A new study has found that Nile crocodiles respond to the crying sounds of chimpanzee and bonobo babies, as well as human babies. What’s more, crocodiles seem to respond best to higher-intensity cries – and perhaps better than humans at perceiving the level of distress in those cries.

It is not clear from the study whether this behavior is caused by crocodiles trying to prey on vulnerable prey or for some other reason, such as confusing the cries of these babies with those of young crocodiles, which can make a sound, such as squeaking or barking, for example. . But these results give researchers more insight into how these giant reptiles perceive the world.

By playing a group of Nile crocodiles (Crocodylus niloticus) at the zoo to the cries of human babies, chimpanzees and bonobos, the researchers recorded how many crocodiles turned their heads or moved towards the loudspeaker in response to the sounds. They published their results in a journal Proceedings of the Royal Society B.

Crocodiles responded to the cries of human babies, bonobos, and chimpanzees. But not all screams sounded the same.

The researchers used audio recordings of human infants in two contexts: at home bathing with their parents, which caused low-intensity crying, and in a doctor’s office, during vaccinations that caused higher-intensity crying.

Some of the more intense cries of children caught the attention of a larger percentage of crocodiles. The researchers also analyzed some of the acoustic properties of the screams they tested to test whether these sounds had certain qualities that cheer the crocodiles.

The authors discovered that crocodiles responded better to cries with more energy at higher audio frequencies and to cries with some degradation in sound wave structure, both of which were associated with higher levels of distress.

“Imagine a baby crying very sad — when the baby screams and loses her breath, the crying sound is erratic and ubiquitous,” said Miriam Boucher, a doctoral student at Clemson University who was not involved in the new study.

The study’s authors note that people tend to rate loud calls as more annoying, but this doesn’t always give an accurate assessment. For example, because bonobos’ cries are louder than humans’, people tend to exaggerate them as frightening. The crocodiles, on the other hand, did not seem to react so differently to screams of varying intensity.

“Therefore, crocodiles appear particularly well adapted for assessing the degree of distress encoded in an infant’s cry, regardless of hominid species,” the authors write.

“It’s possible that these animals took distress as a signal to detect potential food nearby, and some crocodiles respond to calls by swimming underwater, which could be a predatory maneuver,” Boucher said. .” Said.

Crocodiles may also have responded to these calls for a reason other than hunting. The study did not compare the crocodile’s response to these calls with another type of sound, such as a young crocodile’s distress call or a neutral sound. Kent Vleet, a retired University of Florida biologist who was not involved in the new study, said he has seen alligators (a group of animals that include alligators, crocodiles and caimans) respond intensely to children’s danger signals, even when they are present. from other crocodile species.

Additionally, these animals may be interested in a new sound nearby.

“What I’ve seen in my own study,” Boucher said, “is that crocodiles can be pretty curious about things in general.”