Chapter 11
Making a living as a large carnivore poses quite a challenge. A sufficiently big herbivore must be found and killed every few days, year-round, despite the defences of these animals and competition from other carnivores for the most vulnerable prey. But carnivory need not be so demanding. All herbivores eventually die, and their carcasses become available to whichever meat-eater arrives first. Few carnivores pass by opportunities to scavenge on dead animals that they encounter. However, in order to secure sufficient food year-round, it may be necessary to kill animals a little sooner, before they die of advancing age or malnutrition. Hence mammalian carnivores regarded as scavengers also kill at times, generally selecting animals that are weakened and about to die soon anyway. The only obligate scavengers are birds like vultures able to scan vast areas on the wing to find the remains of animals wherever these might be located, including carcasses left by predators. Carnivores also take advantage of opportunities to steal carcass remains from those that did the killing, labelled ‘kleptoparasitism’.1 Thus, among large mammals, there is not such a clear division between predators that kill and scavengers that seek already dead animals.
Among primarily hunters, a distinction can be made between those that lie in ambush and those that chase down prey. The big cats like lions (Panthera leo) and leopards (P. pardus) typically hide in ambush, or stalk stealthily to within pouncing distance. Cheetahs rely on brief but fast chases to capture their prey. African wild dogs (Lycaon pictus) engage in long chases, as is typical of canids. Spotted hyenas (Crocuta crocuta) also undertake prolonged chases, but quite selectively, and shift flexibly between mainly hunting or largely scavenging in different regions. The next largest carnivore, the brown hyena (Hyaena brunnea), is primarily a scavenger, covering distances up to 40–50 km nightly to find carcasses.2
The prey species preferred by each of these predators is governed by relative size and whether the predator hunts in groups, or solitarily. Lions and wild dogs, and sometimes also spotted hyenas and cheetahs, hunt in groups, while leopards are strictly solitary hunters. Differences in hunting tactics affect how strongly kills are biased towards prey weakened by advancing age, illness or injury. Felids stalking stealthily kill a higher proportion of healthy animals than the cursorial chasers. In this chapter, I elaborate on the comparative hunting tactics and prey selection by these large predators, as well as their impacts on prey abundance.
Large Carnivore Profiles
The African lion (adult female weight 125 kg, males around 200 kg; Figure 11.1A,B) is the dominant predator over most of savanna Africa where large ungulates occur. Lions live socially in prides generally including 3–8 adult females and several cubs, with one or more adult males attached. Group coordination enables lions to hunt successfully in open savannas providing little concealment. Their tawny brown colour is clearly adapted to blend with dry grass, and even with green grass for colour-blind ungulates (Figure 11.2A). Lions preferentially kill prey in the size range 190–550 kg, particularly wildebeest, zebra, buffalo and, in more arid regions, gemsbok.3,4 However, smaller antelope like impala and springbok are under-recorded in kills because their carcasses get consumed completely. Male lions hunting separately from prides concentrate proportionately more on buffalo than pride females do.5 Adult buffalo were hunted only by prides containing five or more lionesses in Serengeti.6 Large prides can overcome even half-grown elephants weighing around 1500 kg,7 and in some places young hippos and adult giraffes are frequently killed. Lions focus their kills on adult ungulates, because calves provide too little food for more than the male lions in the pride. Young ungulates feature increasingly prominently among their kills of prey from zebra size upwards.8,9 In Ngorongoro Crater in Tanzania, lions depend to a greater extent on carcasses stolen from hyenas than is observed elsewhere.10 Baboons and monkeys rarely feature among lion kills.
Figure 11.1
The large carnivores. (A,B) African lion; (C) leopard; (D) cheetah; (E) African wild dog; (F) spotted hyena.
Figure 11.2
Carnivore hunting approaches. (A) Lion camouflaged in long grass, Maasai Mara NR; (B) lioness with giraffe brought down on a road, Kruger NP; (C) leopard melting into bush with impala it has ambushed, Kruger NP; (D) cheetah scanning open plains for prey to chase, Serengeti NP.
