Nile Crocodile(Crocodylus niloticus) swimming (Photo by By MathKnight and Zachi Evenor – Own work, CC BY 4.0, https://commons.wikimedia.org/w/index.php?curid=36133676)

Dear Readers, while ‘crocodile tears’ are usually thought to be false tears, emitted without any actual emotion, it turns out that the Nile Crocodile, which can grow to a maximum of 20 feet long, is highly attracted to the cries of primate infants, including humans. It is even better at detecting distress than humans are, which is quite something.

You might think that the sound of an infant in pain or under stress might be appealing to a crocodilian because it indicates an easy meal, and largely you would be right. Scientist Nicolas Grimault, of the University of Lyon, played the distress calls of young bonobos (in European zoos) and wild young chimpanzees from Uganda to a group of 25 captive Nile Crocodiles. The calls of the bonobos and chimpanzees were recorded in a variety of circumstances, mainly when there was conflict within the group, or the babies found themselves some distance from their mothers. Grimault also played the cries of human babies, varying from low-level distress at bathtime to more anguished sounds from visits to the doctor for vaccinations.

The sounds were played to the crocodiles after the park where they lived had closed – each call lasted 30 seconds, with at least ten minutes between each recording

On hearing the calls, many of the crocodiles turned their heads and swam towards the sound, sometimes even biting the speakers. As crocodiles are usually such immobile animals this was a very strong reaction. The strongest reactions seemed to come when it sounded as if the call was outside the normal vocal range of the animal that made it, so the crocodiles were reacting to the degree of distress. Humans seem to react to the pitch of a call – the higher the pitch, the more urgent the call seems to be – which means we aren’t as good at gauging the distress of non-human primates as a crocodile is – they seem to know when a bonobo call is outside its normal range, whereas we don’t account for the normal higher pitch of their ‘voice’. A crocodile can listen to a cry of anguish and make up its mind in an instant whether there’s a potential meal or not.

But wait! One female crocodile didn’t seem to be quite so food-orientated as the others. When she heard the distress calls, she positioned her body between the speaker and other crocodiles – male crocodiles are cannibalistic on baby crocodiles, and female crocodiles often have to put themselves between their babies and adult crocodiles. Baby crocodiles also have very high-pitched calls, so perhaps the sounds are a trigger, regardless of species.

Interestingly, Grimault suggests that there is evidence of crying babies being used to lure crocodiles into shooting range in Sri Lanka during the colonial era of the 19th Century, so although not studied scientifically before, the way that crocodiles react to the distress cries of primates seems to have been known for a very long time.

You can read the whole article here.