David Sibley

An apparent Timberline Brewer’s Sparrow in sagebrush habitat

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Summary – A bird in sagebrush habitat showing features of Timberline (taverneri) Brewer’s Sparrow provides an opportunity to review the distinguishing features, and raises questions about range, variation, and taxonomic status. Comparing two subspecies of Brewer’s Sparrow Spizella breweri S. b. breweri often called Sagebrush Brewer’s Sparrow S. b. taverneri known as Timberline Sparrow On […]

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Male and female Eastern Kingbirds have different head shapes

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Detailing my new discovery that male and female Eastern Kingbirds are reliably distinguished by head shape – with the male having a more triangular head. This was verified across multiple birds in Montana, but needs further testing and might only work on adults. On a recent trip to Montana (June 2026) a pair of Eastern

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Identifying Mangrove and Northern Yellow Warblers in Florida and the Caribbean

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Following up on my earlier post about structural differences, here is a discussion about plumage differences between Mangrove and Northern Yellow Warblers. This post focuses on the two populations that are expected in Florida and the Caribbean – Mangrove Yellow Warbler (Greater Antillean group) and Northern Yellow Warbler (Eastern group). Other populations of both species

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The two species of Yellow Warbler differ in structure

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The split of Yellow Warbler into two species in 2025 (by Avilist) brings a challenging identification issue into the mainstream. It is possible to identify most by plumage color (more details here), but differences in the shape of body, wings, and bill provide more consistent clues for identification. Northern undertail coverts longer and fuller, which

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Identification of Eastern and Western Warbling Vireos

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Summary: In practice virtually all will be identified presumptively by range. Positive identification depends on careful analysis of details of song (but questions remain about variation in song). Positive identification of silent birds is not possible on current knowledge. The Warbling Vireos were considered a single continent-wide species until 2025, when two species – Eastern

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Distinguishing Philadelphia and Red-eyed Vireos by song: Is it possible?

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Possible? It might be, but most of the widely published “differences” are too subjective and/or too variable to be of any value. I dug into this a couple of years ago and discovered some details that seem more reliable, which are summarized in the one page file here (also as a pdf via this link:

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