Lions hunt mainly at night, but may lurk in ambush near waterholes where ungulates congregate in the dry season during daylight.11,12 Their relative prey choice can shift in response to the changing vulnerability of particular ungulate species, dependent on rainfall conditions as well as habitat features.4 Buffalo are more prominent in kills made during the dry season and in dry years, when these formidable animals are weakened by food shortfalls. Wildebeest and zebra are less easily captured in dry years when the grass cover is reduced, because they can detect stalking lions at greater distances. Female ungulates feature more strongly in kills when handicapped by near-term foetuses or while giving birth, while male ungulates become more vulnerable to being killed while distracted by contests for mating opportunities.13 Shifting prey availability and vulnerability can generate oscillations in relative predator and prey abundance.14
The leopard (males 65 kg, females 40 kg; Figure 11.1C) is a typical ambush hunter relying on vegetation cover for concealment before pouncing on prey (Figure 11.2C). Their spotted pelage provides camouflage. They hunt mainly, but not exclusively, under cover of darkness. Leopards are distributed widely throughout Africa and beyond through tropical Asia, in both savannas and forests. Their preferred prey size range is 10–45 kg, i.e. medium–small or small antelope plus calves of medium–large ungulates.15 Primates feature prominently among their kills in rainforests, but baboons and monkeys contribute a much lesser portion than is commonly assumed in savanna habitats. Smaller carnivores, like jackals and domestic dogs, may also be killed. Leopards stash the carcasses of animals they have killed high up in trees to place them beyond the reach of lions and hyenas.
The cheetah (males 55 kg, females 45 kg; Figure 11.1D) is unusual among felids in being adapted for high-speed chases, including adept turns, to capture prey.16 They hunt typically, but not exclusively, in open grassland habitats (Figure 11.2D). Hunts take place mainly diurnally in the early morning or late afternoon, but occasionally also at night.17 Cheetahs frequently approach in full view, freezing when the prey look up, until they get within a range of 60–70 m before launching into a sprint. They typically reach speeds of 85 km/h, with a maximum of 105 km/h recorded. Cheetahs kill mostly prey in the size range 23–56 kg,18 thereby overlapping with leopards. Male cheetahs frequently hunt in coalitions of 2–3 individuals and can kill prey as large as adult oryx or kudu. Primates are absent from cheetah kills. Cheetahs typically feed only partially on carcasses before abandoning them. They seldom scavenge and are easily displaced from their kills by spotted hyenas or lions. Their ranges cover large areas in search of vulnerable prey.
The African wild dog (weight 25 kg; Figure 11.1E) fills the cursorial canid niche and hunts in both open and wooded savannas in large packs. Wild dog packs undertake hunts mostly diurnally in the early morning or late afternoon, thereby restricting losses of kills to hyenas and lions. Their prey size range extends from dikdik to female kudu (5–160 kg), influenced by pack size.19 Gazelles, impala and young kudu feature most prominently. Their chases after prey can be as short as 50 m, but may extend over 4 km. Animals in poor body condition feature more prominently in their kills than in the general populations of these species.20 Wild dogs rarely scavenge in the wild, but readily accept carcasses offered in captivity.
The spotted hyena (weight 70 kg; Figure 11.1F) operates either mainly as a hunter or more as a scavenger, depending on circumstances. Their dentition and cranial musculature are adapted for crushing bones left in carcasses abandoned by other carnivores. Spotted hyenas generally hunt nocturnally, probably due to thermal constraints, because they frequently dip in pools of water. They selectively probe for animals that are debilitated in some way – young, old or injured.10 Nevertheless, chases can extend over several kilometres, with a maximum of 24 km recorded. Hyena kills generally span the size range 50–180 kg, concentrated on the most abundant ungulate species available.21 In Ngorongoro Crater, packs of spotted hyenas actively hunt even adult wildebeest and zebra,10,22 perhaps enabled by the cool temperatures in this high-altitude caldera. In areas where lions are more effective hunters, hyenas obtain around half of their food by scavenging on lion kills.23,24 Spotted hyenas are less common in wooded savannas, perhaps because trees hamper their prolonged pursuits. In Serengeti, hyenas commute over distances of 30–80 km between their dens and the places where wildebeest congregate.
