January 29, 2009
Variations on a theme
Oh no! not another post about gulls! It must be mid-winter...
I spent yesterday morning meditating on what it means to be an Olympic Gull. Those of you who spend any time with Pacific Northwest gulls know that we live in the center of a hybrid swarm between Western Gulls and Glaucous-winged Gulls up here on the Columbia River Estuary and the complex is referred to in the literature a "Olympic" Gull. This is a fairly well studied hybrid swarm as it turns out with data going back to at least 1978 (Hoffman, Wiens and Scott, Auk 95:441-458) and more recently from Douglas Bell (1996 Condor 98:527-546 and 1997 Condor 99:585-594) mapping out the extent of the zone of sympatry.
With gulls, the simplistic version of Mendelian genetics we all learned in High School does not do the complexities of a hybrid swarm justice. For one thing, gull hybrids are fertile and under some circumstances may even be more viable than "pure" Westerns or Glaucous-wings.. This means that hybrid individuals can mate with "pure" individuals and with other hybrids. The result of all this inter-breeding is a mish-mash of phenotypes grading from apparently pure Western Gulls through all sorts of intermediates to apparently pure Glaucous-winged Gulls.
I'll let those who are interested reading about the details of why a more or less stable zone of hybridization even exists sort through the relevant source material at SORA and stick to my original train of thought: How can a natural population of organisms be so ubiquitous and still be dismissed as valueless because it's not a real species?
You see, we birders are not allowed to count intergrades on our official species lists. If one travels far enough to the north or south, the number of intermediates drops to a point where any discussion of purity almost disappears. But here in the thick of the intergrade murk we have to think about what we're seeing and more importantly, we have to think about what we're going to tell the folks from out of town who've come to add Western Gulls and Glaucous-winged gulls to their species lists. After all, 60 to 80 percent of the gulls we're looking at exist in an uncountable limbo. When we do give them a really good look, it's in an effort to turn them into a Herring Gull or a Thayer's Gull and when the "truth" is revealed it's "oh, just another hybrid."
The really serious gull folks have a vocabulary of terms that describe shape and size and posture and angle to sort through gulls and it's very useful, if one wants to travel the globe building up a gull list. But the kind of devotion necessary to be a true gull master requires way more time and energy than most of us are willing to give. And if the only goal for internalizing all this arcanery is to be able to say "it's just another hybrid"... well that strikes me as sort of snobby.
There is simpler path.
Rather than fixating on the name of each and every gull, which in the midst of our hybrid swarm, may not even be possible, focus on understanding the variability within the swarm. Biology, after all, is more than the naming of parts. Gull taxonomy is in a state of flux, both biologically and academically speaking. Sometimes there's more to be gained by watching the dynamics of a population than making sure each individual within it has been tagged correctly. There's value in spending the day looking for relevance among the uncountable...
Update: Wayne Hoffman, who co-authored the 1978 study of "Olympic" Gulls sent the following comment: "Study of "Olympic Gull" hybrids actually goes back to Dawson's Birds of Washington, in 1909."