Featured Story
April 2007
Meerkats At Play
Evolution demands that activities costing a lot of energy provide survival value in return.
But what do these rambunctious little mammals gain from having so much fun?
By Lynda L. Sharpe ~ Photographs by Andrew J. Young
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The two young meerkats were acting out one of the greatest mysteries in the world of animal behavior. They were playing. And those of us who study that behavior have no idea why.
Unlike virtually every other kind of animal behavior, play seems to serve no purpose. It is easy to see what an individual gains from grooming, or fighting, or nest building. But play? And if play really has no purpose, why do young mammals (including humans) invest so much time and energy in it?
I kept watching as Imp chased Bandit beneath a spiky shrub. The pair darted back and forth, leaping exuberantly as they snapped and parried. It was clear that they were having a high old time. After all, play is fun; it gives pleasure. Isn’t that reason enough to do it? The trouble with such reasoning is that play can also have harmful consequences, which could reduce an individual’s chances of surviving to reproduce. Unless play provides some compensatory benefits, evolution would have eliminated the tendency to play. So what benefits do individuals get from playing? My own behavior—crouching in the Kalahari Desert of southern Africa surrounded by eighteen meerkats—was part of an attempt to answer that question.
The meerkat, a species of mongoose, is one of the most sociable mammals in nature. The animals live in highly cooperative groups of as many as fifty individuals. Group members all chip in to rear the young and guard against predators. As I watched “my” group—which had been named Elveera, after the founding individual—a pair of adolescents groomed the ticks from each other’s noses, while the alpha female, Tenuvial, presented a wormlike larva to one of the pups. I could see how meerkats had earned a reputation for altruism and an “all-for-one-and-one-for-all” approach to life.
The Elveera group was one of thirteen such groups being studied by the Kalahari Meerkat Project, established in 1993 by Tim Clutton-Brock, a behavioral ecologist at the University of Cambridge. Thanks to several years of work by Clutton-Brock’s research team (which I joined in 1996), these wild animals had become used to having a person in their midst, and so I could sit among them without disturbing their behavior. To them, I was a harmless prop in the scene. As if to prove the point, Bettik (Imp’s mother) trotted over and scrambled awkwardly up my arm, her long claws scratching my skin. Using me as a shrub or a stump, she perched precariously on my shoulder to scan the sky for predators, so the rest of the group could nap in safety.
Suddenly Bettik whistled a piercing alarm, startling the other meerkats—and me. She leapt from my shoulder and dashed with the others to the entrance of the group’s burrow. Little Bandit and Imp, however, playing at the foot of the dune slope, had a long way to run. High above, circling in the pale morning sky, a tawny eagle was on the lookout for just such incautious meerkat pups, a perfect example of the potential cost of play. This time, however, Bandit and Imp shot down the burrow, emerging moments later to peep out cautiously from between the forelegs of their elder brother.
Although young meerkats clearly risk predation or injury during play, they incur an even more substantial cost in energy. Our research in the Kalahari has shown that meerkat pups that are bigger than their siblings grow into more efficient foragers, and they are more likely to become dominant within a group and to breed.
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The failure of science to determine the function of play has not been for lack of trying. Investigators, particularly in the 1970s and 1980s, have conducted studies across a range of animal species. People assumed that once accurate information was gathered about the mechanics of play, its function would become self-evident. After all, that approach had worked with almost every other behavior observed in animals. But it did not work for play.
What we do know is that the “content” of a youngster’s play reflects what is important to adults of the same species: lion cubs stalk and pounce; antelope fawns gallop and pronk. We also know that play is stimulated by novel objects, novel partners, and novel substrates, such as mud or snow. And of course theorists have come up with many hypotheses, suggesting more than thirty possible benefits of play.
For example, play may stimulate the development of the brain, increase cardiovascular fitness, or help regulate the use of energy. Perhaps play in young animals is a way to practice skills they will need in adulthood, such as fighting, mating, or hunting. Perhaps it is an effective way to learn how to recognize kin, evaluate risk, or cope with stressful situations. The pleasure of play might provide the positive reinforcement needed to strengthen social bonds between individuals, thereby reducing aggression, enhancing alliances, and improving group cohesion. Unfortunately, none of those theories has been rigorously tested, and there is little evidence to support or refute any of them.
The sun was now well above the horizon, and the meerkats were wide-awake. The entire group began to play vigorously. As a knot of five pups twisted and rolled over my feet, I knew that there could be no crucial, controlled experiment; there was no way I could prevent a meerkat from playing just to see what happened. Even among captive animals, investigators have found it impossible to stop young mammals from playing without so disrupting their lives that any subsequent changes in their behavior are uninterpretable. How, then, could I test theories about play?
