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LUNCHTIME is supposed to be a slack period for wildlife-watching in
Africa. All animal activity seems to be inversely related to the arc of
the sun. As feeding, socialising and movement stop, animal watchers also
slow down – sometimes to write up notes and analyse data from busier times,
sometimes to fix vehicles and equipment, sometimes to catch up on rest.
As high noon approaches, the need for rest often wins out over the need
for vigilance.

After days of trying to record the activities of members of the Topika
hyena clan, we were too numb with fatigue to retreat to the coolness of
our camp. At 1215 hours the sun was burning with excruciating intensity
as we dozed in the inadequate shade of a lone tree. Observations over, we
were awake, but barely so. At the edge of our vision Lord Greystoke shifted
his position once again and lay down in a nest of longer grass, where he
had more shade but where we could no longer see him.

Lord Greystoke was an old, very bleached male hyena. His intact ears
and somewhat anorexic appearance suggested that he had never been a Tarzan.
We had him pegged as a peripheral member of the Topika clan. We had almost
forgotten him, when he got up and started to walk towards a group of resting
topi antelopes. Greystoke was probably too hungry to rest. Apart from us
nothing seemed to notice him, particularly not the inhabitants of Topika.

Topika is an ellipse of overgrazed turf that would not fill two football
fields. It would be difficult to find if it were not for three distinctive
trees on a nearby ridge. As suggested by its name, Topika is a good spot
for topi, large brown antelopes with distinctive sloping shoulders. The
four dozen topi bulls who frequented Topika had been joined that day by
a small group of cows, two with their 3-month-old calves.

Greystoke seemed so indifferent to the topi that we would not have been
surprised to learn that he was a vegetarian. We concluded that he was returning
to the muddy puddles from which he had been ousted by Topika’s resident
warthog family earlier that morning.

We turned away, then suddenly heard a topi calf cry. Greystoke had grabbed
it by the ear. He shifted his grip to the calf’s flank and two more hyenas
appeared as though from nowhere. Within seconds the three hyenas were eviscerating
the calf. By the time we had a camera in hand, they had ripped the calf
apart. Within five minutes more hyenas had arrived. A dominant pot-bellied
female ran off with the hindquarters; an unidentified male got most of the
rest. Greystoke was left with the head and neck and loped away, vanishing
into long grass a couple of kilometres away. All that remained of the calf
was a patch of grass stained with blood and undigested grass from its rumen.
After 9 minutes it was all over.

We were shocked. This sort of thing was not supposed to happen at midday.
The calf had been snatched from its mother’s side without so much as an
alarm snort. Was the calf already weak, sick, wounded, or simply unlucky?
Was the attack solitary and opportunistic or was it coordinated? The unscheduled
activity of our hyena brought up a whole host of questions.

Our educational touring company, Explore Mara, has been operating from
a base on the Olare Orok River in the north central region of Kenya’s Maasai
Mara since 1983. We run field courses in ecology for a number of North American
universities, and also offer other visitors the opportunity to observe animal
behaviour and gain a deeper understanding of the region’s ecology than is
possible on the average wildlife safari. Students and visitors alike participate
in our long-term study of the social and ecological effects of predator-prey
interactions in the Mara.

During the early stages of the study we did little sustained research
on the dominant predators – lion and hyena. The published work told us what
to expect. In the case of hyenas, this meant nothing at all during daylight.
Hans Kruuk’s pioneering study of hyena behaviour in the Ngorongoro and Serengeti
region (adjacent to the Maasai Mara) had shown that nocturnal hunting by
hyenas was as prevalent as, or even more common than, their scavenging.
Lawrence Frank, who studied the social behaviour of one clan of hyenas in
the Mara, confirmed Kruuk’s findings. Frank reported that hyenas were so
inactive during the day that he no longer did field work on them after 0900
hours and before 1700 hours.

So we concentrated on ecology. Instead of recording every detail of
predator behaviour, we simply kept notes on how to recognise individuals
and recorded their numbers in regular headcounts. These counts enabled us
to map out the structure and distribution of the potential prey populations
to anextent that had never been done before. Some significant characteristics
emerged: potential prey animals of several species often gathered in fairly
stable groups on areas of relatively short grass, even though they may have
been surrounded by a vast expanse of superior grazing. The most stable hyena
dens were those nearest the most stable clusters of prey species. We also
found that most of our sightings of lions and hyenas were within 1 or 2
kilometres of the most stable groups of prey.

