Blue-winged Warbler

Admittedly you probably can't see blue wings here, but this is apparently a Blue-winged Warbler, or at least that's what the iNaturalist folks tell me. Unfortunately this bird was a little too far away for me to point out most of the field marks:

• You can see that this bird is mostly yellow outside the wings, and you can probably tell that there's a black line going through the eyes. After that, you may need to use a little imagination.
• The wings are usually described as either "steel blue" or "blue gray"; I'm not sure you can conclusively call these wings anything more than dark, possibly earth-toned.
• They're also supposed to have 2 wingbars, which are from 2 rows of feathers (coverts) on the wings. I think I can see 1 wingbar in this picture. The other wingbar is presumably there but just isn't showing up in this picture.

Blue-winged Warblers are apparently close relatives of the Golden-winged Warblers, and the 2 species hybridize so often that their hybrids have their own names: Brewster's Warbler and Lawrence's Warbler [1]. Currently Blue-winged Warblers and Golden-winged Warblers are considered separate species, mostly because they look different, sing different, and generally live in different areas. Genetically though, a case could be made for them being the same species [2].

Brewster's and Lawrence's Warblers might have separate names, but they aren't considered species, getting the hybrid tag instead. For reasons that I'm assuming are historical, the distinction is that a 1st generation hybrid is a Brewster's Warbler but future generation hybrids are Lawrence's Warblers. 

Here's yet another hybrid factoid. There was a 3-species hybrid discovered, basically a Brewster's Warbler crossed with a Chestnut-sided Warbler. This was surprising because the Chestnut-sided Warbler isn't considered to be very closely related to the Blue-winged and Golden-winged Warblers, and thus also not closely related to the Brewster's and Lawrence's Warblers. There are quite a few instances of species in the same genus hybridizing, but hybridizing outside their genus is pretty unusual [3].

May 18, 2023 at Fairview Farm
Photo 292810665, (c) jpviolette, some rights reserved (CC BY-NC)

[1] Given the American Ornithological Society's name-changing plans, I'd expect Brewster's and Lawrence's Warblers to have different names down the line.

[2] This is another example where we may not have drawn the species line exactly where we should have.

[3] This is an example suggesting we may not even be drawing the lines between genera as well as we could.