Oregon

Birdwatchers were mystified by the near-total collapse of the subspecies of Wilson’s Warblers that breeds in California, Oregon and Washington. However, when bird banders joined an unlikely team of scientists, the ecological smoking gun emerged from chemical birth certificate signatures in the chryseola subspecies’ feathers as if by magic. This “breakthrough type of analysis” can now be applied to any unexplained decline of a subspecies or subpopulation of any migratory bird species.

Read more about this conservation science breakthrough in Rex Graham’s article titled Wilson’s Warbler Mystery Solved by Avian Detectives.

Editor’s note:

We often assume that familiar, widespread common species do not merit the same level of attention as scarce or localized species, and as a result birders often don’t give those common species a second glance. As this recent article on Wilson’s Warblers demonstrates, that assumption can lead to a false sense of security, and it is worthwhile for birders to take that second look, even for common species. The two subspecies of Wilson’s Warblers that breed in the Northwest, the coastal chryseola which is the subject of the article and the interior pileolata, have two very different conservation status.

Separation in the field is not simple, but is possible with some individuals, so eBirders can help monitor the status of both by taking a second look at the Wilson’s Warblers they encounter and identifying them to subspecies, if and when possible. As with all identification challenges, the most important rule is to use the subspecies designation only when the identification is certain, and carefully document any out-of-season or out-of-range identifications.

Coastal chryseola are brighter colored than pileolata, with many males showing a touch of orange on the forehead in front of the black cap, and all chryseola show bright yellow foreheads and lores. Most females, and even first fall birds, show some black on the crown. Chryseola are probably uncommon or even rare in the interior, as their breeding range is limited to coastal areas from central B.C. to southern CA and their migration is primarily north-south.

Interior pileolata, somewhat duller colored than chryseola, also tend to have less black in the crown and most first fall females show no black. Since pileolata breed widely across Alaska and northern BC, they are likely migrants through both coastal and interior areas, so identification by range during migration is problematic.

–Bill Tweit