Some theories simply do not lend themselves to testing in the field. But for assessing the possible social benefits of play, wild meerkats seem ideal subjects. You see, though meerkats are highly social, they belong to a family known as the Viverridae in which almost all the species are solitary. As the African climate dried out and the forest turned into savanna, the ancestral mongooses, which foraged out in the open by day, became extremely vulnerable to predation. By sticking together and sharing guard duty, mongooses could substantially reduce their risk. In fact, our observations show that large group size in meerkats is associated with higher rates of growth, survival, and fecundity.
Yet before mongooses could take advantage of the benefits of group living, they had to overcome their inherited antipathy toward other members of their own species. So could play be the key? If play could enhance the bonds between individuals, reducing their aggression and encouraging them to stick together, its evolutionary benefits would be unmistakable. And observers would see meerkats fully exploiting play for just that purpose.
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To determine whether meerkats at play were strengthening their social bonds, I had to find out how much each individual played, then look at how differences in the frequency of play affected each animal’s behavior. If the social-bonding hypothesis was correct, I reasoned, meerkats that play a lot should be more strongly attached to their fellows than meerkats that play rarely. “Bonded” animals, moreover, should be less aggressive and more strongly committed to the group: they should help more often with group activities and delay their own departure from the group as young adults.
I decided to focus on eight meerkat litters, each from a different group—forty-five pups in all—and then follow them throughout their lives. Recording how much the meerkats played proved harder than I had expected. On some days the entire group would play for more than an hour—as was happening this morning at Elveera. On other days, there was no play at all. Also, it was a year of good rains in the Kalahari, so a sea of golden devil thorn flowers made it hard to spot the meerkats as they dove in and out among the blossoms. Worst of all, meerkat play moves so fast that it was almost impossible to see the identifying marks I’d made by trimming small patches of fur or painting dabs of black hair dye on my subjects’ bodies. The only body parts that reliably protruded from a scrum of wrestling meerkats were the tails. So each morning, before collecting data, I had to crawl around on my stomach amid the sunning meerkats, clutching an array of multihued marker pens, and surreptitiously draw vibrant rings on the tails of all my study animals.
In spite of the difficulties, I managed to quantify how much each animal played, and found that individual differences were quite large. In the Elveera litter of nine pups, one large, blonde pup called Mimi played twice as often as Bandit or a shy pup named Elf. So one of my questions became, simply: was Mimi less aggressive than Bandit or Elf?
As it happened, there was a good way to quantify aggressive behavior to help answer this question. From four to ten weeks of age, when meerkats learn to find food on their own, each pup must compete for prey items donated by older members of the group. The adults tend to feed whichever pup is closest by, so whenever the group goes foraging, the youngsters fight each other ferociously to get the closest possible position to one or more of the group’s most generous feeders. By following each pup in turn, and recording what happened whenever another pup came within a meter of my focal pup, I found I could determine which individuals were most inclined to act aggressively.
Close to my feet, Imp, the smallest pup, was tagging along behind Tenuvial, begging lustily; making an ear-piercing racket actually encourages adults to donate prey items to the pups. Within moments, dark-eyed Bandit launched a fierce attack on Imp. The two pups hurtled toward each other, crashed together, and rolled over and over, squealing, growling, and biting mercilessly. In the end, Bandit emerged victorious to usurp Imp’s place beside Tenuvial. Fighting is common among pups of this age, but if the social-bonding theory is correct, the combatants that engage most often in such ghastly struggles would be pairs that rarely share in play. Furthermore, preferred playmates would fight with each other less frequently. So are those predictions correct?
As it turns out, they are not. There was no correlation between how much an individual (or a litter) played and how aggressively it behaved. Blonde Mimi spent twice as much time as Elf did in play, but she launched just as many attacks on her littermates as Elf did. Similarly, preferred playmates such as Bandit and Mimi were just as likely to fight while begging for food as were pups such as Bandit and Elf that rarely shared in play.
Play also had no short-term effect on aggression. Pairs of pups out foraging were just as likely to attack each other within ten minutes of playing together as were pairs of pups that had not just played. And female meerkats that played relatively often with the group’s alpha female were just as likely to be bullied and harassed by her (when she was feeling aggressive during late pregnancy) as were females that had not played with the alpha.
