When you see them together, there is no doubt which is the Greater or Lesser Yellowlegs.
Yes, size does indeed, matter. The taller a basketball player is, the greater advantage he or she has, all other things being equal; and at the Kentucky Derby, a jockey’s total weight, with outfit, riding equipment, and saddle, must come in under 126 pounds. Football players seem to be getting bigger every year, and tiny elfin gymnasts at the Olympics this summer will dominate our television screens. Surprise, surprise, size is important in the bird world, as well.
Without getting into the obvious differences between Sandhill Cranes and hummingbirds; or discussing the distinct advantages that large raptors have over their smaller counter-parts; or why some birds have long bills that are stocky/thin/straight/up-curved/down-curved, while others have short bills, (also sometimes stocky/thin/straight/up-curved/down-curved); or the escapability that smaller birds have when diving into a brush pile or thicket to avoid a hungry predator; this article will concentrate on the role size plays in simply identifying a bird and separating it from other similar species with which it might be confused. In fact, Peterson, in the introductory “How to Identify Birds” section to his field guide, begins with the first basic question: “What is the Bird’s Size.”
In field guides all species are drawn to appear pretty much the same size. Bird photographs, often without any scale for reference, depict birds in full frame so that it is hard to tell whether the bird is a jumbo jet or a Piper Cub. Only the written description in the accompanying text tells you the actual size. And that is very hard to visualize. In the field a larger shore bird with bright yellow legs is probably a “Yellowlegs,” but the question becomes, “Which one?” The Greater, 14 in. as the field guide says, or the Lesser at 10 ½ in. according to the “book?” Almost impossible, even through a telescope, until you see them side by side. Then it becomes obvious. Size does make a difference.
On Bird Identification class field trips the participants are often astounded that either Jewel or I are able to identify a distant flying bird as a Forster’s Tern, without even raising our binoculars or taking more than a sideways glance. Of course, we already know that there are only three species of terns commonly present in Florida in the winter when the classes are held, and that two of them, the Caspian and Royal are half again as big as the Forster’s (Royal and Forster's shown above left). This too, becomes obvious when they are seen side by side.
So the lesson, Class, is: that it is important to become familiar with the general size of the different species as they relate to other members of their family groups, whether they be herons and egrets, shorebirds, gulls and terns, raptors, and just about all the different bird families. Then test yourselves on the two remaining photos and see if the size difference of the three species of gulls, the two tern species, and the three species of shorebirds helps you identify them. I’ll try to think of an appropriate prize for the first reader who correctly names them all and lets me know. (5/15/12)