Monday, November 16, 2009

Black-throated Green Warbler

Today a picture of a Black-throated Green Warbler, taken last week in Parque Natura in Xalapa, where this species is an abundant winter resident. This bird is an adult male, as evidenced by the entirely black throat and breast, heavily veiled with thin white tips. The thin white feather tips are part of the fresh fall plumage of adult males, and wear off in the course of the winter, when the entire throat and breast turn a solid black. The bill, here with some brown along the gape, will also turn completely black during winter. Immatures show more brown on the bill.

This species is of course far more common than its sister species, the Golden-cheeked Warbler, which I will be looking for in Central America once again this winter. My field crew will be visiting Honduras and Costa Rica in search of them. Costa Rica is really outside the known wintering range for this species, yet records exist for that country. We will attempt to describe 25 mixed warbler flocks in Costa Rica, in hopes of encountering maybe a few goldencheeks if we're lucky. We will be seeing far more Black-throated Green Warblers, a common winter resident there also. The adult males of both species are distinctive and easily separated. At the other end of the plumage spectrum, immatures of these two species - especially immature females - are quite similar. When given good views, even these plumages are separable in the field, for the upperside of even the drabbest goldencheek will still be darker than that of any black-throated green, while the auricular patch on the latter species is never present on a goldencheek. The eye line of goldencheeks is always more pronounced than on black-throated greens. The vent of any goldencheek is pure white, while black-throated green always shows a yellow wash in that area, fainter in some individuals. With care, they can be separated.

It's possible that some Costa Rican records of Golden-cheeked Warbler pertain to misidentified Black-throated Green Warblers, and it's also possible that goldencheeks do winter in very small numbers in that country. I know we will be searching for a needle in a haystack, but that should make it all the more rewarding if we do find one, or some.

My visit to Parque Natura was not to look for Black-throated Green Warblers, but for the endemic Hooded Yellowthroat, said to occur there in open, brushy situations. Bob Straub's bird finding guide to Veracruz states that the species is more easily found there in spring and summer, when the males advertise territories. Still, I thought I'd give it a try, after having dipped on the Burrowing Owls the week before. This was another species I had never seen before. After many hours of searching I did eventually find a female, which came out of the brush briefly upon spishing, long enough for satisfying looks but not long enough for an actual photo. It was accompanied by a Wilson's Warbler, which was more cooperative.

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