Nile crocodiles react rapidly to the cries of a baby if it sounds distressed
Blickwinkel/Alamy
Crocodiles possess a remarkable ability to perceive and respond to the distress cries of human infants, as well as the young of other great apes. In fact, they may even be better at recognizing distress than humans are, according to Nicolas Grimault at the University of Lyon in France.
Unlike humans, crocodiles rely on changes in frequency rather than pitch when it comes to detecting distress in infant cries. When they hear the sounds of distressed human, chimpanzee, or bonobo infants, crocodiles quickly move towards the source. While some crocodiles may perceive the infants as potential prey, others might display protective behavior towards them.
To study the responses of crocodiles, Grimault and his colleagues conducted experiments using recorded cries of 24 hominid infants. This included 12 human infants, six captive bonobos, and six wild chimpanzees. The cries were recorded during varying levels of distress, such as conflicts with other apes or separation from their mothers.
The researchers played these recordings near groups of male and female Nile crocodiles at the Crocoparc zoo in Morocco. The crocodiles responded by turning their heads, swimming towards the sound, and even biting the speakers playing the cries.
Grimault notes that crocodiles are usually immobile animals, so their strong reaction to the baby cries is quite significant.
The crocodiles’ reactions were more pronounced when the cries had non-linear acoustic characteristics, such as vocal roughness, frequency jumps, or subharmonics. These features are associated with higher emotional arousal. In contrast, humans tend to assess distress levels based on pitch, which crocodiles appear to ignore. This suggests that crocodiles are less likely to confuse the distress levels of species with naturally higher-pitched cries, such as bonobos.
The findings indicate that crocodiles, which thrived in the African cradle where human evolution took place, could have posed a significant danger to early human settlements. While most crocodiles reacted in a predatory manner to the cries, there was one individual that displayed protective behavior. It is believed to be a female crocodile defending the speaker from other crocodiles, similar to how female crocodiles protect their young from cannibalistic males.
Grimault mentions that the attractiveness of babies’ cries to crocodiles has been known for a long time. European hunters in Sri Lanka reportedly used crying human babies to lure crocodiles into shooting range during the 19th century.
