Scaup were my introduction to the true terrors of birding. For those who do not follow the sport, I should explain that scaup are ducks. Diving ducks, to be more precise.
If you are not into the topography of bird wings, I should explain that the secondary feathers are attached to the second joint of the wing. Think of a chicken wing. The second joint is the part with two bones in it. The primaries are attached to the third joint. On a chicken wing this is the short, pointed tip of the wing, the part with no meat on it.
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Of course if the birds fly, you do have that wing stripe to look at– but even that is hard to see. The next time a pair of mallards fly over, notice how fast they flap their wings. And mallards are dabbling ducks. Experienced birders can tell dabbling ducks from diving ducks just by noting the speed of their wing beats. Diving ducks flap their wings much faster than dabbling ducks. So fast, in fact, that measuring the length of the white wing stripe becomes very difficult. It is so difficult that I usually can’t do it unless I see the birds coming in for a landing and gliding on extended wings.
Biologists who study the question of how species originate talk about isolating mechanisms, factors that separate different populations of the same species. In time, these isolating mechanisms can turn two populations of the same species into two distinct species.
Habitat choice and behavior are also isolating mechanisms. Changes in courtship rituals or differences in the timing of mating may prevent individuals of the same species from breeding together. In time these separated populations could develop into different species like the greater and lesser scaup.
