Monday, August 16, 2010
Yellowlegs, more and less.
Migrating Greater and Lesser Yellowlegs can often be seen together, which helps with the identification of any particular bird. Above, note the relative stockiness of the front bird, and most importantly, the relatively heavy, long bill (greater than head length) that turns up slightly at the tip (= Greater YL). In the farther bird, the bill is relatively shorter (approx. = head length) and more delicate (= Lesser YL). The body size in the nearer bird is also greater (length 14" vs. 10.5 "), but this is a better character when the birds are equidistance away.
The Greater was actually on his own, and just happened to be striding through a small flock of Lessers as I passed by with my camera.
Interesting phylogenetic hypotheses: The sister species of Lesser Yellowlegs (Tringa flavipes) is the very different-looking Willet (T. semipalmata). Thus Greater and Lesser Yellowlegs are not each others' closest relatives. Greater Yellowlegs (T. melanoleuca) is more closely related to the Old World Common Greenshank, (T. nebularia). I don't have access to the primary literature, but a relevant reference is cited by Wikipedia:
Pereira, S. L., & Baker, A. J. (2005). Multiple Gene Evidence for Parallel Evolution and Retention of Ancestral Morphological States in the Shanks (Charadriiformes: Scolopacidae). Condor 107 (3): 514–526. DOI: 10.1650/0010-5422(2005)107[0514:MGEFPE]2.0.CO;2 Abstract.
Additional thought: What is the plural of "Yellowlegs?"