Meerkat society

Meerkats (Suricata suricatta) are small, carnivorous mammals weighing on average less than one kilogram. They inhabit the arid areas of southern Africa and live in social groups of 2-50 individuals, consisting of one dominant pair and a variable number of subordinate helpers who may or may not be related to the dominant pair. These members of the mongoose family (Herpestidae) eat mainly arthropods (insects, spiders and their relatives), as well as the occasional small mammal, reptile or plant bulb.

They have territories with several sleeping burrows, from which they make daily foraging trips of up to a few kilometres. Depending on food availability and predation pressure at specific spots, they will either return to the same sleeping burrow for several nights, or change burrows quite frequently. On average, litters consist of three to four pups that stay within the burrow until they are approximately three weeks old. During that time, while the pups are being fed on milk, the group returns to the same burrow. At four weeks of age, the pups begin travelling with the group and, for the first three months of their lives, are fed on invertebrates and small vertebrates are by helpers.

Meerkats at a sleeping burrow. Sleeping burrows may have several exits and rooms inside. Meerkats maintain them but don’t dig them; instead they use ground squirrels’ burrows and sometimes also share them with yellow mongooses that live in small family groups Image courtesy of Mico Tatalovic

Meerkats reach adulthood at around one year of age. At around 18-30 months of age, males voluntarily leave the group, either to join an existing group or to form a new group with unrelated females. Adult females, particularly pregnant ones, may be evicted from their home group by the pregnant dominant female; this is thought to reduce the chance of the dominant female’s pups being eaten by the other females. Most females return to the group once the dominant female has given birth, but some may permanently disperse to form new groups with unrelated males.

Dominant meerkats live for 6-10 years on average, with the oldest individual in the Kalahari Meerkat Project being almost 13 years. The age of subordinate meerkats is more difficult to record, as many disperse or are evicted by the age of around three years, and are subsequently lost to the project records. The most important known causes of death are predation, fights with other meerkats (including infanticide), diseases and human-caused factors such as car fatalities – but for two-thirds of the Kalahari Meerkat Project meerkats, the cause of death is unknown, since the individuals just disappeared.

Meerkats are an excellent model species for studying behavioural biology and ecology because they can be habituated to close observation by humans; they are also diurnal and forage in a relatively open habitat and are hence easy to follow and observe on foot. The aspect of their lives that interests evolutionary biologists the most is their sociality. Why do they live in groups? Why do the young adults stay in the group and why do they help each other? What are the evolutionary conflicts among individuals living in groups and how are these resolved?

Benefits of group living

For meerkats, group living makes sense because there is little available land for establishing their own territories, most of the appropriate habitat having already been taken by rival groups, and the harsh desert environment makes it difficult to survive alone.

Two meerkats coming out of a sleeping burrow Image courtesy of Mico Tatalovic

All adult meerkats contribute to co-operative behaviours; the main ones are pup feeding, sentinel duty, burrow maintenance and, for females, allolactation (lactating for another meerkat’s pups). Co-operation increases the pups’ survival, development and subsequent reproductive success, which benefits the group as a whole, because larger groups are more likely to survive.

Costs of group living

There is a trade-off for individuals between the benefits and costs of group living. One of the main costs of group living is the prevention of reproduction: the dominant breeding pair accounts for around 80% of the offspring born to the group. Dominant females try to weight the reproduction in their own favour, so that they produce as many offspring as possible; subordinate females are commonly expelled from the group by the dominant female in the latter half of her pregnancy to prevent infanticide by subordinates. Subordinate females are also evolutionarily driven to reproduce, in spite of attempts by the dominant female to prevent this from happening. Similarly, subordinate males try to find receptive females from neighbouring groups and thus enhance their reproductive success.

The exact nature of these within- and between-group conflicts and resolutions is a subject of continuing research. Currently, scientists are looking at the way in which different hormones such as oxytocin (the ‘trust’ hormone) affect social behaviour and conflicts within the group. Others are examining the influence of an individual meerkat’s personality on its behaviour and decisions.

Meerkat research

The Kalahari Meerkat Project was set up some 15 years ago by Professor Clutton-Brock from the University of Cambridge, UK. Since then, the Cambridge scientists have collaborated with colleagues in other countries, especially at the University of Zurich in Switzerland and Pretoria University in South Africa.

All meerkats involved in the project are wild but habituated to people and are easily identifiable by small dye marks that the researchers and volunteers have painted on them. These dye marks make for easy identification, as ‘head and shoulders’ is different from ‘right rib, right thigh’. Familiar with people since birth, the animals ignore us so we can observe them from as little as 0.5 m away and walk among the group without disturbing their normal behaviour. Since most meerkats are studied from birth, each individual’s parentage and life history is recorded.

The project manager makes a weekly schedule of group visits to allow researchers (master’s students, PhD students and postdoctoral researchers) to visit the meerkat groups they need for their experiments and to make sure all groups are visited at least a couple of times a week by volunteers to keep track of where the animals go and what they do. In every group, one animal has a radio collar that allows it to be tracked; most of their sleeping burrows are also labelled with GPS points so it is easy to locate them. All pups are caught and an identity microchip is inserted under their skin in case the dye marks on their fur wear out. Blood samples are also taken at regular intervals throughout their lives, to obtain both their DNA and hormonal profiles. This helps researchers to determine relationships within and between the groups and to correlate behaviours with hormone levels. The animals are captured for only a few minutes, to avoid stressing them too much.

For the scientists, a typical day of meerkat research involves waking up before sunrise to arrive at the sleeping burrow before meerkats get up. Various records have to be kept, such as where the animals slept, when they got up, how heavy they are (we use small crumbs of hard-boiled egg to lure them onto scales, saying “yum, yum, yum!”). We also count and identify all the animals to check the group’s composition and then follow them for three hours while they forage for food and avoid predators. When following them, we also take regular GPS readings to calculate the routes that the meerkats take on their foraging trips. At midday, when the meerkats have a siesta to avoid the heat of the desert sun, we leave to have lunch and return in the afternoon for more data collection. Afternoon experiments might include playing the meerkats’ own vocalisations back to them or presenting them with predator cues or faeces to observe their responses.

Review

This article provides some basic information about meerkats and addresses various aspects of their social behaviour, with an emphasis on the sentinels. The article is interesting, sometimes even humorous, just like the animals it talks about. It makes good material for discussions/debates on issues such as the evolution of co-operation in animals and in humans, and how animal and human altruism compare and contrast. The issue of social behaviour also creates the opportunity for interdisciplinary studies.

The article could give rise to many comprehension questions, including:

1. Why do researchers consider meerkats to be excellent model species for studying behavioural biology and ecology?


2. What are the benefits and the costs of group living for meerkats?


3. Why does Professor Tim Clutton-Brock say that meerkats are not altruistic?


4. Which main co-operative behaviours do adult meerkats contribute to?


5. How does the height of the sentinel’s post vary according to the environmental conditions present at the time?


6. Why are meerkats considered an excellent study system to test hypotheses arising from the theory of evolution?

Michalis Hadjimarcou, Cyprus