The limitations of Structure

(Written with some irony as I'm a Structural Biologist so quite a firm believer of the importance of structure at the atomic level).

The publishing of the O'Brien-Crossley-Karlson Shorebird Guide brought with it some fanfare of improved methods of ID by "birding by impression". I'm perhaps not as impressed as I could be by that idea, because I don't think it's novel - anyone that's spent any time birding is using structure (shape and posture, but also intangibles of behavior) anyway.

Since I belong to the often thought-provoking BIRDWG01 "Frontiers of Bird Identification" email list it's often very interesting to think about the discussions on there. In particular it's apparent that the structural appearance of a bird is often very heavily influenced by the posture that the photograph captures. It may be "typical" or "atypical" viewed through birders' eyes. I've developed an internal idea about how birders select ID point, which in terms of structure involves discarding a whole range of ambiguous views (or perhaps integrating them mentally) until a distinctive view is found from which one can make the ID. A photograph presents only one or a small number of views, and mayhem seems to sometimes break out by experienced birders trying to hammer the square peg into the round hole: an anomalous view of a typical species.

Although color perception may be skewed by lighting in photographs (or to a lesser extent by post-processing), I find that structure is especially vulnerable to this. I've seen shorebird structure vary all over the place in a series of photographs. To whit: two recent BIRDWG01 discussions on a bright alternate White-rumped Sandpiper from Canada and a first fall immature Sanderling from Bolivia in prebasic molt. In both cases one of the strongest proponents of structure as a primary ID point identified the former as Western Sandpiper and the latter as White-rumped. Whoops. Particularly in the latter case where I was induced to go dig out my own photos of the White-rumped & Sanderling group to check my overall impression (color and bill structure) against the photographs. And it looked even more like a Sanderling after that exercise than it did on my first impression. Plumage coloration and pattern were definitively Sanderling from my perspective.

Which leads me to suggest: structure is overrated, particularly when identifying from photographs. Often very important, sometimes definitive, but also perhaps overrated and certainly not revolutionary. Birding has been going on for too long, practiced by too many people, for anyone to come along with revolutionary ID points across entire classes of birds. While genetics may radically revise how we view species distribution and what it means to be a species, I somehow doubt that morphological considerations are going to overwhelm those of plumage color and pattern any time soon.