn, J & K. Garrett. 1997. A field guide to the warblers of North America. Peterson Field Guide Series 49. Houghton Mifflin, New York.