As birders learn to look closer, we more and more detect birds that somehow don’t fit the categories of the birdy books. Individual variation accounts for some of that, but many of the odd birds we encounter are, or at least seem to be, hybrids and intergrades, the products of matings more enthusiastic than accurate.
Some such hybrids are pretty obvious, like this apparent Mallard x Northern Pintail.
In many cases, though, the putative parent species are so similar to begin with, and their offspring so variable, that distinguishing between a “pure” individual and a hybrid can be a real challenge.
This gull at Clover Point this past weekend, for example, showed the mix of Western and Glaucous-winged Gull characters typical of our local “Puget Sound Gull”: a darkish mantle, blackish wingtips above, faintly marked wingtips below, and an orbital ring mixed yellow and red.
And this goose, hanging out in a Tucson park this winter, is probably a Ross’s Goose — or the long bill with a slight “grin patch” might suggest hybrid ancestry.
These are old stories and familiar, but lately I’ve been thinking about when birders look for (and find) hybrids. What it comes down to is markedness, or which potential parent taxon is deemed the default. This varies geographically, of course: in the east, a reddish Northern Flicker will be scrutinized, while over much of the west it’s the apparently yellow-shafted birds that draw special attention.
But I don’t think that markedness is always just about rarity and vagrancy. Even in those areas–and there are more and more of them as time goes on–where, say, Snow and Ross’s Geese are equally expected, it’s only the apparent Ross’s that are inspected for signs of hybridization: how often have you heard anyone cautiously report “an apparently pure Snow Goose,” even in places like southeast Arizona where both white geese are uncommonish? Nobody ever objects that a tentative Snow Goose’s bill is a bit short or the head a bit round or the plumage a bit white.
Even more strikingly, here in Vancouver I notice that birders (by which I mean mostly myself) readily pass over the slightly uncommon Myrtle Warblers, while subjecting the more abundant Audubon’s Warblers to a much more thorough examination. Adult male Audubon’s types with white in the throat or lightly marked wing coverts? Probable hybrids! But I simply tick the Myrtles; even when I linger over a particularly snazzy one (they are really very beautiful), I more often than not wind up moving on without checking it over at all as carefully as I do the yellow-throated birds. But surely there are hybrids that more closely resemble Myrtles than Audubon’s, aren’t there?
The lesson that I’ve drawn from these musings? Start to treat all the birds I see as “marked,” as potentially something different and weird–as worth looking at more closely than I already do. Who knows what I’ll find now?
