Birdwatchers know that male loons have characteristic calls that remain relatively stable from year to year.
But a new study has found that when a male loon (see photo) changes territories to find a new mate, he changes his call, too. Why this happens is a mystery.
Charles Walcott, a biologist at Cornell University in Ithaca, New York, lead the research, which focused on loons in a Michigan wildlife refuge.
Walcott explains that the male's call—or yodel—is highly significant for other males, and scientists have decoded only part of it.
"The yodel is an important signal from one male to another," Walcott said. "We know that the yodel codes for the size of the loon—the bigger the loon, the lower [pitched] the yodel.
"As the loon loses weight over the years, the pitch changes and goes up. The loon is effectively advertising how susceptible he may be to a takeover."
But through careful observation and recordings, Walcott has found that much more radical changes in the loon's call occur when the bird changes territories, moving to a new lake or a different part of his home lake.
The study appears in the March issue of Animal Behaviour.
Hear the Difference
Walcott and his team recorded the yodels of loons on 21 artificial lakes at the Seney National Wildlife Refuge near Seney, Michigan.
The researchers recorded the calls of individual loons in one territory, and then rerecorded the same birds in the new territory to see how their calls changed.
Walcott and his colleagues succeeded in recording calls for 13 male loons before and after they moved. In 12 of the 13 cases, the loon's call changed when he took over a new territory.
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