WINTER 2007/VOLUME 21, NUMBER 1
Caller ID for Crows
Sound analysis shows subtle differences in the alarm calls of individual crows
Most of us would know our mother's voice on the phone from the first syllable uttered. But can birds such as crows recognize the voices of their relatives—even if their caws all sound pretty much the same to us? A new study suggests they may.
By recording and analyzing the alarm caws of American Crows, Cornell undergraduate Jessica Yorzinski found subtle acoustic differences that crows might use to recognize who's calling. Published in The Condor (August 2006), the study suggests that this ability could be particularly important for crows because they interact with family members throughout their lives.
"Lots of crows end up breeding in the neighborhood they grew up in so there is no doubt in my mind that they recognize each other. How they do that, we have no idea," says coauthor Kevin McGowan, who has studied the family lives of crows for 18 years.
Crows are social birds that often hang out in family groups. Though they look alike to us, individual crows can probably recognize one another.
To find out whether vocalizations might be a cue, Yorzinski looked for variation in the calls that crows make when alarmed. She recorded crows around Ithaca, New York, that had been individually marked with tags as part of a long-term study by McGowan and coauthor Anne Clark of Binghamton University.
"One of my main groups of crows hung out near Barton Hall near the center of the Cornell campus," says Jessica. "It could be pretty tricky recording the birds there because of all the traffic." She found quieter surroundings by recording another family of crows in a cemetery.
When Jessica approached the crows with her recording gear, they would often become nervous and sound the alarm. In all, Jessica recorded more than 10,000 alarm calls of 15 crows from 5 family groups.
Using a sound analysis program developed by the Cornell Lab of Ornithology's Bioacoustics Research Program, Jessica measured more than two dozen acoustic features of a subset of these calls, including frequency, duration, bandwidth, and energy distribution.
She found seven features that differed among individuals—differences that the crows could potentially use to recognize one another's calls.
This ability could be useful in deciding how to respond, since some callers may be more reliable than others. Young birds, for example, might use alarm calls even when little danger is present.
Jessica also found notable differences between the calls of males and females. "It was surprising because when I went out in the field I didn't know which birds were males and which ones were females," Jessica says.
She only realized there were clear differences after DNA analyses identified the sex of each crow. Female crows had higher-pitched calls that sound shriller to human ears.
However, one male crow that had moved in from a neighboring family uttered alarm calls that fell in the female acoustic range.
"We did DNA testing twice to be sure this bird was a male," McGowan says. "Our speculation is that he is subordinate and perhaps he's talking 'baby talk' in order to get accepted." McGowan explained that in many bird species, a newcomer tries to gain acceptance from dominant birds by begging and fluttering its wings like a young bird.
"I definitely think it would be interesting to follow up on the subordinate-dominant issue to see if that holds true for other birds," says Yorzinski. A logical extension of her work would be to analyze other types of crow vocalizations to get a better idea of the cues they may be using to identify whether a friend or foe comes cawing.
Jessica Yorzinski conducted the study as a Cornell undergraduate. Her mentor and coauthor, Sandra Vehrencamp, is a researcher in the Lab of Ornithology's Bioacoustics Research Program. Jessica is now a graduate student at the University of California, Davis, studying the mating choices of peacocks.
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