These observations have led us to conclude that when predator pressure
is high, prey animals seek safety in numbers. In fact, we now believe that
gathering in mixed groups of different species is the prey’s main strategy
for avoiding KK being eaten in the Mara. We call such groupings Multiple
Species Associations, and recording their size and composition has become
a regular part of our study.

Most predators in the area are territorial residents, but among the
prey population the wildebeest and zebra are migrants and are absent for
six months of the year. This means that the resident herbivores are likely
to be picked off more frequently during this time. The counts showed that
three species, Thompson’s gazelle, impala, and topi, are the commonest resident
herbivores and so must bear the brunt of attacks by predators when the migrants
are absent.

For the next phase of our study we decided to examine how changes in
the degree of predation affected the behaviourand social organisation of
the resident herbivores. Weconcentrated on the largest and most numerous
residentantelope, the topi, Damaliscus korrigum.

Behaviour and risk

We started in the wet season of 1987 with an intensive investigation
of rutting behaviour. Most male antelope in the Mara defend large territories
with enough food to attract females. Topi are no exception, but we found
five places, one of which was Topika, where a large number of topi bulls
were defending very small territories with little or no food to attract
the females; these were communal mating grounds, sometimes called leks.
Lekking behaviour is rare among antelopes and might be an important clue
to the topi’s mating strategy.

The topi leks offered a rare opportunity to compare two mating strategies
in the same species. In 1987, two teams were in the field from dawn to dusk.
One team made detailed observations of topi activity throughout the day,
on and off leks; the other compared the ecological characteristics of lek
sites and sites where the topi had larger territories. These studies were
designed to define the factors that favoured a mating strategy based on
defending resources in one area,and on lekking in another. Greystoke’s attack
was the firstrecord of hyenas killing resting topi on the lek. We observedmany
more that season and they added a new dimensionto our study.

During May 1987 we recorded more than 30 attacks which proved fatal
for the victim. All took place between 1000 and 1500 hours, when the topi
were resting between the morning and evening grazing periods. A number of
these attacks happened on leks, so if lekking is an important breeding strategy
for topi, its rewards in terms of reproductive success would need to be
considerable to offset the cost of predation by hyenas.

But is midday predationby hyenas a direct cost of lekking? Some observers
have suggested that herding and rutting behaviour on the lek leaves the
topi exhausted and therefore vulnerable by midday. Our observations suggest
otherwise. We are convinced that it is disturbance and stress during the
night rather than lekking activity in the morning which puts the topi at
risk.

Hyenas attack most commonly at midday when the migratory wildebeest
and zebra are absent from the Mara, the time when predator pressure on the
resident herbivores is highest. Our night watches with image intensifiers
show that nocturnal attacks by lions and hyenas are so frequent during this
period that resident herbivores must remain vigilant throughout the night.
This in turn means that many predators are still hungry as dawn breaks.

The cool early daylight hours are a period of intense grazing for the
herbivores. The hyenas are resting, usually in long grass in very small
groups, or individually. After grazing, the herbivores begin to congregate
in multiple species associations on short grass. In the rutting season,these
resting places include leks. As the temperature rises, activity declines.
After an initial period of social interaction and rumination, most animals
shift to a resting position. Topi, in particular, lie down with the head
lowered and the chin resting on the ground.

As more and more animals take a nap, the hyenas move in and lie down
between 50 and 100 metres from the resting animals without attracting much
attention. By about 1100 hours individual hyenas begin searching for animals
so deeply asleep that they will not wake up as the predator approaches.
Typically, a solitary hyena makes a slow, seemingly directionless walk among
the resting animals, looking from side to side. The walk is as deliberate
as its intention is lethal.

That these walks are foraging attempts and not just changes of resting
place is supported by the fact that a hyena may walk for more than an hour
and then lie down just a few metres from where it started. Some teamwork
is also evident. As one hyena stops walking, another takes up the march.
Just a raised eyelid or a movement of the ear is enough for a hyena to monitor
the action. Resting hyenas can afford to relax fully, because, when the
time comes, the distress calls that follow a successful grab are a more
than adequate alarm.

