Yellow-green Vireo
Fort Funston
San Francisco, California
30 September 1998

Today I decided to check the grove of trees on the west side of Skyline Drive at Fort Funston in search of a Yellow-green Vireo and a Black-throated Green Warbler reported earlier today by Brian Fitch. When I arrived I found John Luther, Mark Eaton and Josiah Clarke already there. Soon I saw a Blackpoll Warbler and the Blackburnian Warbler I had discovered there on Monday was still present. Later we enjoyed close views of a Clay-colored Sparrow and a male Black-throated Blue Warbler.

But it wasn't until about 4:30pm when Josiah found the Yellow-green Vireo and another 15 or so minutes before everybody got good views. At this time Calvin Lou and David Nelson arrived and helped keep the vireo under observation. I first saw the bird preening fairly high in the cypresses, but then the flock of warblers and chickadees moved to the south and finally we got great views in the Albizzia shrubs just south of the grove.

It was a large vireo about the size and shape of a Red-eyed Vireo, but was immediately distinguishable by its bright yellow-green upperparts. The crown was gray and the dark eye was marked by a rather narrow indistinct pale supercilium. The supercilium was bordered above by a blurry dark gray blending into the gray of the crown. This gray color contrasted strongly with the yellow-green back which extended up onto the nape. The bill was quite long, fairly thick and decidedly pale in color with only the hook at the tip being dark. The underparts were mostly whitish, with a pale yellow wash extending from the ear coverts across the side of the neck and down the breast and sides to the flanks and undertail coverts. This yellow had a decided greenish cast to it so it did not appear to contrast much with the upperparts. The undertail coverts were considerably brighter yellow than the rest of the underparts and were particularly visible because of the bird's habit of holding its tail cocked in the air with its wings drooped. The legs and feet were blue gray.

At one point the bird switched position back and forth repeatedly on a branch as though it were some sort of mechanical toy, a very interesting behavior. It also craned its neck from time to time and seemed to peer around a lot.

I looked for yellow-green edges to the wing-coverts, and although there was certainly an impression of feather edging, the bird was not close enough to detect fine detail. There was no evidence of wing-bars. The upperside of the tail was yellow-green, same color as the rump and back, but the underside of the tail was gray, evident when the tail was cocked in the air.

David Nelson attempted photos, but I'll be surprised if they come out.

Joseph Morlan
380 Talbot Avenue #206
Pacifica, CA 94044