This morning Ron Thorn found a Dusky Warbler at a seemingly totally random patch of fennel in South San Francisco (San Mateo County), a testament to how thoroughly he birds the county. Leonie Batkin quickly got the word out and provided directions, so I immediately abandoned my plans of checking shorebirds and running errands and went straight for the bird. Ron and Leonie were still there when I arrived, as well as a handful of other birders. The bird began calling in front of us almost immediately after I showed up, and miraculously hung out more or less in front of us for almost two hours despite a lot of usable habitat stretching toward the bay. Not that it was a confiding bird, but considering how skulky this species is, I thought it was fairly cooperative. I was decidedly unable to crush it (there was a lot of manual focusing involved), but here are some usable photos.
I don't know much about Phylloscopus warblers, but the bird seemed like a solid Dusky; no wingbars, long tail (it looked very "long" overall), short primary projection, very thin bill, and the call (which I heard dozens of times) was very similar to a Lincoln's Sparrow chip note and essentially was identical to the calls the 2015 Marin Dusky Warbler was giving.
The only unusual field mark to my (untrained) eye was the noticeably pink legs; they are "supposed" to have dark legs. One source says that 34% of all Dusky Warblers have all-pink or yellow legs however, so this feature would certainly fall within what is considered normal variation.
If you go for this bird, beware the Lincoln's Sparrows in the fennel patch, as their calls can lead you astray. I would also advise against barging straight into the patch, which I overheard a couple birders suggest today. The bird shows itself regularly and calls frequently, folks have photos, so there really is no reason to lurch around in there unless you are aiming to scare it away. Watch the bird from the edge of the patch on the top of the hill, or you can go the Michael Park route and try from the other side of the creek. Check Calbirds or pen-bird for directions.
The warbler had a habit of feeding low in the fennel, then working its way up the stalks and into view; once it got to a certain height, it would drop down and move over a few feet, then repeat. It was most often foraging alone, though sometimes a flock of Bushtits would overrun the area the bird was occupying.
According to Ron, this is the first San Mateo County record; I believe it would be the 11th record for California. Last year's Dusky at Redwood Creek was the only one I'd seen before, and trying to get a look at that bird was an absolutely heinous experience. Getting solid looks at this bird was no problem in comparison; we had better looks of this Siberian MEGA than we did of the Yellow Warblers and White-crowned Sparrows that were also around.
Isn't September great?