Yellow-throated Vireo (Vireo flavifrons)
Butterbredt Spring, Kern County, California
29-30 May 2004
Joseph Morlan

Robbie Fischer and I visited Butterbredt Spring to search for migrants and we were not disappointed. When we arrived about 8am, on Saturday 29 May, there were many Swainson's Thrushes and Western Flycatchers in evidence. There were also many other birders present who had located Northern Parula, American Redstart and Rose-breasted Grosbeak. However, none of those species were in much evidence when we arrive. Skies were clear and there was a moderate breeze. Most of the birders were in the sheltered area at bottom of the main grove of Cottonwoods. A call went out about the grosbeak and some of us rushed over to where the calls originated, but there was no bird by the time we arrived. I headed back to the sheltered area when somebody told me that the Northern Parula had reappeared in the large cottonwood on the left just as you head down from the bottom of the main grove.

John Luther and I decided to position ourselves slightly up the hill from that tree where we saw several warblers and flycatchers, but not the hope-for Northern Parula. Suddenly I noticed an unusual vireo foraging slowly in the middle of the tree. I called out, "Possible Yellow-throated Vireo," and pointed it out to John Luther who agreed with the identification. After another look, I announced the Yellow-throated Vireo on the radio and there ensued a considerable rush of birders, some of whom managed to see the vireo during the couple of minutes it was visible. Then, Tom Wurster noticed a short-tailed bird fly away down the canyon, that he thought might have been the vireo which was not seen again for quite a while.

After a couple of hours, and finally getting decent views of the Northern Parula, and American Redstart, I headed back up towards the pond where a Scott's Oriole was singing. There I heard the slurred phrases of a "Solitary" type vireo nearby, but the song stopped immediately. I pointed out the song to several birders including John Luther, but the bird did not sing again at that time. Eventually other birders arrived and I mentioned that I had heard a brief vireo-like song, but I was not prepared to say what it was. Since no other vireos of any species had been seen that morning, a good number of birders gathered in the area and John Wilson (I think) spotted the Yellow-throated Vireo. I went over by the pond where the crowd had gathered where Jeff Seay pointed out the Yellow-throated Vireo and we all got excellent views of the bird. Later it started singing quite a bit and as the winds calmed down, the vireo became very cooperative and easy to see.

It gave a throaty, widely spaced series of phrases that sounded typical to me, but it also gave another song that I thought was indistinguishable from Cassin's Vireo. In fact, one observer was quite sure that there was a Cassin's Vireo in the area, but I tracked down the singing bird which turned out to be the Yellow-throated Vireo. The following description is based partly on notes made immediately after seeing the bird.

Description

It had the large, rounded head and plump body shape and size of a "Solitary" Vireo, but with a green, unstreaked back and crown. The eyes were dark with obvious bright yellow spectacles and it had a yellow breast. The rest of the underparts were whitish, but decidedly grayish on the sides and flanks. The wings appeared blue-gray with bold white wing-bars. The thin tail was often cocked up at an angle as the bird foraged slowly in the Cottonwood leaves. The underside of the tail appeared gray with no tail-spots evident.

When the bird became more cooperative I was able to see the unstreaked, gray rump and uppertail coverts that contrasted with the olive-green back and I was able to confirm that the legs were fairly thick, sturdy and gray in color. The bill was quite thick and blunt looking, but when the bird was singing, I could see the slight hook at the tip of the bill.

Discussion

We returned to Butterbredt Spring the next day, and many birders were enjoying the Yellow-throated Vireo when we arrived. This is the sixth Yellow-throated Vireo I have seen in California. The others were at Deep Springs INY (May 1976), Point Reyes MRN (June 1978), Stinson Beach MRN (October 1992), Westminster ORA (January 1998), and the Big Sur River Mouth MTY (May 2001). I believe this is the fifth record for Kern County.

Additional information has been posted here.