"Group size definitely matters here. The bigger the crowd, the more it takes to stand out," Discovery News quoted her as saying. "Imagine if you hung out with the same three people every day. You certainly wouldn't need to dress like Lady Gaga to be recognized, but in a group of 50, 100, or more, it sure could help," she added.
Pollard and colleague Daniel Blumstein examined rodent species that included California ground squirrels, Olympic marmots, yellow-bellied marmots, black-tailed prairie dogs, white-tailed prairie dogs, thirteen-lined ground squirrels, Belding's ground squirrels, and Richardson's ground squirrels.
They caught individuals from each of these groups in a live trap. They recorded vocal alarm calls from each of these rodents and compared them to the alarm vocalizations of other members in that rodent''s particular social group. The results showed that the size of the groups predicted the uniqueness of each voice. The larger the social group, the more distinctive the voices were.
"Differences in rodent voices are much like differences in human voices. Some animals'' voices are high-pitched, others are low. Some voices are clear, others are more scratchy. Individual animals also have different timbre and use different patterns of emphasis. Each call has an animal''s unique vocal stamp on it," Pollard said.
"People often assume that our ability to recognize individuals is simply a consequence of natural biological variability in detectable physical traits found in any population of individuals in any species," said Michael Beecher, a professor of psychology and biology at the University of Washington.
"If this were true, it should be equally easy to distinguish among individuals of any species, so long as you have the requisite perceptual abilities of that species." According to the researchers, however, larger social groups make it more difficult to identify members, prompting the evolutionary drive for individual uniqueness. The study is published in the latest issue of Current Biology.
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