The recent occurrence of a Taiga Bean Goose (Anser fabalis middendorffii) at Unit 1 of the Sonny Bono Salton Sea National Wildlife Refuge has sparked some discussion about speciation and vagrancy of geese. Like most southern California birders, we went out to see the bird. As rarity chases go, this one was somewhat underwhelming. A 180-mile drive brought us to Vendel Road at about 6:20 a.m. to where a group of birders had already assembled. The bird was in view as it quietly fed with the three Greater White-fronted Geese that form its posse. As it was a good 200 yards away in a field full of deep furrows, we seldom saw more than its head and neck. Once, it walked up on top of a furrow, and showed off the bright white feather edging in its back and wings. But that was about it.
While we viewed the Bean Goose, behind us in a nearby pond was a large mixed flock of Snow and Ross’ Geese (ignoring the Four Horses of the Apostrophe in favor of better English) containing one obvious blue-form goose, which was a Ross’ Goose. This prompted local bird expert, Bob Miller, to observe that, globally speaking, a blue-morph Ross’ Goose is rarer than a Middendorff’s Bean Goose. Sure. Okay. Wait a minute… What?! Well, the world population of Middendorff’s Bean Goose is roughly 5000 birds. According to McLandress & McLandress (The Auk, 1979, vol. 96, 544-550), blue-morph Ross’ Geese constitute approximately 0.02 % of the total population, which at about 1,000,000 birds means there are maybe 2000 of them. So, globally speaking, a blue-morph Ross’ Goose is actually rarer than a Middendorff’s Bean Goose. Then again, in recent years, blue-morph Ross’ Geese have been annual at the Salton Sea in winter whereas Taiga Bean Goose is usually a bit less reliable there, a reminder that in listing (and not just for real estate agents) it’s location, location, location! Which brings up another subject: there is a hunting season out there and it’s on now, so if you’ve a mind to, you might want to go see this goose sooner rather than later since it could end up cooked!
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