Black-throated Grey Warbler

Probably the most uncommon of the common warblers we see in Sonoma County. Present during the summer months, but probably most often noted during spring and autumn migration, especially the latter. Mid- to late September to early October seems to be the best season to see this bird in the county. Rare here in the winter. Breeds in dry, interior habitats as far east as Colorado and Arizona but also coastally as far north as mid-latitude British Columbia. Breeds in Sonoma County, but confined to the interior of the county and upland ridges, according to Burridge. Winters in Mexico and South America. Often solitary, but may be seen in loosely associated mixed flocks during migration gleaning insects. Occasionally flycatches or hover-gleans. Comparatively tolerant of close approach, as warblers go.

Perhaps the most distinctively plumaged of our fairly common warblers. Striking head pattern: black crown, white face with black cheek, white malar stripe, and then black again at the throat in the adult male. Females often lack the black at the throat or show irregular, patchy black there. Females usually greyer overall. The bird pictured above is probably a first fall female or young male. Grey back, two white wing bars, white underneath but with streaky flanks, white under the tail. Young birds may be slightly buffy underneath. Yellow supraloral spot clinches the identification. Spot may be paler in juveniles and females, but always present. Outer tail feathers flash white in flight.

While Black-and-white Warbler (Mniotilta varia) is superficially similar, that bird gives the impression of being striped all over ("Zebra Warbler" would have been a good name; it has a white stripe through the black crown and a striped back, both features lacking in Black-throated Grey Warbler). Black-and-white Warbler also behaves rather differently, preferring wooded areas and sticking mostly to tree trunks where it suggests a nuthatch, and it shares something of the plump but tapered nuthatch shape. Also, Black-and-white Warbler is a far less common bird in Sonoma County, noted only a few times a year here during migration. Facial pattern may suggest a chickadee, but our Chestnut-backed Chickadees (Poecile rufescens) have a distinctive chestnut brown back and chestnut-washed flanks.

Buzzy song during breeding season is usually described as something like weezy, weezy, weezy, wheet. Peterson gives it as zeedle zeedle zeedle zeet che, saying that the last note or next-to-last note is often pitched higher. Noted for singing all day long during breeding season, persisting after other birds have settled down in the afternoon.

Selected county sightings: Spring Lake (September 15, 2012, Ruth Rudesill); Strawberry School Park (September 24, 2010, Colin Talcroft); Lake Ralphine (September 1, 2009, Colin Talcroft).