Tilden Nature Area, Contra Costa, California, US
Sep 1, 2017 8:30 AM - 11:30 AM
Golden Gate Audubon Society First Friday Birdwalk, September 1, 2017. Tilden Nature Area, to Jewel Lake and back again.
Today's theme was Migration. None of the usual suspects have arrived yet: no records at eBird through the end of August of
ducks (other than Mallards), no kinglets yet, no Hermit Thrush, no Yellow-rumped Warbler, no Fox Sparrow, no White-crowned or Golden-crowned Sparrows. Wintering birds that have arrived are Townsend's Warbler (came in mid-August) and that's it! First week of September is historical arrival time for Golden-crowned Kinglet and Fox Sparrow.
Cornell's third edition of Handbook of Bird Biology shows our Fox Sparrows are part of a "leapfrog migration" pattern: Birds of the Alaska Peninsula and Aleutian Islands go to Channel Islands and L.A.; birds of Yakutat Bay area where the Yukon meets Alaska come here to Tilden Park; birds of the Alexander Archipelago (Juneau and vicinity) go to Humboldt and Del Norte counties and southern coastal Oregon; and the Vancouver Island population stays put! So, the furthest north Fox Sparrows go the furthest south.
Swainson's Thrushes in North America have two migration routes and two overwintering sites: Pacific Coast thrushes go to Central America; Alaska and inland Canada thrushes go to South America. These populations meet (overlap a bit) in British Columbia and show some hybridization in the Coast Mountains, but there is not a lot of mixing. Maybe Swainson's Thrush is well on the way to forming two species?
Since 1980 (when 6 pairs of Barn Swallows were found nesting under a bridge in Buenos Aires Province after all the other Barn Swallows had gone back to North America), a population of Barn Swallows has been established that breeds in the austral summer and doesn't return at all to North America. And new "dropout migrants" have added to the population!
Highlight of today's walk was a banded Wilson's Warbler (left red over red/ right silver), probably from Dr. William Gilbert's study, seen at the entrance to the Tilden Nature Area.
Thanks to the 36 attendees and Erica K. for the warbler close-up.
Here are the 22 species seen by our 36 observers:
Turkey Vulture makes it official
Nuttall's Woodpecker newly revised account is at Birds of North America (July, 2017)
Hutton's Vireo We heard the call that John Robinson calls "pig squealing in a tree". Listen to ML 120200 at the Macaulay Lab by Geoffrey A. Keller, from 2002. This call may be in response to intruders (us!).
Wilson's Warbler Banded bird, left red over red/ right silver, probably from Dr. William Gilbert's ongoing study.
Best of Boids!
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