Most potential targets simply get up and move out of range as the hyena
approaches, but not all and not every time. An antelope that remains in
the resting position will immediately become the focus of attention. The
hyena slows down to a more deliberate walk; as it draws close to the intended
victim it adopts a careful stalk, with head held low. At 10 metres or thereabouts
the hyena breaks into a run which rapidly becomes an open-mouthed charge.
It bites and hangs on to any point of contact.

The intended victim usually hears the charge, sees the attacker, and
leaps to its feet. Most escape, in which case the hyena pauses, changes
tack and then resumes its walk through the remainder of the resting assemblage.
But some targets do not wake in time. Their first and last alarm is the
pain of being eaten.

Within seconds of a successful grab, the frantic movement and bellows
of the victim usually attract other hyenas to the scene. Kills are most
certain when second and third hyenas arrive within a minute of the initial
attack. If other hyenas do not arrive promptly, the victim has a better
than 1 in 10 chance of survival. The hyena may be shaken off, or its teeth
may tear free, as the victim struggles and runs.

Survivors with amputated tails, or a variety of prominent scars on rump,
side and shoulder, were an early clue to how important predation by hyenas
is. (They were also a useful means of identifying individuals.) But such
escapees are rare. Typically, even topi bulls weighing 140 kilograms are
reduced to horns and hooves within minutes. Juvenile topi of both sexes
are the most frequent victims, followed by adult males on leks. Hyenas kill
relatively few adult females or adult bachelors.

The cost of sex

Adult males killed on leks by hyenas during the resting period are invariably
solitary and so pay a high price for their exclusive mating rights. Whenever
females are around, lekking males direct most of their attention to herding
and mating activities, even when the females are resting. Hyenas which approach
sleeping calves and females are chased away by the topi males. This defence
is an advantage to resting topi females, even though the cost is some initial
sexual harassment. But hyenas do take some females.

There is little evidence that topi act as sentinels for each other.
They rarely raise the alarm with a telltale snort. ‘Detection snorts’ seem
confined to instances in which topi bulls have females and calves within
their territories. Such snorts often precede head-down charges against the
attacking hyena. On the other hand, female topi remain silent even as they
watch a hyena taking their own calf. These attacks are usually so sudden
that they take the mother completely by surprise. By the time she sees the
danger and begins to defend her calf, it is too late.

The only effective alarm appears to be the sound of the hyena approaching
through the grass, and the sound and movement of nearby topi as they move
out of range. Joining a herd may be the only way to pick up such signals
and stillrest in relative safety. Animals resting within 5 metres of theirnearest
neighbour are at less risk from midday attack thananimals resting away from
their fellows.

We have observed the effect of midday attacks for each of the past three
wet seasons. Though most daytime attacks are against topi, we have also
seen hyenas take Thompson’s gazelles and impala at midday. We have seen
only one successful attack on a zebra foal. Daytime predation on sleeping
topi is not simply a cost of lekking, as we firstthought. We now know that
it happens more often awayfrom the leks than on them. Animals at the edge
of a mixedgroup of prey species are more likely to be eaten than thosenear
the centre (including the territorial topi on the edgeof a lek). Such assemblages
(including leks) may reduce therisk of attack on individuals and so have
important benefitsfor individuals.

Initially we felt that the hyenas were so successful because of a sudden
increase in their numbers in the area we were studying, and we expected
the success rate to drop as the prey animals learnt that a hyena at midday
is as dangerous as a hyena at midnight. But this has not happened. The only
measurable change is that the success rate declines as each wet season progresses.
Beyond that, attacks at midday appear to be an established feature of predator-prey
relationships in the Maasai Mara.

So why have the prey animals failed to develop a reliable defence against
midday predation? We believe that the hyenas’ annual switch between migrant
and resident prey is the principal reason. Resident topi are the main victims
of this hunting strategy, but they are at risk from it only during thesix
months of the year when migrants are absent. Thiscould be too short a time
for them to develop effectivestrategies for defence, and any that were developed
would beforgotten during the following six months, when thehyenas feast
on wildebeests and zebra. In short, it is notworth the effort of developing
a more effective daytimedefence against hyenas.

Michael Rainy and Judy Rainy operate an educational touring company,
Explore Mara Ltd, which runs field courses in ecology in Kenya. John Reader
is a writer and photographer. He and Michael Rainy are working on a book
on predation in the Maasai Mara.