Introducing the Farallon Yellowstart
September 13, 2020
In mid-August, most of the summer seabird crew departed and welcomed the fall migration crew. While there are still some seabirds nesting on the island, which we’ll continue to monitor, in the fall our research priorities shift toward monitoring the migrants on and around the island including bats, birds, cetaceans (dolphins and whales), pinnipeds (seals and sea lions), and white sharks. Our first couple of weeks were filled with wild weather such as unexpected lightning storms that later sparked the SCU Complex fires in the Bay Area, fog limiting visibility to a quarter of a mile, and howling northwest winds. But at the end of August, the winds subsided and shifted to the southeast, the fog lifted to overcast, and the nocturnally migrating songbirds that found themselves over the ocean discovered refuge on the Farallon Islands.
During the first couple of weeks, land bird diversity was mostly limited to nine Eurasian Collared Doves, but between August 29 and September 5, we saw 62 land bird species and 12 shorebird species on the island. Highlights included a Sora, a Long-billed Curlew , a Gray Flycatcher, an Eastern Kingbird, two Black-throated Sparrows, a Blackburnian Warbler, a Chestnut-sided Warbler, a Prairie Warbler, three Canada Warblers, and a Blue Grosbeak. In addition to these rarities, for the first time in many years, we saw large numbers of Olive-sided Flycatchers, Western Wood-Pewees, Yellow Warblers, and Wilson’s Warblers.
The most exciting migrant to show up was found by resident research volunteer Evan Lipton, when he spotted a weird warbler flying from the Heligoland Monterey Pine to a small brush pile. The tail pattern strongly suggested American Redstart, but the bird appeared oddly pale. As it hopped into view and perched on a branch, the bird suddenly looked more like a chunky, big-headed, small-eyed Yellow Warbler. For a moment, Evan thought there might be two birds, but the brush pile was tiny, and on closer inspection, the two looks were clearly of the same individual. The mix of American Redstart and Yellow Warbler features suggested a hybrid individual. The only hitch is that hybridization has never been documented between these two species.
Thankfully the bird lingered around the island for three days giving the residents opportunity to photograph and capture the bird. The Farallon Yellowstart, as we’ve dubbed it, appears to be the first well-documented occurrence of this hybrid between Yellow Warbler and American Redstart, and we hope to confirm who the parents were by genotyping the feather samples we took.
After this exciting start to the season, we have returned to foggy days, and many of the land birds have departed to continue their migration elsewhere. Though once the fog lifts, we hope to see more migrants hopping about the rocks and filling the sparse vegetation on Southeast Farallon Island. As always, you can follow us on our eBird profile page, where we post daily lists of birds seen.