For all of these carnivores, food is most readily obtained during the dry season when herbivores lose body condition and take greater risks seeking whatever food and water remains. Carnivores experience lean times during the wet season when ungulates are in prime health and hence less easily captured, particularly by pursuit predators. Newly born calves can serve as a bridging resource, but only for a short period before these calves can also run speedily. All of the carnivores can obtain sufficient water from the carcasses of the animals they consume, and are thus not dependent on surface water, although they drink opportunistically.
In addition, there are the two small hyenas, functioning mostly as scavengers. The brown hyena (Hyaena brunnea) is restricted to southern Africa but has a wide range from the Highveld extending to the Kalahari and Namib coast. It covers distances averaging 30 km nightly in search of small carcasses, including remains of seals along coastlines, but only occasionally kills small animals.2 Brown hyenas supplement their largely meat diet with desert cucumbers, probably more for moisture than for food value. The striped hyena (H. hyaena) is more broadly omnivorous, scavenging for fruits and vegetable matter as well as various animal remains, plus hunting opportunistically.25 Its wide range extends from eastern Africa into parts of the Middle East. Its nightly forays covered mean distances of around 20 km in Serengeti. Both of these small hyenas have the ability to crush and digest smaller bones. Among the jackals, the black-backed jackal (Canis mesomelas) supplements hunting for mice, birds, baby gazelles and invertebrates with scavenging on remains of large carnivore kills, while the side-striped jackal (C. adjustus) is more omnivorous, consuming a mix of fruits, small vertebrates, invertebrates and carrion.
Killing Rates
Predator abundance along with rates of killing per predator determine the mortality rates imposed on prey populations. Allowance needs to be made for meat obtained from animals that had died of other causes. In Serengeti NP, half of the food eaten by lions was scavenged from carcasses of ungulates that had died or been killed by hyenas,26 but elsewhere lions generally kill the greater proportion. Moreover, not all hunting attempts are successful. The success rate of hunts by lions typically ranges between 15 and 30 percent.27 Prides typically numbering around eight individuals generally kill two or more wildebeest-sized ungulates per week, thus accounting for over 100 animals during the course of a year. This equates to 12 or more medium–large ungulates killed per lion (including cubs) per year. The ungulate population needed to sustain this offtake is 650 or more wildebeest-sized ungulates plus their offspring. If the exclusive core territory of the pride covers around 50 km2, this requires a year-round ungulate density of 15 animals per km2, across all prey species larger than impala. If the overall ungulate density is less than this, a larger core territory would be required, raising maintenance costs for patrolling. Hence lion prides establish territorial residence only in places where sufficient prey remain resident year-round. Lions may be encountered more widely, but these animals will be ‘nomads’, still seeking an opportunity to claim a territory.
Leopards attain a success rate per hunt ranging between 15 and 35 percent, almost identical to lions.28 Leopards need to kill an impala-sized animal almost weekly, and share kills only with offspring. Their projected kill rate is hence around 18 animals per leopard (including cubs) per year. The population of impala-sized prey needed to support each leopard is around 100 animals.
Cheetahs preferentially seek young ungulates less speedy than adults. In the Kalahari, fewer than half of the chases launched by cheetahs after adult steenbok or springbok were successful, but success rates approached 100 percent when juveniles of these small antelope were targeted.16 Because they do not consume carcasses completely, cheetahs need to kill every 2–3 days, projecting a kill rate per individual exceeding 50 animals per year. This requires a prey availability of around 300 ungulates per cheetah. Each cheetah thus needs to move over a much larger home range than each leopard. While the impact of cheetahs per capita on prey populations can be huge, it is alleviated by the low densities that cheetahs attain. Moreover, the flesh left on the carcasses they abandon helps feed other carnivores.
Wild dogs achieve a high prey capture success (around 45 percent on average)29 but remain surprisingly rare. They hunt almost daily. Allowing for pack size (typically about 10 adults plus pups), the annual kill rate per individual amounts to about 28 animals of impala size per year. However, their prey base is more narrowly restricted to the old and young segments of prey populations than is the case for the felids.30 Nevertheless, by hunting in a group, wild dogs can kill larger ungulates than female cheetahs or leopards do. Mortality inflicted by lions and leopards on ungulates of prime age reduces the proportion of herbivore populations surviving to old age, and hence the prey base for wild dogs. This explains why packs of wild dogs wander over home ranges encompassing 150–2000 km2 seeking vulnerable animals. However, wild dogs become restricted in the area they can cover while pups remain behind in dens.
