This story appears in the October 2016 issue of National Geographic magazine.
Nicolas Mathevon Biologist
Nicolas Mathevon knows what boils a crocodile’s blood. In Guyana in 2007, when Mathevon played a recording of an infant croc distress call, a bellowing mama croc lunged at the boat he was in. He switched off the speaker, and the animal halted mid-attack. After 10 years of studying crocs’ communication methods, in Venezuela and elsewhere, Mathevon says he’s seen mothers react quickly to babies’ signals but still know when to “spare their energy.”
In translating croc chatter, Mathevon, a professor of animal behavior at the University of Lyon at St.-Étienne in France, found that the cold-blooded creatures are actually loving mothers. When babies in the egg are ready to hatch, they signal each other and their mother with an umph, umph, umph call. When Mathevon recorded that sound and played it back to mothers via loudspeaker, they rushed to their nests to dig out their eggs. If the recording played next to eggs, the babies—likely believing their neighboring siblings were signaling having reached full term—responded by hatching. Mathevon also discovered that after they’ve hatched, baby crocs can make a sound that sends their mother running to them, and he observed that Mom makes a certain call when she wants them to congregate around her. “They have a very developed social life,” says Mathevon. “They’re a model of interaction between mother and newborns.”
As babies grow, Mathevon says, their acoustics change and their maternal relationships become more fraught. The mothers that were once so attentive no longer come running. He theorizes that they may even be “a little bit frightened” by offspring’s calls.