By David Spector Gazette Contributing Writer
One of the pleasures of being a biologist is exercising my curiosity about the natural world. Sometimes I come up with satisfying answers, while at other times I simply get to enjoy exploring the questions. Another pleasure comes from the chance to do this without leaving my yard.
Perhaps everyone who sees migratory birds returning to a spot in the spring wonders if they’re the same individuals who nested there the previous year. Small birds face many hazards; as many as half the members of a population may die in a typical year, so it’s remarkable that they not only survive but come back to the same place. It’s difficult to know for sure, but last year I had reason to believe that at least one bird was the same I had seen the previous year.
Eastern phoebes—rather plain, gray, insect-catching birds—came back to my house last spring, used the porch railing for launching attacks on insects, and quickly built a nest in the same location that was used the previous year, under the front porch. The fact that the birds used the same hidden site suggested that one or both were familiar with it.
Why use the same site? The reason likely lies in numbers. Birds returning to the same spot and the same mate can get started nesting quickly. A fast start on nesting means that a pair may be able to raise two, or even more, clutches of young in one breeding season. Since many nesting attempts fail because of predators or weather, an early start gives the parents a better chance of at least one successful nest.
As I watch these neighbors, a more challenging “why” arises. The phoebes on the porch railing often show their characteristic tail-wagging. Why do these birds wag their tails so frequently? They do it so often that bird-watchers use it as one way to identify this species.
Many birds wag their tails to help stabilize themselves, especially at landing. Birds of a few species continue to wag their tails even when perched for long periods. Why continue to wag? One possibility, of course, is that the birds have poor balance, but the fact that a phoebe wags its tail even when perched on a stable railing suggests that lack of balance isn’t the issue; communication offers another possibility.
University of Pennsylvania biologist W. John Smith spent many hours in the 1960s and ’70s watching Eastern phoebes to try to understand their behavior. He concluded that tail-wagging conveys information about indecision and the probability of flight, much as a gesture like head-scratching or brow-furrowing might convey human indecision and the possibility of a change in behavior.
But questions remain: What advantage does a bird gain by sharing this information? How do other phoebes use this information? Perhaps the tail waggers are demonstrating their alertness.
I could think of many experiments and observations that might provide useful evidence for answering these questions, requiring years of intense effort. For now, though, I can just appreciate that a glance at my porch railing provides enough questions for a lifetime of thought and observation.
David Spector is a former board president of the Hitchcock Center for the Environment and teaches biology at Central Connecticut State University.
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