AppearanceThe term "sac-winged" refers to small pouches on the wings of "S. bilineata". These sacs are used by males to attract females and to mark their harem territory. During daily grooming, males will fill these sacs with drops of urine and glandular secretions. During displays for females, the male will hover in front of the female and fan her vigorously to expose her to the scent of the mixture in the wing sacs. Males will also shake the contents of the sac towards bats outside of the male's harem territory to warn off intruders. Microbial fermentation in the sac may produce identifiable sent signals. Sac-wing pups have been recorded vocalizing various calls and sounds in a jumbled context. For example, a female pup will give the male trill of courting followed by echolocation clicks then adult territorial challenges. These mixed-up vocalizations have been equated with human infant babbling and mispronounced songs of young birds. This is the first example of mammal babbling outside of the primate order.
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