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Sentinels: meerkat superheroes

Mico Tatalovic from the University of Cambridge, UK, investigates the private lives of meerkats. Why do these small carnivores live in groups? Why do they feed each other’s pups, dig together and guard each other? And what makes a really good sentinel?

lower is an internationally worry comes into her head: reproduc- Meerkats sunning themselves. Facclaimed television star. The Especially in winter months, meerkats ing. Such is the nature of natural Discovery Channel’s series Meerkat sun themselves to warm up in the selection: only those who survive Manor, the first ‘animal Big Brother’ morning before foraging, and in the long enough to reproduce will spread show, made her cute little face popu- evening before going to sleep their genes to the next generation. lar around the globe. Now a feature- Flower is a descendent of a long line length biography has also been Image courtesy of Mico Tatalovic of survivors. This means she has released with an accompanying book, adaptations that allow her to survive Meerkat Manor: The Story of Flower of despite the many predatory species the Kalahari. out to get her. Flower’s story only reached the Birds of prey, wild cats, jackals, world because of the research efforts snakes.... If it’s bigger than a meerkat of scientists based at the University of and it eats meat, it’s probably a threat. Cambridge, UK, who set up the Living in a group is an advantage; Kalahari Meerkat Projectw1 15 years many eyes see better. But meerkats ago and have studied the lives of sev- have evolved an even more sophisti- eral meerkat groups daily ever since. cated strategy to avoid predation: Such long-term field projects have posting sentinelsw2, usually one but become popular in the field of behav- sometimes several at the time. Like ioural biology because they permit soldiers on guard, meerkat sentinels the accumulation of an enormous scan the horizon from an elevated amount of data on every aspect of post and announce their duty with a animals’ lives, allowing scientists to special sentinel call, the ‘watchman’s ask and answer ever-more detailed song’. They have excellent depth per- questions about their evolution. ception that allows them to see preda- When not on camera, Flower, like tors at a great distance. Having a sen- other meerkats (Suricata suricatta), has tinel on guard reduces the possibility to worry about two main things in of surprise attacks and allows the rest life: finding food, and avoiding being of the group to be less vigilant. eaten herself. When the right time Sentinel behaviour may seem altru- (and the right male) comes, a third istic since the sentinels help others at

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Cutting-edge science

Meerkat research

The Kalahari Meerkat Project was set up some 15 years All pups are caught and an identity microchip is inserted ago by Professor Clutton-Brock from the University of under their skin in case the dye marks on their fur wear Cambridge, UK. Since then, the Cambridge scientists have out. Blood samples are also taken at regular intervals collaborated with colleagues in other countries, especial- throughout their lives, to obtain both their DNA and hor- ly at the University of Zurich in Switzerland and Pretoria monal profiles. This helps researchers to determine rela- University in South Africa. tionships within and between the groups and to correlate All meerkats involved in the project are wild but habituat- behaviours with hormone levels. The animals are captured ed to people and are easily identifiable by small dye marks for only a few minutes, to avoid stressing them too much. that the researchers and volunteers have painted on them. For the scientists, a typical day of meerkat research These dye marks make for easy identification, as ‘head and involves waking up before sunrise to arrive at the sleeping shoulders’ is different from ‘right rib, right thigh’. Familiar burrow before meerkats get up. Various records have to be with people since birth, the animals ignore us so we can kept, such as where the animals slept, when they got up, observe them from as little as 0.5 m away and walk among how heavy they are (we use small crumbs of hard-boiled the group without disturbing their normal behaviour. Since egg to lure them onto scales, saying “yum, yum, yum!”). most meerkats are studied from birth, each individual’s We also count and identify all the animals to check the parentage and life history is recorded. group’s composition and then follow them for three hours The project manager makes a weekly schedule of group while they forage for food and avoid predators. When fol- visits to allow researchers (master’s students, PhD students lowing them, we also take regular GPS readings to calcu- and postdoctoral researchers) to visit the meerkat groups late the routes that the meerkats take on their foraging

they need for their experiments and to make sure all trips. At midday, when the meerkats have a siesta to avoid Image courtesy of Mico Tatalovic groups are visited at least a couple of times a week by vol- the heat of the desert sun, we leave to have lunch and unteers to keep track of where the animals go and what return in the afternoon for more data collection. Afternoon they do. In every group, one animal has a radio collar that experiments might include playing the meerkats’ own allows it to be tracked; most of their sleeping burrows are vocalisations back to them or presenting them with pred-

BACKGROUND also labelled with GPS points so it is easy to locate them. ator cues or faeces to observe their responses.