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Social-bonding theory does not just predict that play reduces aggression; it also maintains that play strengthens an individual’s attachment to its playmates, promoting alliances and enhancing group cohesion. Did meerkats that played more often—Mimi and a pinch-faced meerkat named Goblin—subsequently show greater commitment to their group? And did pairs that liked to play together team up later to form special alliances in adulthood?
To begin answering those questions, I recorded how much each of my meerkats contributed to the activities of its group. My working assumption was that the more closely an individual was bonded to its group, the more it would want to contribute to the group. Furthermore, I reasoned, the more closely bonded an individual, the longer it would remain with the group and so the more it stood to gain from its contributions to group well-being.
Fortunately, it was fairly straightforward to collect data on group contributions. By the time my study animals were three or four months old, they were already dashing about excitedly, helping rear the next generation of pups. I recorded how often each animal donated prey items to the new pups, and on how many days it babysat. Babysitting seemed particularly altruistic: the babysitter had to go without food for the day in order to remain at the breeding burrow with the newborn pups, while the rest of the group went foraging. I also measured how often each meerkat performed sentinel duty, and how often it helped clear debris from the group’s sleeping burrows and bolt-holes.
Collecting data on alliances was also relatively straightforward. Meerkats usually remain with their natal group until they are about two years old (de-spite reaching sexual maturity between seven and eleven months). When the meerkats finally left their natal group, I could note which ones left earliest (the behavior expected of poorly bonded individuals) and which ones formed so-called dispersal alliances (that is, left their natal group together).
So did play strengthen a meerkat’s commitment to its group, enhancing group cohesion? No. Mimi, Goblin, and other pups dedicated to play did not end up contributing more to the group than meerkats that played infrequently. In fact, within the Elveera group, Bandit became the most dedicated babysitter despite his relative lack of play. Similarly, individuals that played more frequently than their peers did not delay leaving their group. The highly playful Goblin left home to join a neighboring group when he was only eleven months old. Bandit, by contrast, stayed in the Elveera group until he was three. Among the females, Mimi, Imp, and two of their sisters left home at twenty months of age to set up their own group with males from another group. In contrast, Elf (the nonplayer) remained behind in Elveera.
What about the role of play in helping individuals establish lifelong alliances, such as dispersal partnerships? Meerkats typically disperse with one or more groupmates of the same sex. Furthermore, dispersing animals in large parties are less stressed, better fed, and more likely to oust competitors than animals that disperse alone or in pairs. Could that be the purpose of meerkat play, to cultivate bonds between potential dispersal partners?
Once again, on scrutiny, the supposed connection disappears. Meerkats that played together most often did not appear to be more closely attached. Frequent playmates did not groom each other any more often than they groomed other group members, and they were just as likely to engage in teenage squabbles over status. Male meerkats were no more likely to team up with their preferred playmates when embarking on short-term forays to neighboring groups to check out the “talent.” And as for dispersing, the individuals with which my study animals dispersed were not the ones they had played with most often.
In short, despite all my efforts, I did not find out why meerkats play. What I did show, at least, is that they do not play to strengthen social bonds. And if meerkats aren’t using play in that way, it’s almost certainly because play is simply not capable of generating the physiological changes needed to reduce aggression or increase social attachment.
Back in the Elveera group, the meerkats finally stopped foraging and withdrew into the tangled shade of a fallen camel thorn tree for their midday siesta. While the adults sprawled on their tummies, legs splayed out to make more contact with the shade-cooled sand, I let myself relax and enjoy the company of my study animals. In the long strip of shade beneath the fallen trunk, the nine pups lay side by side in a neat line. Too tired for their usual exuberant play, they lay on their backs, waving their stumpy legs in the air, and lazily gnawed on their neighbor’s ears, nose, and toes. I smiled at their mystery.
Originally from Australia, Lynda L. Sharpe joined the Kalahari Meerkat Project of the University of Cambridge in 1996. She spent eight years in the desert in South Africa studying the social behavior of meerkats, earning a doctorate from the University of Stellenbosch in South Africa. Flower, one of the pups Sharpe followed from birth to adulthood, is the dominant female of the Whiskers meerkat group, now starring in the Animal Planet television series Meerkat Manor. Before her work with meerkats, Sharpe was at Monash University in Australia, where she studied play behavior in the puppies of captive African wild dogs and in carnivorous marsupials. She is doing postdoctoral research on sentinel behavior in dwarf mongooses at the University of Stellenbosch.
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Copyright © Natural History Magazine, Inc., 2007