Sing a Song of Natural Selection
Story posted September 15, 1999
Nat Wheelwright, professor of biology and director of the Bowdoin Scientific Station on Kent Island, posed the following question at the Sept. 15 Faculty Seminar: “Do Birds Use Song to Recognize Relatives and Avoid Incest?” He confessed to having not yet discovered the answer, but he offered several intriguing insights into bird behavior that might help lead him to a conclusion in the future.
Wheelwright said the question of how a female chooses a mate has perplexed him since junior high school. In his professional life, however, he has concentrated on the habits of birds.
Avoiding inbreeding is important to the survival of any species, because inbreeding leads to a higher mortality rate. Wheelwright said it is important to understand how animals avoid inbreeding because the risk of it increases as animal habitats become more fragmented.
Wheelwright and his students have spent the last 12 years netting, banding and tracking about 12,000 savannah sparrows on Kent Island in the Bay of Fundy off Nova Scotia. So far, these sparrows seem to have avoided the pitfalls of inbreeding: In 1,050 matings Wheelwright recorded, there were no cases of inbreeding. That is statistically unlikely considering their tight habitat and propensity to breed in the same area where they were born.
Scientists know that birds do in fact recognize their relatives, and even distinguish among the closer and more distant relatives: They treat siblings better than they treat cousins, for example.
“How can they possibly tell who their relatives are?” Wheelwright wonders. He believes their songs may be the key.
Using special microphones, Wheelwright and his students have recorded the songs of the male birds (only males sing) and fed the recordings into a sound spectrogram machine that creates printouts based on the tone and duration of each trill, buzz and whistle the bird produces. Each bird produces a song that is as unique as a fingerprint, and which remains the same throughout its life. The songs of sons are similar to those of the fathers, with slight variations added by each successive generation.
One hypothesis was that female birds learn the songs of their fathers and avoid them in choosing a mate, but they do not seem to avoid males with songs that are similar to their father’s.
They seem to avoid only their actual relatives.
“Maybe we’re measuring the wrong aspects of the songs,” Wheelwright said. “Or maybe the birds use pheromones. Or maybe our sample size is too small.”
He plans to leave soon for Kent Island to continue his search for answers.
Wheelwright’s was the second in this semester’s Faculty Seminar Series, weekly seminars that occur each Wednesday from 12:30-1:30 p.m. in the Main Lounge of Moulton Union. The seminars are open to all faculty, staff and students.
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