390-411 (general notes on warbler ID), pp. Kaufman, Field Guide to Advanced Birding, 2011, pp. 229-232 (general notes on warbler ID), pp. Kaufman, Field Guide to Birds of North America, 2000, p. 646įix and Bezener, Birds of Northern California, 2000, p. 66-67)Įhrlich, Dobkin, and Wheye, The Birder's Handbook, paperback edition, 1988, p. 434ĭunn and Garrett, Warblers: Peterson Field Guides, 1st ed., 1997, pp.
462ĭunn and Alderfer, eds., National Geographic Field Guide to the Birds of North America, 6th ed., 2011, p. 147ĭunn and Alderfer, eds., National Geographic Field Guide to the Birds of North America, 5th ed., 2006, p. 384īurridge, ed., Sonoma County Breeding Bird Atlas, 1995, p. 126īrinkley, National Wildlife Federation Field Guide to Birds of North America, 2007, p. These birds are now assigned to the genus Setophaga, but many older references will be around for a while, so expect to see this bird as Dendroica coronata, with newer sources using Setophaga coronata.īolander and Parmeter, Birds of Sonoma County California, rev. Note that as of July 2011, the genus Dendroica disappeared. For more, I recommend the Peterson specialty guide on warblers or The Warbler Guide. A picture is worth many words (see below). In the photo above, note the supercilium and the paler throat color that turns up behind the comparatively rich, brown ear patch-both indicating Myrtle Warbler.
In these plumages that cause confusion because of throat color, two features are useful Myrtle Warbler will always have a supercilium (or "eyebrow") or at least a hint of one, and the shapes of the edges of the white throat patch are different in the two forms, with Myrtle Warbler showing the white wrapping up and slightly around the back of the auricular feathers (the ear patch). As a general rule, forms with a white throat are Myrtle Warbler (as a mnemonic, think of W for "white" being an upside-down M for "Myrtle"), while those with a yellow throat are Audubon's Warbler-but that's an oversimplification while distinctly yellow-throated birds will always be of the Audubon's form, female Audubon's Warblers in their first fall and first spring will often have a whitish or a creamy throat. Nearly all guide books show the two forms of Yellow-rumped Warbler separately, and it would not be terribly surprising if they were at some point split again into distinct species. Both forms have a yellow rump (although, to complicate matters, the juvenile Myrtle form lacks the yellow rump patch), but the rump is not always the most conspicuous field mark, and, in most plumages, the two forms look quite different. Is this one species or two? Yellow-rumped Warbler was the result of the lumping of forms formerly known as "Myrtle Warbler" and "Audubon's Warbler" in 1973 (according to Kaufmann, they were lumped because the two species were known to interbreed in a zone in southwestern Alberta, Canada).
Most full adult plumages of both forms also have a yellow patch on the crown. Despite the bird's name, the yellow throat and flank patches of the Audubon's Warbler form are often much more conspicuous than the yellow rump patch. Usually solitary or in small groups, but, while staging to depart in the spring, may form flocks of 50 birds or more. According to Birds of Sonoma County, the Audubon's Warbler form (see below) greatly outnumbers the Myrtle Warbler form during migration and in winter. Least common in the county in June, July, and August. Numbers begin to thin again in mid-April through early May. The migrant population starts to arrive in mid- to late September. Yellow-rumped Warblers are present year-round in the county, but their numbers increase dramatically in the winter months. By far the most common warbler in Sonoma County from late autumn through late spring.