Meerkats resting. In the summer months, meerkats rest at midday to avoid the heat

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Meerkat society

Meerkats (Suricata suricatta) are small, carnivorous Meerkats reach adulthood at around one year of age. At mammals weighing on average less than one kilogram. around 18-30 months of age, males voluntarily leave the They inhabit the arid areas of southern Africa and live in group, either to join an existing group or to form a new social groups of 2-50 individuals, consisting of one dom- group with unrelated females. Adult females, particular- inant pair and a variable number of subordinate helpers ly pregnant ones, may be evicted from their home group who may or may not be related to the dominant pair. by the pregnant dominant female; this is thought to These members of the mongoose family (Herpestidae) reduce the chance of the dominant female’s pups being eat mainly arthropods (insects, spiders and their rela- eaten by the other females. Most females return to the tives), as well as the occasional small mammal, reptile or group once the dominant female has given birth, but plant bulb. some may permanently disperse to form new groups They have territories with several sleeping burrows, from with unrelated males. which they make daily foraging trips of up to a few kilo- Dominant meerkats live for 6-10 years on average, with metres. Depending on food availability and predation the oldest individual in the Kalahari Meerkat Project pressure at specific spots, they will either return to the being almost 13 years. The age of subordinate meerkats same sleeping burrow for several nights, or change bur- is more difficult to record, as many disperse or are rows quite frequently. evicted by the age of around three years, and are subse- On average, litters consist of three to four pups that stay quently lost to the project records. The most important within the burrow until they are approximately three known causes of death are predation, fights with other weeks old. During that time, while the pups are being meerkats (including infanticide), diseases and human- fed on milk, the group returns to the same burrow. At caused factors such as car fatalities – but for two-thirds four weeks of age, the pups begin travelling with the of the Kalahari Meerkat Project meerkats, the cause of group and for their first three months of life, are fed on death is unknown, since the individuals just disap- invertebrates and small vertebrates by helpers. peared. BACKGROUND Image courtesy of Mico Tatalovic their own expense: when they are meerkats, to give us preliminary guarding, they not only expend energy answers and to help us formulate and and lose valuable foraging time, but test theories. also expose themselves to predators. Flower keeps guard from trees, But are they really being altruistic? logs, bushes, grass tufts or even My research group investigates con- human heads. The average height of flicts and co-operation in meerkat the posts from which meerkats keep societies, and as part of this work, I guard is around 60 cm although the focus on sentinels. One of the main bravest sentinels will climb trees up questions I am investigating is why to six metres high. The height of the some meerkats spend more time on sentinel’s post also varies with the guard than others. An answer to a vegetation cover; during the rainy simple question like this can give us season when grass is tall, sentinels valuable insights into the evolution of guard from higher posts so that they Meerkats at a sleeping burrow. Sleeping social behaviour. ‘Why are some can see above the grass. This reflects burrows may have several exits and humans more social than others?’ and the fact that the behaviour of wild rooms inside. Meerkats maintain them but don’t dig them; instead they use ‘How did our sense of community animals is affected by their environ- ground squirrels’ burrows and sometimes and helping others initially evolve?’ ment; when studying behaviour, it is also share them with yellow mongooses we may ask eventually. Until then, we often important to consider the envi- that live in small family groups study model animals, such as ronmental effects.

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Cutting-edge science

Meerkats are an excellent model species for studying behav- Costs of group living ioural biology and ecology because they can be habituated There is a trade-off for individuals between the benefits and to close observation by humans; they are also diurnal and costs of group living. One of the main costs of group living forage in a relatively open habitat and are hence easy to fol- is the prevention of reproduction: the dominant breeding low and observe on foot. The aspect of their lives that inter- pair accounts for around 80% of the offspring born to the ests evolutionary biologists the most is their sociality. Why group. Dominant females try to weight the reproduction in do they live in groups? Why do the young adults stay in the their own favour, so that they produce as many offspring as group and why do they help each other? What are the evo- possible; subordinate females are commonly expelled from lutionary conflicts among individuals living in groups and the group by the dominant female in the latter half of her how are these resolved? pregnancy to prevent infanticide by subordinates. Subordinate females are also evolutionarily driven to repro- Benefits of group living duce, in spite of attempts by the dominant female to prevent this from happening. Similarly, subordinate males try to find For meerkats, group living makes sense because there is receptive females from neighbouring groups and thus little available land for establishing their own territories, enhance their reproductive success. most of the appropriate habitat having already been taken by rival groups, and the harsh desert environment makes it The exact nature of these within- and between-group con- difficult to survive alone. All adult meerkats contribute to flicts and resolutions is a subject of continuing research. co-operative behaviours; the main ones are pup feeding, Currently, scientists are looking at the way in which differ- sentinel duty, burrow maintenance and, for females, allolac- ent hormones such as oxytocin (the ‘trust’ hormone) affect tation (lactating for another meerkat’s pups). Co-operation social behaviour and conflicts within the group. Others are increases the pups’ survival, development and subsequent examining the influence of an individual meerkat’s person- reproductive success, which benefits the group as a whole, ality on its behaviour and decisions. because larger groups are more likely to survive.

