Young sac-winged bats jumble bits of adult-sounding calls into strings, say researchers who’ve recorded the babies’ vocalizations.
The pups make these jumbled noises without the usual contexts, and that’s babbling, contends Oliver Behr of the University of Erlangen-Nuernberg in Germany. The nonsense amounts to bat versions of the jabberings of human babies and young birds, he and his colleagues argue in the September Naturwissenschaften. “It’s the first example of babbling in mammals other than primates,” says Behr.
The new bat study focuses on Costa Rican colonies of Saccopteryx bilineata. A sac-winged male defends a roost that includes several females. The name sac-winged comes from little pouches in which males carry a slurry of genital secretions and urine. They wave these pouches at females in courtship displays (SN: 1/1/00, p. 7: Available to subscribers at Male bats primp daily for odor display.
One of the study’s coauthors, Mirjam Knörnschild, also of Erlangen-Nuernberg, says she wasn’t thinking about babbling when she started recording bat-pup sounds. She expected to find what biologists call infant-mother contact calls, animal versions of “Mommy! Mommy!”
Sac-winged bats vocalize during courtship or territorial spats. Babies also make sounds when they’re separated from their mothers. Some social calls include barks, chatters, and screeches low enough for people to hear, while other social sounds and navigational squeaks are above the range of human ears.
Bat scientists depend on recording devices that pick up calls across a wide range of frequencies.
Knörnschild recorded contact calls from bat pups but also found a variety of sounds resembling adult calls. “For a while, I doubted my ability to sex and age baby bats correctly because I kept getting recordings of female pups sounding like adult males,” she says. Finally, she thought of comparing those sounds with those of human babies repeating adult syllables willy-nilly.
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She observed, for example, that young female pups at times give the trill of courting males. Adult females typically don’t make that sound. The trills, Behr says, remind him of horse whinnies.
Bat pups also make the call that adults give during territorial disputes.
Furthermore, young bats interspersed elements of adult territorial and courtship songs amid echolocation squeaks.
Another researcher who’s made recordings of the same species of bats isn’t ready to call this babbling. Gerald Wilkinson of the University of Maryland at College Park says that he’s not persuaded that adult bats confine their calls to single contexts.
Michael Goldstein of Cornell University studies the imperfect sounds of human baby talk and the mispronounced tootlings of young songbirds. “If I walked down the hall saying ‘hamster, hamster’ repeatedly [with the] correct acoustics but not in the correct context … it might be acting weird, but it’s not babbling, per se,” he says.
However, he adds, “I think it’s OK for the definition to change for different species.”
Charles Snowdon of the University of Wisconsin–Madison adds a social dimension to the description of babbling. The infant marmosets that he has studied produce repetitive, jumbled sounds that, like human baby talk, prompt adults to respond. He says that he’d like to know whether bat pups’ vocalizations elicit a response.