Oct. 31, 2008 -- Their blood-sucking ways may terrify potential victims, but white-winged vampire bats enjoy such close and cuddly relationships with other members of their roost that they sing well-coordinated duets with each other, according to new research.
The study, which has been accepted for publication in the journal Animal Behavior, presents the first evidence for duet singing by adult bats. Such singing, technically referred to as "antiphonal calling," has previously been reported in two other bat species, but only between mother bats and their pups.
White-winged vampire bats, the closest living relative of the common vampire bat, appear to keep on singing into adulthood.
"The calls are audible to the human ear, although we can only hear part of the whole sound," lead author Gerald Carter told Discovery News.
"They sound like high-pitched chirping, alternating from different bats," Carter, a University of Western Ontario researcher, added.
He and his colleagues conducted several experiments on 18 white-winged vampire bats, some of which were wild-caught in Trinidad, but are now housed in a temperature and humidity controlled facility in New Mexico.
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Live chickens -- the favorite victims of the bats -- were herded into cages each night to serve as "blood donors," with no chicken parasitized more than once every eight days.
The bats became very vocal when chickens were around.
"They might be calling other individuals, such as kin, over to share, or they might be saying, 'Stay away, this chicken is mine,'" said Carter. "It's mostly speculation at this point."
The researchers were more interested in how the calls might function when individual bats were separated from their roost mates. When removed from their group, single bats remained silent, but when the lights turned off they called out like crazy. Their fellow roost members responded with remarkable precision.
"The responses are precise in time, about one-third of a second after the first call," explained Carter, who added that such duets were known to occur among primates, birds and elephants, but never before among adult bats.
After recording and analyzing the bat calls, the scientists further determined that each vocalization had its own unique sound structure. Members of the same roost could even link songs to the correct singer when the caller was completely out of view.
Carter and his team therefore believe the duets permit separated bats to reunite, with a little responsive singing help from their friends.
He thinks each call might communicate the individual's identity, location and feelings.
"It might be analogous to a person yelling, 'Hey! Hey! Hey!'" he said. "While there's still no distinct information in that message per se, a listener could still potentially determine who the person is, where they are, and how they feel."
John Ratcliffe of the University of Southern Denmark's Center for Sound Communication also studies bats. He told Discovery News that the new study presents "truly fascinating" findings.
Ratcliffe even thinks the bat's thirst for blood mixed with its charitable ways could be connected to the impressive duets.
"White-winged vampires are one of a very few species of obligate blood feeding vertebrates in existence today, likely a reflection of the difficulties associated with securing a stomach's worth of blood from a living, breathing -- and surely unwilling -- large bird or mammal," he said.
"In the wild, successful vampire bats sometimes share blood with their unsuccessful roost-mates," he added. "Such unselfish behavior is rare in animals and the current study intimates that reciprocal altruism among unrelated individuals may be mediated, in part, through vocal identification of individual roost mates."
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