Snuggled tightly together, three baby red bats hang in near-total silence amid the leaves all night long. Exposed among the tree’s foliage, their tiny bodies look like dead leaves or dried fruit, and that is their only protection against a host of predators.
Then their mother returns from a night of foraging. As she comes near, she makes a distinctive call that alerts her pups. She hangs alongside them, rubs her muzzle against them, licks their faces and uses her wings to nudge them into place for nursing.
The hungry pups cling to mom with one foot, generating a few calls and mechanical clicks as they prepare to nurse. Then both babies and mother typically make a faint humming sound, almost like a cat’s purr, that’s associated with a gentle vibration. The family of eastern red bats will spend the day together in the foliage, snuggling, humming, grooming and nursing.
Compare this with the incessant clamor inside a nursery cave used by colony-forming species, such as the Mexican free-tailed bats of Texas’ Bracken Cave. These mothers have just one pup per year. They deposit their babies in nursery areas where many thousands of pups – as many as 500 per square foot – are packed on cave ceilings and walls. The millions of mothers and pups in the cave socialize, groom, chatter, move about and generally maintain a continuous din.
When moms are ready to nurse, they must somehow locate their own pups amid the mob of squirming infants. Mothers produce repeated “directive calls” while hungry pups get mom’s attention with “isolation calls.” Both seem to be vocal signatures that help mother and offspring locate each other.
Colonial bats are extremely social animals with at least 20 distinct calls, and they live in relatively protected roosts. Red bats spend most of their lives alone, except while mating, rearing young and, sometimes, during migration.
BCI Science Officers Barbara French, Biologist Erin Gillam of the University of Tennessee and M. Brock Fenton, Biology Chair at the University of Western Ontario, studied mother-pup vocalizations in captive eastern red bats. They identified only six distinct calls strong enough for analysis and found far less sophisticated use of vocal communication among red bats than Mexican freetails.
Much of the reason for the fewer, softer vocalizations probably is because of the more solitary existence – and the much greater exposure to predators.