There are probably close to 30 North American migrant warbler species that you can expect to encounter regularly in Costa Rica. Many of these have featured in earlier posts on this blog, but this year several notable species have been zipping around local hotspots.

The Golden-winged Warbler (Vermivora chrysoptera) is considered a species held to be a ‘conservation priority’ in the United States, yet it can be found fairly commonly here locally during migration season. Here are two different views of what was probably the first individual I ever saw:

Here’s a frontal view of the same male:

The genus Vermivora (literally ‘worm-devouring’) is now recognized to consist of just 3 species, one of which, Bachman’s Warbler (Vermivora bachmanii) is now, unfortunately, extinct. The third species, Vermivora cyanoptera, is the Blue-winged Warbler, considered a rather rare visitor to Costa Rica. One turned up at Aquiares this October, but in typical warbler fashion it moved constantly and was not easy to photograph:

It was The dark eye-line, white wing bars and overall yellow plumage clinch the identification. Warblers are notoriously difficult both to identify and to photograph. This year several uncommon species, such as the Hooded Warbler (a female) and the Worm-eating Warbler have also appeared at Aquiares. The following shots help to confirm the rare Blue-winged Warbler, a species which I myself have never encountered in all these years in Costa Rica:

The last shot, below, still shows enough of the white wing bars and precludes any possible confusion with, say, Yellow Warbler or Wilson’s Warbler, both of which are common migrants here.

Garrigues and Dean’s field guide The Birds of Costa Rica notes that chrysoptera and cyanoptera frequently hybridize. Two common hybrid forms are illustrated and named respectively Brewster’s Warbler and Lawrence’s Warbler. However, this situation is quite complex. The plumage of some hybrids can vary considerably and leave the average birdwatcher (that’s me) in great doubt as to precise identification. Local guide Steven Aguilar located the Golden-winged/Blue-winged individual that appeared in late October this year at Angostura:

At first glance most observers might think of a female Golden-winged Warbler, yet the shoulder patch more likely indicates a male. But then again the underparts are neither white as in a Golden-winged Warbler, nor the bright yellow of a Blue-winged Warbler. Steven was unfazed and identified it on the spot as a Lawrence’s Warbler hybrid, despite the lack of black throat patch and cheek. His identification proved correct of course, so I can now complete this post by adding a final photo. This shows the warbler’s head and underparts in the fairly dim light of the understory. My caption now reflects the identification currently assigned in the eBird database:

Lawrence’s Warbler (hybrid) Vermivora chrysoptera x cyanoptera (F2 backcross); photo by John Beer

See my next block for more migrating warblers in our part of Costa Rica.