Sentinel behaviour also differs check the surroundings for anything increase or decrease in cortisol levels between individual meerkats. Some suspicious. It seems that these super- – by introducing the hormone into the sentinels will go on guard more often, sentinels also have higher levels of animal’s system or blocking it through and guard longer and from higher the stress hormone cortisol. This rais- the introduction of another molecule posts: this is why we consider them to es the question of whether this hor- – changes meerkats’ behaviour.

be ‘supersentinels’ – although we mone is the cause or the effect of their But why do we devote so much Image courtesy of Eleanor Harris don’t actually know if these individu- behaviour. Future research could time to elucidating meerkat behav- als are also the most efficient in address this by observing how an iour? Studying specific behaviours detecting predators. The longer they such as guarding is like fitting a sin- stay on guard, the more likely they gle piece of puzzle into the larger pic- Meerkat guarding are to announce their alertness when from the top of a ture of the evolution of social behav- protecting the group, so that the dry branch iour. Eventually we would like to group can relax. Supersentinels are understand how, why and when co- also likely to be animals that are usu- ally more vigilant; even when they are not on sentinel duty, they often stop while foraging for food to briefly

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lutionary biology is the existence of main causes of the evolution of this altruistic behaviours in humans and social, apparently altruistic behaviour. animals. Darwin’s theory of natural However, we still don’t know exactly selection argues for the survival of the why meerkats guard and why some fittest through competition for limited are just so super at it. The current resources (food, mates, space). Yet, we hypothesis is that good foragers – find animals such as meerkats co- meerkats that are the most efficient at operating happily; they baby-sit and capturing prey – are also the best sen- feed (even lactate for) other meerkat’s tinels, because they spend less time pups, dig burrows together and foraging and thus have more time guard the whole group from predator and energy to spend on other activi- attacks. How can Darwin’s theory ties. But the evidence is still too scarce explain the observed harmonious to support this. My research might Image courtesy of Mico Tatalovic Image courtesy of Mico lives of meerkats? help elucidate some of the answers to Meerkats emerging from a bolthole after After 15 years of detailed study of these questions. I just hope they’re a predator alarm meerkats, Professor Tim Clutton- not doing it only for the cameras! w3 Brock of Cambridge University and operation evolved in animals and in his colleagues say that meerkats are our own species. We would like to not that altruistic after all. There is a References know why we are so different from lot of selfish behaviour going on. A Clutton-Brock TH et al (1999) Selfish other animals. We would like to probe classic example, published in the jour- sentinels in cooperative mammals. deeper into the evolution of life on nal Science, is the finding that meerkat Science 284: 1640-1644. doi: our planet and to satisfy our thirsty sentinels guard from safe sites, and 10.1126/science.284.5420.1640 curiosity. “Why?” It’s the question only once their bellies are full that drives science. (Clutton-Brock et al, 1999). Moreover, Meerkats are an excellent model being the first to spot predators Web references system to test hypotheses arising means that in most cases they are the w1 – For more information about the from the theory of evolution. One of first to escape them too. This suggests Kalahari Meerkat Project see: the biggest unsolved problems in evo- that direct, selfish benefits are the www.kalahari-meerkats.com Image courtesy of Mico Tatalovic Image courtesy of Mico

Meerkats sunning themselves

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Cutting-edge science

Image courtesy of Eleanor Harris Mobbing a snake: Mobbing is used to gather information about a threat and to chase off potential predators

w2 – To watch a video clip of meerkat Resources sentinels on the Discovery Channel For more information about meerkats, Mico Tatalovic is studying for a website, see: see: master’s degree (MPhil) in the http://animal.discovery.com/ Department of Zoology at the The Fellow Earthlings’ Wildlife fansites/meerkat/video/video.html University of Cambridge, UK. Center, which specialises in caring (note that you may have to watch Originally from Croatia, he was for meerkats: an advertisement before the video awarded a scholarship, first to study www.fellowearthlings.org clip appears) at the University of Oxford, UK, and w3 – For more information about the The East Coast Meerkat Society: then at Cambridge. work of Tim Clutton-Brock’s www.meerkatsrule.org research group, see: www.zoo.cam.ac.uk/zoostaff/larg/ Pages/

This article provides some basic information about 2. What are the benefits and the costs of group living meerkats and addresses various aspects of their social for meerkats? behaviour, with an emphasis on the sentinels. The arti- 3. Why does Professor Tim Clutton-Brock say that cle is interesting, sometimes even humorous, just like meerkats are not altruistic? the animals it talks about. It makes good material for 4. Which main co-operative behaviours do adult discussions/debates on issues such as the evolution of co-operation in animals and in humans, and how ani- meerkats contribute to? mal and human altruism compare and contrast. The 5. How does the height of the sentinel’s post vary issue of social behaviour also creates the opportunity according to the environmental conditions present for interdisciplinary studies. at the time? The article could give rise to many comprehension 6. Why are meerkats considered an excellent study questions, including: system to test hypotheses arising from the theory 1. Why do researchers consider meerkats to be of evolution? excellent model species for studying behavioural Michalis Hadjimarcou, Cyprus biology and ecology? REVIEW

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