The kill rate per spotted hyena, allowing for opportunistic switching between hunting and scavenging, may amount to around 9 medium-sized ungulates per year. Because of their highly selective hunting, testing for animals that are debilitated in some way, most of the mortality they inflict would be on old animals near the end of their lifespans. Consequently, the impact on prey populations would be lowered. However, newly born ungulates are especially vulnerable to predation by hyenas before they can run fast enough to escape, so in this aspect hyenas could have a much greater additive impact.
Overview
Only Africa still retains a full suite of stalking, coursing and scavenging carnivores. Lions are adapted through their social groups to hunt open savanna grazers and generally dominate the carnivore guild in prey biomass consumed (Figure 11.3). They are almost the sole predators on ungulates weighing over 150 kg in most places. Spotted hyenas shift flexibly between hunting and scavenging, using their bone-crunching jaws to subsist on carcass remains where lions dominate. Leopards, cheetahs and wild dogs hunt most effectively on ungulates smaller than those generally killed by lions, with their aggregate impact restricted by their low numbers. Kills by the cursorial hunters tend to be concentrated on the young and the old. Competition among these carnivores operates not simply through overlap in prey species killed; hunting by lions also restricts the proportion of prey populations surviving into the old age bracket when they become vulnerable to the cursorial hunters. Cheetahs and wild dogs range widely to locate the more vulnerable prey segments, constraining their abundance.
Figure 11.3
Size-structured predator–prey web in Kruger NP. Herbivore prey are grouped in body mass categories (shown in boxes) while the width of the arrows indicates how much prey biomass in these categories is consumed by each carnivore.
In South America, the carnivores hunting large mammals are restricted today to two solitarily hunting felids: jaguars (Panthera onca) in forests and wetlands, and pumas (Puma concolor) in woodlands and mountain slopes. Maned wolves (Chrysocyon brachyurus) obtain half of their diet from fruits and kill mainly rodents and rabbits. Spectacled bears (Tremarctos ornatus) found in forests are largely herbivorous, but supplement their vegetarian intake with some carrion. Australia once contained a carnivore called the thylacine, or Tasmanian wolf (Thylacinus cynocephalus), but it got exterminated following the arrival of the feral dogs known as dingos. During the Pleistocene, lions were present through most of Eurasia and even in the extreme north of North America, but today they persist beyond Africa only as a relict in dry bush in India. Cheetahs were formerly widespread beyond Africa through the Middle East, and cheetah-equivalents occurred in Europe and North America during the Pleistocene. North America retains cursorial canids in the form of the grey wolf (Canis lupus) and coyote (C. latrans) plus a single stalking felid in the form of the puma or mountain lion. Grizzly bears (Ursus arctos) do hunt baby ungulates before they can run fast, but otherwise operate as omnivores with opportunistic scavenging, like black bears (Ursus americanus). Tigers (Panthera tigris) and leopards are widely spread through Asia, while dholes (Cuon alpinus) remain locally in India as a wild dog equivalent. Largely scavenging carnivores, like hyenas, are missing from tropical Asia, perhaps because the wide travel necessary for this lifestyle is inhibited by the prevalent woodland. Wolverines (Gulo gulo) fill this role in the far north of Europe, as coyotes do to some extent in North America. Missing from Africa today is a tiger-equivalent, i.e. a solitary stalking felid matching the African lion in size.
SUGGESTED FURTHER READING
Mills, MGL; Biggs, H. (1993) Prey apportionment and related ecological relationships between large carnivores in the Kruger National Park. Symposium of the Zoological Society of London 65:253–268.
Radloff, FGT; du Toit, JT. (2004) Large predators and their prey in a southern African savanna: a predator’s size determines its prey size range. Journal of Animal Ecology 73:410–423.
Schaller, GB. (1972) The Serengeti Lion. A Study of Predator–Prey Relations. University of Chicago Press, Chicago.
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