Black-throated Blue Warbler on the wintering grounds

Last week I assisted Roselvy and Lya with bird banding in Montecristo national park, in El Salvador, where we caught this female Black-throated Blue Warbler, a bird that normally winters in the Greater Antilles - Puerto Rico, Cuba and Jamaica primarily. Black-throated Blue Warblers don't leave the wintering grounds until late March to April (Holmes et al. 2005), so this bird likely spent the winter in Montecristo. This is one of the few warbler species that appears to be increasing, as fields and pastures in the heart of its breeding range (northeastern US) have been returned to forest (Holmes et al. 2005). In striking contrast, this species is likely encountering severe habitat degradation on its wintering grounds.

Regular readers may remember that I encountered this species also in Chiapas, Mexico: I saw two individuals in December 2008. And last week's capture was not the first time for this species to be recorded in Montecristo either, for there are single records from 2004 and 2006. It has also been caught twice in the last seven years at another SalvaNATURA banding station in El Salvador, at Los Andes (in Los Volcanes national park). Holmes et al. do not mention records from Pacific Slope Central America, they only mention that the bird is "occasional along the Caribbean coast of the Yucatan, Belize, Honduras (...) and a rare or casual winter visitor along the Caribbean coasts of Costa Rica, Panama, Colombia and Venezuela" (Holmes et al. 2005).

I realize at this point it is pure speculation on the basis of a few incidental sightings, yet I can't help but wonder if healthy breeding populations of Black-throated Blue Warbler faced with habitat destruction on the wintering grounds are looking outside their 'normal' winter range for alternatives?


Cited literature
Holmes, Richard T., N. L. Rodenhouse and T. S. Sillett. 2005. Black-throated Blue Warbler (Dendroica caerulescens ), The Birds of North America Online (A. Poole, Ed.). Ithaca: Cornell Lab of Ornithology; Retrieved from the Birds of North America Online: http://bna.birds.cornell.edu/bna/species/087