Townsend's Warbler x Black-throated Green Warbler

Townsend's Warbler x Black-throated Green Warbler hybrid, Crow Valley, Weld County (Colorado, USA), 2nd September 2015 - copyright Steve Mlodinow

(photo ID: 2283)

Best I let Steve explain this one...

"This bird's initial appearance is in the eye of the beholder.  Many will see Townsend's Warbler, as its cheek and crown are black and there is extensive yellow below the black throat.  However, the black throat expands laterally to join the side streaking, not as much as in Black-throated Green Warbler but more so than in Townsend's Warbler.  The auricular patch is narrower, particularly towards rear, than in Townsend's Warblerand the yellow crescent below the eye is larger.  The olive back was utterly unstressed, as in Black-throated Green Warbler but wrong for adult male Townsend's Warbler.  Interestingly, both adult male Townsend's Warbler and Black-throated Green Warbler have gray uppertail coverts and an olive rump that are streaked.  Finally, the undertail coverts are unstressed, a rare finding in Townsend's Warblerat any age, and particularly so in adult males."

Steve refers to a paper in the Journal of Avian Biology, "Hybridization between Townsend's Dendroica townsendi and black-throated green warblers D. virens in an avian suture zone" (Toews, Brelsford and Irwin, 2011) (Journal of Avian Biology 42: 434-446).  Steve tells us that the authors found that only 4 of the 137 birds scored to phenotype by were “intermediate” with most largely resembling one parent or the other.  And there's apparently more information on this hybrid in "Two recent records of apparent Black-throated Green Warbler x Townsend’s Warbler in Colorado" (Mlodinow, Walbek and Leatherman, 2014) published in Colorado Birds 48: 102-106.

Townsend's Warbler x Black-throated Green Warbler hybrid (same bird as in photo ID 2283 above), Crow Valley, Weld County (Colorado, USA), 2nd September 2015 - copyright Steve Mlodinow

(photo IDs: 2284-2286)

Townsend's Warbler Setophaga townsendi (formerly Dendroica townsendi)
Black-throated Green Warbler Setophaga virens (formerly Dendroica virens)

Townsend's Warbler x Hermit Warbler

Townsend's Warbler x Hermit Warbler hybrid, Sequim (Washington, USA), 28th October 2011 - copyright Steve Mlodinow

(photo ID: 1378)

Ageing this bird is important to its ID and in response to one suggestion that it might be a young female Townsend's Warbler (and not a hybrid), Steve explains that the moderately streaked back should make it an adult.  The dark cheek patch supports that idea and he goes on to say that it is reminiscent of Hermit Warbler.  It had a grey crown, nape, upper back and  wings plus what he describes as a most peculiar blend of grey, yellow, and white on the throat, all of which (when combined with the Townsend's-like cheek patch) point towards it being a Hermit x Townsend's hybrid. 


The yellow surrounding the auriculars (ear coverts) was a slightly different colour from that of the Townsend's Warbler with it - a bit more "lemony" or perhaps "less saturated" yellow than that of a Townsend's Warbler.

Townsend's Warbler x Hermit Warbler hybrid (with Townsend's Warbler on left in lower photo), Sequim (Washington, USA), 28th October 2011 - copyright Steve Mlodinow

(photo IDs: 1375-1377)

 

Townsend's Warbler Setophaga townsendi (formerly Dendroica townsendi)
Hermit Warbler Setophaga occidentalis (formerly Dendroica occidentalis)