Loons Change Tunes After Finding a New Home, Study Finds
for National Geographic News
|April 11, 2006|
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 callor yodelis 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 loonthe 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.
The loon's call consists of two parts, an introductory "phrase" followed by a highly variable number of repeat phrases.
(Hear the call of a male loon before moving to a new territory.)
The researchers distinguished between calls by noting changes in the frequencies of the first phrase and alterations in the gaps between the following repeat phrases.
(Hear the same loon after moving to a new territory.)
Alec Lindsay, professor of biology at Northern Michigan University in Marquette, sees the discovery as evidence that loons are bird-brained only in the most literal sense of the term.
"For me," he said, "this study is an elegant demonstration of the complexity of a loon's brain. These animals don't just have inflexible vocalizations that they use for 25 years.
"They're doing some pretty complex interpretations of their social environment and modifying their behavior accordingly."
Loon pairs may live together in the same territory for as long as 20 years, which is half or more of the birds' lifetimes, Walcott says.
But the male and female remain independent and often look for new territories and mates.
The changes Walcott's team found took place when males flew around looking for new digs.
Lindsay said that previous work with loons hasn't looked at the effect of territory change on the birds' calls.
"People would say anecdotally that they could tell the difference between loon calls from different lakes," he said, "and that sort of anecdotal report made researchers want to look at this."
No one knows why loons change their tunes after moving.
Walcott first thought that females might prefer a certain call and that newly arrived males changed their yodels to accommodate them.
But males sometimes stay in the same territory and acquire a new female. In such cases, the male's yodel stays the same.
Then the researchers hypothesized that a male may change his tune to try to sound like one of the locals.
Wrong again. The changed calls were not imitations of the previous residentthey were always different.
Not all experts are convinced that a change in vocalization has any survival value or evolutionary significance.
"If this gave an advantage, then one would expect to see all males changing calls annually to gain this benefit," said Martin Fowlie of the British Trust for Ornithology, a bird-research nonprofit based in Norfolk, England.
"More research and experimental manipulations may give some insight into the adaptive significance of this change."
While the full significance of the call of the male loon is still unknown, it's clear that it is full of meaning to other loons.
"[A male in a new territory] must know the previous resident's yodel," Walcott said.
"And that's a surprise, too. It almost seems they're planning their moves. They spend time flying around, listening to responses to their yodels and strategizing about what it makes sense to do."
Lindsay, of Northern Michigan University, sees this work as an important contribution to the study of loons.
"These are charismatic birds," he said, "and they're fitting indicators of the health of our natural environment. I hope this study will encourage further work on these complex, long-lived birds."
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