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September 2002



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Meerkats Stand Tall








By Tim Clutton-Brock
In the slanting, golden light of a Kalahari evening, Juma, a young male meerkat, stares across the sandy bed of the Nossob River: nothing but the shimmer of hot air and the evening chorus of barking geckos. Six pups, their eyes only recently open, nuzzle at his stomach, hoping to find milk. Juma has been watching over them since dawn, ignoring his own hunger as he scans the sky for eagles and the ridgeline for jackals, snakes, yellow mongooses, and even neighboring meerkats, which would kill the pups if they found their burrow unguarded.
 
In a large meerkat group, which can have as many as 40 members, six-month-old Juma would be too young to baby-sit. But there are only five adults in his small group, so he must take his turn guarding the pups. Of the ten meerkat groups that my research team—biologists from the University of Cambridge and the University of Pretoria as well as a few students—followed during five years in what is now called Kgalagadi Transfrontier Park, we came to know Juma and his family best. We nicknamed them the Jackson Five, in honor of Tim Jackson, a resident biologist who discovered the group when it had only five members, and they quickly became accustomed to our presence, allowing us to follow them around their six-square-mile  (15.5 square-kilometer) range.
 
Meerkats make ideal study subjects because they are only active during the day. Also, perhaps because they are prey to a large variety of birds and mammals—over half the adult meerkats in our population were killed each year—they quickly learn to recognize danger and to ignore animals that do not pose a threat. Humans, with time and patience, generally fall in the latter category, and meerkats come to accept them completely.
 
As we sat beside their burrows in the cold Kalahari mornings, the meerkats sheltered behind us from the keen dawn wind. When no stumps were close by, tamer individuals would sometimes climb up our backs and take their turns as sentinels from our shoulders or heads. The more they trusted us, the closer we were able to get. We collected skin and hair samples for genetic analysis, spooned up their droppings to measure their levels of sex hormones, and, using crumbs of hard-boiled egg as an incentive, trained them to climb onto electronic scales.
 
This long-term study, from 1993 to 1998, grew out of my belief that meerkats might offer vital insights into the evolution of mammalian cooperation. According to evolutionary logic, an individual's success is usually measured by the number of offspring it raises, but some meerkats spend part or all of their lives helping others raise young rather than breeding themselves. Such seemingly altruistic behavior can be found in very few mammals, but even within this select group, which includes mole rats, marmosets, wild dogs, and some other mongooses, meerkats are unique in the extent and coordination of their cooperative activities.
 
Meerkats' unusual system of rearing their young poses questions that go to the roots of our understanding of cooperative societies, including our own. Why do mature offspring remain in their parents' group instead of dispersing to breed? Why do they take risks and spend time and effort to help other members breed? How do group members divide their responsibilities and coordinate their contributions? And how do they ensure that all group members pull their weight?
 
Few of our closest relatives, the great apes, cooperate with each other as extensively as meerkats. Human cooperation probably has an ancient history, and by studying meerkats, which depend on their group for survival, we gain a window into the evolution of cooperative societies.
 
Our research on these issues progressed steadily until, two years into the study, disaster struck. The irregular rainfall of the Kalahari failed completely, and the remaining grasses in the park shriveled and died. Twisters cruised up and down the riverbed, and the springbok and wildebeests left to search for the last remnants of grass in the dunes. At first the meerkats hung on, digging for beetles and scorpions in the loose sand, but gradually their condition deteriorated and they were forced to forage farther and farther from bolt-holes— quick-escape burrows scattered throughout their range—and spend more and more of their time without the protection of sentinels.
 
Predators quickly took their toll: The Jacksons' dominant female was the first to be killed, followed rapidly by the dominant male and by Juma's older sister—all three probably taken by one of the martial eagles that rode the morning thermals over the riverbed.
 
Eventually Juma was left alone with three younger sisters. For the next year these four were inseparable, a cautious group whose seamless alternation of sentinel duty ensured that no predators could get close to them. Other groups fared worse: Six of the ten groups that we had habituated were wiped out, leaving vacant ranges.
 
The rains returned the next spring, and the remaining groups started to breed—except for the Jacksons, all of whom were close relatives. At last, in midsummer, an unrelated male immigrated into the group, and, soon after, Juma left his sisters and his range for the first time in his life. We combed the riverbed, fearing he'd been killed, but found him two months later in a vacant range with two adult females and a related subadult male from a neighboring group.
 
