June 7, 2023

Large sac-winged bats are every field biologist’s dream. They hunt insects at dawn and dusk, stay awake for most of the day and rest at night.

“They like pretty well-lit places,” says Mirjam Knörnschild, behavioral ecologist at the Museum für Naturkunde in Berlin, who studies the bats that nest on trees or building walls and not in gloomy caves filled with guano.

And the bats, about five centimeters long, keep enough distance from one another to be able to distinguish one another. “We mark them with colored plastic rings on the forearms,” ​​says Dr. Knörnschild. “We can also use a directional microphone and record the sounds of individual bats.”

This is important because these bats are the only mammals other than humans known to babble like human babies. The bat pups chatter includes full-blown syllables and sounds that only the young make, and the type of chatter changes over time as the bats learn territorial and courting songs. In addition, their songs are not sung at the high frequencies that bats use for echolocation.

“It immediately reminds you of toddlers,” said Ahana A. Fernandez, also at the museum, who recently worked with Dr. Knörnschild and other colleagues carried out an analysis of the babble. Dr. Fernandez said the babbling behavior was known but not thoroughly investigated. The researchers wanted to “analyze the babbling behavior of the puppies in detail and compare it with the babbling of a human infant”.

They analyzed records of 216 “babble fights” by 20 bat pups from two colonies in Costa Rica and Panama, which lasted about seven minutes on average, but lasted up to 43 minutes. The researchers found that the puppies’ sounds resembled those of human infants in their syllable repetition, the rhythmic nature of the chatter, and the universality of chatter behavior.

As with human babies, all the pups babbled. Other similarities to the chatter of human infants included the early onset of the chatter, the long sequences of sounds, and the fact that the pups did not need stimulus from other bats. Like babies, they just kept chatting, gradually picking up more sounds. The researchers published their results on Thursday in the journal Science.

D. Kimbrough Oller of the University of Memphis, who has studied the voice development of human infants for decades, said: “There are some remarkable parallels” to the human chatter and also to the birdsong in the extensive observations and analyzes of the bat pups, one of which it was only ” the amount of chatter that’s going on ”.

Like human babies, they made noise all the time.

“Whenever you’re awake, do it,” said Dr. Oller, who was not involved in this research but will work with some of the authors on future work. He said that the bats chatter whether there is stimulation or not, like human infants do. Human babies seem to be exploring the sounds they make, he said, and playing with them as if they were hearing objects, similar to the physical objects they manipulate, taste, and play with. “I think the larger sac-winged bat probably does the same thing. I think they are probably exploring these sounds, ”said Dr. Oller.

No other mammal is known to work this type of chatter, although it is common in songbirds.

In bats, both male and female pups chatter, but females stop stringing learned syllables when they are weaned. Dr. Knörnschild said that adult women “don’t sing. They don’t produce a territorial or courtship song, and the males do. “

Then why babble? Dr. Fernandez said it could be that when the females learn what goes into a courtship song, they can better judge them when it comes to male singing. This is just a hypothesis, but the females certainly judge male songs. Males compete intensely with their bat song to attract a harem of females. The females choose which male they prefer and the males court them all the time, in a sort of constant talent competition.

“Female choice seems to play an extraordinarily large role” in mating behavior, said Dr. Knörnschild. “The males are slightly smaller than the females and cannot physically force them to do anything.”

And the females may not be looking for just the brightest or most energetic singers, according to Richard Prum, an ornithologist at Yale. In his book “The Evolution of Beauty” he argued that female birds and the females of some other animals, whether it be plumage or dancing behavior or song, make decisions based on what they like based on essentially aesthetic criteria. He said that in the case of the bats, aesthetic choice could drive the development of the song.

Dr. Knörnschild said aesthetic choice was certainly an option, although she said there were acoustic qualities in bat singing that indicated the fitness of the males.

She also suspects that there are more chattering species. Until now, the science of vocal learning has focused on birds, but in mammals mole rats, giant otters, dolphins and other whales are good targets for research.

“It would be really interesting to have more chattering descriptions of different species and then maybe determine the evolutionary pressures that caused the chatter to appear in one species and not another,” she said.