[All photographs copyright, Gary Nunn 2012] – I almost went early this morning to Lower Otay Lake, Chula Vista, to look for the Blackpoll Warbler reported yesterday, but decided to go birding later once the temperature warmed up. As several very experienced California birders pointed out, this is a very unusual winter date for a Blackpoll Warbler and worth investigating. So when word came out that the identification had been revised to a much rarer Bay-breasted Warbler, along with the discovery of a Prairie Warbler no less, I jumped in the car and headed down to the lake! By the sound of things a posse of local birders had been picking over the rare warbler finds!
This adult male Praire Warbler was discovered by local birder BJ Stacy in the small willows along the edge of Lower Otay Lake just on the north side of the boat ramp. It was very mobile while I watched it move among willow trees dotted along several hundred yards of shoreline both north and south of the boat ramp. It even flew out to the submerged willow islands near the end of the jetty at one point! It did occasionally come very close and, since it was feeding low in the bushes, provided excellent photographic opportunities.
Originally reported on 30 Dec 2012 as a Blackpoll Warbler, this bird is perhaps the most difficult identification challenge among the Parulidae Wood-Warblers. The next day local birders Jay Keller and BJ Stacy relocated the warbler, joined later by Paul Lehman and Guy McCaskie, and revised its identification as a much rarer Bay-breasted Warbler! There are several key diagnostic features that contribute to its identification including most importantly the evenly blue-grey colored legs and feet (including soles of the feet) which can be seen in the photographs below. I also think the undertail coverts have a slight buffy coloration, at least at the sides where they meet the flanks, which is another feature of Bay-breasted Warbler. Looking at details of the plumage from the photographs this appears to be an adult female. Only the outer two rectrices have white markings, and the white mark on r5 is small. In addition the rump has a noticeable lead grey coloration that contrasts with the yellowish-green upperparts.