Oct. 31, 2007 -- Bat calls serve to identify each individual in a group, but twin bat siblings sound so alike that researchers are starting to suspect the calls also carry information about familial relationships.
A new study on the matter, which has been accepted for publication in the journal Animal Behavior, adds to a growing body of evidence that bats are social, vocal creatures able to communicate with each other in complex and detailed ways.
Lead researcher Mirjam Knornschild and her team focused on the calls of Nyctalus noctula, a medium-sized, insect-eating bat from Europe. Only the pups emit the "isolation" calls that were the focus of the study, which are low in frequency and are often repeated in succession, not unlike the repetitive cries of human infants.
"Isolation calls of Nyctalus noctula convey the pups' wish to nurse, their current location and also their individual identity," Knornschild, a researcher at the University of Erlangen-Nuremberg's Institute for Biology, told Discovery News.
She and her colleagues recorded young twin bats from a colony of captive bats at the university. The parents of the twins sustained previous injuries in the wild that prevent them from flying, but otherwise they exhibit normal bat behavior.
The twins were separated from their mothers for a maximum of 15 minutes and placed in a sound-proof chamber, where the recordings were made. The researchers also recorded the isolation calls of other, unrelated pups. Recordings were conducted when all of the bats were 1, 3, 9, and finally, more than 19 days old.
The calls revealed that all baby bats have distinct cries, but twins sound alike. As bats get older, their isolation calls become even more distinctive, but twins retain their vocal connection.
"A similar phenomenon could occur in other bats, or even in other mammals because twins not only share the same environmental factors while growing up, but also (may) share the same genes," Knornschild said.
In a crowded roost full of bats, a mother's ability to identify her offspring is critical so she can find, nurse and care for her pups.
Barbara French, a biologist and science officer at Bat Conservation International, was not surprised to learn that bats, even baby ones, emit information-rich calls.
"Adult bats make social calls, many of which are within the range of human hearing," she told Discovery News. "You can hear them chirping, trilling, beeping and buzzing away when they are with each other. I often wonder what they're saying."
She said male bats also sing courtship calls, with each song containing its own unique stamp of identification.
"It's as though a male sings his song and then adds, 'And by the way, I'm Bob,'" French said.
As opposed to more solitary species, colonial creatures like bats need to constantly identify themselves and share other information with each other, French explained. That is one reason why bats, from pups to adults, are so vocal.
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