Crocodiles, just like humans, think surfing waves, playing ball and going on piggyback rides are fun, a new study suggests.
Vladimir Dinets, a research assistant professor in psychology at the University of Tennessee, Knoxville, has observed crocodiles engaging in play-like behaviour.
He has conducted an informal survey of crocodilian-themed groups on social media and various conferences.
Previous research by Dinets discovered that crocodiles are able to climb trees, work as a team and use lures such as sticks to hunt prey.
The new research shows that crocodilians engage in all three main types of play distinguished by behaviour specialists: locomotor play, play with objects and social play.
Play with objects is reported most often. Crocodilians have been spotted playing with wooden balls, noisy ceramic bits, streams of water, their prey and debris floating in the water.
Cases of locomotor play include young alligators repeatedly sliding down slopes, crocodiles surfing ocean waves and caimans riding currents of water in their pools.
Observed cases of social play include baby alligators riding on their older friends' backs, baby caimans playfully "courting" each other and a male crocodile giving his lifetime mate rides on his back.
Crocodiles have also been seen playing with other animals. Dinets observed a juvenile alligator playing with a river otter.
In rare cases, individual crocodilians have been known to bond so strongly with people that they become playmates for years. For example, a man who rescued a crocodile that had been shot in the head became close friends with the animal.
They happily played every day until the crocodile's death 20 years later. "The croc would swim with his human friend, try to startle him by suddenly pretending to attack him or by sneaking up on him from behind, and accept being caressed, hugged, rotated in the water and kissed on the snout," said Dinets.
Dinets' work provides further evidence that play is a universal feature of "intelligent" animals - those with complex, flexible behaviour. This knowledge might help determine how intelligence evolves and what is needed for its development.
The study is published in the journal Animal Behavior and Cognition.