No one would be shocked to find play behavior in a mammal species. Humans love to play — as do our cats and dogs. It’s not such a leap to believe that, say, a red kangaroo would engage in mock fights. But somehow that behavior seems unlikely in animals other than mammals.
It shouldn’t, though. Researchers have documented play behavior in an astonishing range of animals, from insects to birds to mammals. The purpose of such activities isn’t always clear — and not all scientists are convinced that play even exists — but play may help creatures establish social bonds or learn new skills. Here are five non-mammals you may be surprised to find hard at play:
Alligators and crocodiles might seem more interested in lurking near the water and chomping on their latest meal, but these frightening reptiles engage in play, Vladimir Dinets of the University of Tennessee in Knoxville reports in the February Animal Behavior and Cognition. Dinets combined 3,000 hours of observations of wild and captive crocodilians with published reports and information gathered from other people who work with the animals. He found examples of all three types of play:
Locomotor play: This is movement without any apparent reason or stimulus. Young, captive American alligators, for instance, have been spotted sliding down slopes of water over and over. And a 2.5-meter-long crocodile was seen surfing the waves near a beach in Australia.
Object play: Animals like toys, too. A Cuban crocodile at a Miami zoo picked up and pushed around flowers floating in its pool for several days of observation. And like a cat playing with a mouse, a Nile crocodile was photographed as it repeatedly threw a dead hippo into the air. Object play is recognized as so important to crocodilian life “that many zoo caretakers now provide various objects as toys for crocodilians as part of habitat enrichment programs,” Dinets notes.
Social play: Juvenile black caimans in Brazil were seen chasing each other in circles. And Dinets caught two Cuban crocs “courting” each other — the male would let the smaller female climb onto him and he’d give her rides around their pool.
Subscribe to Science News
Get great science journalism, from the most trusted source, delivered to your doorstep.
“Even though these observations of apparent play behavior are mostly singular and, if taken separately, allow for alternative explanations,” Dinets writes, “combined they present strong evidence that play might be a more regular part of crocodilian behavioral repertoire than currently recognized.”
Dinets’ colleague Gordon Burghardt established five criteria that have to be met before a scientist can say that an animal is actually playing. For instance, the activity has to be spontaneous and exaggerated, and it is initiated when the animals are healthy and free of stress. And Burghardt has observed play in a variety of animals, including a Nile soft-shelled turtle named “Pigface,” who lived at the National Zoo in Washington, D.C. Pigface, who was more than 50 years old at the time, was given a basketball by his keepers. As the turtle swam around the enclosure, he batted the ball in front of him. “If you saw a dog or an otter going around batting a ball, bouncing around and chasing it, and going back and forth and doing it over and over again, we’d have no problem calling it play,” Burghardt noted in The Scientistin 2010.
The owner of this red devil cichlid, named Rooney, spotted the fish batting around a tiny ball in its tank. If the behavior meets certain criteria, scientists might classify it as play. Credit: Michelle Coyne/YouTube
Burghart and Dinets have also found evidence of play among fish. Three male cichlid fish repeatedly attacked and deflected a thermometer in their tank. Each time a fish struck the thermometer, it moved then fell back into place. The behavior was slightly different in each fish, and the fish bumped the thermometer whether or not there was food or other fish around. This “fit the criteria for play behavior,” the researchers, along with James Murphy of the National Zoo, reported in the January issue of Ethology.
Even insects can have complex social lives, and this can include play, researchers have found. Paper wasps form colonies in the spring, and when that occurs, the prospective queen wasps have to establish a hierarchy. “The dominant female wasp approaches the subordinate, raising her head over the subordinate’shead, performing a rapid beating of the antennae, and often licking, biting, and asking for food,” Leonardo Dapporto of the University of Pisa in Italy and colleagues described in a 2006 paper in the Journal of Comparative Psychology. But spring isn’t the first time the wannabe queens wasp exhibit such behaviors. Researchers have found that those wasps display most of those same behaviors about six months earlier. At that time, the behaviors don’t matter; they have nothing to do with establishing a hierarchy. But those behaviors do look a lot like the play fighting seen among mammal species, the researchers say.
Michael Kuba of the Institute for Evolution and Cognition Research in Altenberg, Austria, and colleagues found evidence of play in octopuses when they gave objects made of Lego blocks to 7 adult and 7 sub-adult animals held in the lab. Nine of the cephalopods exhibited playlike behavior, pushing or pulling the objects or floating them on the surface. One octopus knocked the Lego objects around so much that the researchers classified his behavior as full-fledged play in their 2006 Journal of Comparative Psychology paper. More recently, Jennifer Mather of the University of Lethbridge in Canada has caught octopuses at the Seattle Aquarium blowing streams of water at empty pill bottles. The action, which causes the bottles to shoot away, qualifies as play, Mather says, because the octopuses did it not one or twice, but 20 times over.