January 6, 2008
Gull, you really got me going
I am not a gull person, though I'm often mistaken for one by other non-gull people.
Come winter time there's not much to do on cold, rainy days except go to the gull fields and sort through gulls. I do it because gull ID skills are a useful part of any birder's tool kit, but I have no passion for it. This gives me an advantage most of the time over gull haters (misogonyists) and gull lovers (larophiles), because I tend not to complicate things.
I fully expect to get arguments from both camps, but I think gull ID is mostly straight forward. Once one knows the basics, well over 90% of all the gulls I see can be identified with high confidence and little consternation. Yesterday, at Wireless Rd, there were about 5000 gulls pecking at the bits of dead fish scrap dumped there by farmers. All the small ones were Mew and Ring-billed Gulls and most of the large ones were Western or Glaucous-wings (or some genetic combination of the two) with a healthy scattering of Herring Gulls. From a statistical point of view, 90 to 95% confidence for the composition of a flock is a good thing. One would think that would be satisfactory.
Truth be told the only times I really get in trouble over gulls is when I try to over complicate an ID by getting hung up on a single fieldmark and stop looking at the whole bird.
But sweating over the outliers is what we birders do and that's why folks who love gulls talk about subtleties of head shape, the Kodak gray-scale, orbital ring color and gonydeal angle and why gull haters lobby for lumping larids.
In the Wireless Rd flock, there was also one Glaucous Gull and a couple of likely Glaucous X something hybrids. Missing the single Glaucous Gull does not rip a hole in the fabric of winter gull distributional biology nor does misidentifying a Glaucous hybrid as a pure Glaucous. As far as hybrid ID goes, the game of who's-your-daddy is so fundamentally insoluble away from the breeding grounds that fussing about hybrids just makes gull ID unnecessarily arcane. And it frightens the straights.
At the genetic level, most of the so-called large white-headed gulls are such a mishmash of variability that it's often difficult to assign species status to individuals (Hebert et al. 2004). In some cases individuals within a population of a single species show as much variation as individuals in populations defined as different species. This is largely attributed to fairly recent evolutionary divergence of the component populations that form the white-headed gull superspecies complex.
This lack of genetic clarity works well for the lump larids camp, but there's something fundamentally counterintuitive about claiming Mew Gulls, California Gulls and Glaucous Gulls are all the same thing. Gulls turn out to be a case where what one sees in the field is more representative of species differentiation than what one sees in the laboratory blender. It's old-school taxonomy at its most powerful. Morphological, behavioral and ecological differences count for something that hasn't yet materialize at a resolution genetic markers can reliably demonstrate. So, there is value in being able to sort gulls, but genetic muddiness also plays itself out in the field. Even the purest looking of Western and Glaucous-winged Gulls out in the fields of Wireless Rd are probably carrying bits and pieces of genetic sins-of-the-father (or grandfather). There comes a point where the claims we make about what we're seeing are more faith-based than data based.
Anybody can learn the basics of Western/Glaucous-winged ID. Anybody can learn how to spot Mew Gulls and Ring-bills. And that gets us almost every gull we're likely to encounter in a field in the dead of winter. A bit of extra work on the beach in the summer will nail down California Gulls. Any birder who can confidently identify the Western/Glaucous-winged complex, California Gulls, Ring-billed Gulls and Mew Gulls is in pretty good shape and shouldn't let themselves be intimidated by the folks who choose to spend there free time sorting through the flocks for the rare (and potentially interesting) outliers.
Missing the odd 2nd-cycle vega in among the smithsonianus will not be the end of the world. Ninety percent confidence in anything in life is something to celebrate.
Posted by mbalame at January 6, 2008 10:25 AM