Over the following months Juma filled out. His temporal muscles enlarged, giving him extra biting power. He put on weight and assumed the rolling gait and swagger of a dominant male. He quickly set about breeding with one of his new females, and they raised four pups successfully. Gradually the size of his group grew—from four to eight to fourteen to twenty.
 
Living in tents and caravansin our Nossob River campsite 30 miles (48.2 kilometers) north of Juma's range, my team and I monitored the lives of more than 200 meerkats during our five years in the park. Our immersion in the meerkats' world helped us unravel many mysteries about them, and, in turn, gave us clues to the behavior of other types of cooperative mammals. But we still struggled with one question: Why did subordinates go to such elaborate lengths to help raise others' young?
 
Biologists first pointed out in the 1960s that individuals that do not themselves breed can propagate their genes by helping relatives breed. An interest in advancing their relatives' survival, however, cannot be the whole story. In meerkats, as in many other cooperative breeders, all group members willingly help rear young, whether they are related to them or not.
 
The answer, at least for meerkats, is interdependence. Everyone benefits from living in a larger group, and everyone suffers when group size falls. No one individual can afford to spend more than an hour or two on guard each day, so small groups spend part of their time without sentinels. The larger the group, the more individuals there are to feed the pups, who grow faster and are more likely to survive. (Even nonbreeding females will lactate at the same time as breeding females.) Bigger groups are also better able to repel neighbors' attempts to take over their ranges.
 
Juma certainly benefited from the large size of his group. His weight increased, and he fathered six litters. Then disaster struck again. His dominant female suddenly disappeared, probably killed by an eagle or a jackal, leaving him with four mature daughters—but no female to mate with. Another group with adult females lived just south of Juma's group, and a large group with several roving males lived to the north. Juma persistently tried to lead his group south to the females, but his daughters dragged their feet and headed north toward the males whenever they got the chance. Pulled by conflicting desires, the group moved up and down the riverbed.
 
By this time we had our own problems. We had been working in the park for five years, and the authorities thought this should be long enough to complete the study. Eventually we were forced to pack up camp and leave.
 
We had followed Juma since he was a juvenile, and losing contact with him was like losing an old friend. Luckily, we had been habituating meerkats at a second study area 60 miles (96.6 kilometers) to the southeast on the Kuruman River. The work had been slow, but by the time we left the park we were able to observe eight groups at Kuruman, and we could recognize each individual. We simply shifted our camp and pursued our research with different individuals.
 
The past few years have brought good rains, and many of our Kuruman groups are now 30 animals strong. There are more group members to share the task of guarding and feeding young, so each individual expends much less time and energy on cooperative activities. It's a far cry from the groups of four or five that we watched struggling to feed their pups in the park.
 
And juma? last year my south African colleague Justin O'Riain and I were allowed to spend a week in Kgalagadi to check on the survival of the individuals we had last followed in 1998. The population had not yet recovered from the drought of 1995, and many of the ranges were still empty. The Jacksons were no more—one of their main burrows had been taken over by a family of bat-eared foxes, and the other was clogged with loose sand.

We searched for two days in the area where Juma and his family were last seen, scouring the sides of the riverbed with binoculars, but with no luck.
 
Finally, on our last evening in the park, we saw six meerkats standing near one of Juma's old burrows. We walked slowly over to them. Five stared, barked at us, and disappeared into the burrow. One male remained, rocking from side to side, seemingly unsure whether he should follow his companions or stay behind. We sat down ten feet away. He watched as we unpacked the scales, filled the weighing tray with sand, and topped it with hard-boiled egg, just as we had once done each day. He approached hesitantly, gaining confidence with each step. A dark mark below his right eye, which in the past had always distinguished Juma from the others, was still obvious. We had found him.
 
Juma carefully climbed onto the scale, and we weighed him. At 28 ounces (793.8 grams) he was lighter than he had been at his peak, but he was still the dominant male of his group. He and one other male were the only survivors of the animals that we had left in the park. He was eight years old, the oldest dominant male we have known, and unlikely to live much longer. But his group was one of the largest in the area and will probably maintain its range. Eventually it will produce splinter groups, and a new generation of meerkats will fight for survival in the vast sand sea of the Kalahari.

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