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ROARING, SOCIAL COMMUNICATION AND GROUP TERRITORIALITY IN AFRICAN LIONS.
A Review by
WHY LIVE IN GROUPS?
Lions are unique among the Felidae, as they are the only social wild cats. They live in prides of 2-18 adult females, with their dependent offspring and 1-9 adult males (Schaller, 1972). The adult males are not related to the females but may be related to each other and enter the pride from elsewhere. While juvenile males are forced to leave the pride form male coalitions and wander widely in search of another pride when they reach adulthood, females remain in their pride of birth or set up prides in nearby territories. Banishment of young males from the pride prevents inbreeding. African lions are cooperative animals. They hunt in groups, the females share food and raise and nurse each otherís young in a communal crèche (Pusey and Packer, 1994). Both sexes defend the prideís joint territory against other females and infanticide males. But why do they do this when most cats prefer a solitary existence?
It seems that lions achieve greater reproductive success by living in groups, nevertheless successful reproduction of this species also requires possession of a high quality territory (Packer et al., 1988). It is also interesting to note that males in larger coalition groups gain higher reproductive success than those in smaller coalitions, and females in medium sized prides have better reproductive fitness than those in very small prides. Therefore it is sensible to conclude that females in larger prides generally produce more surviving offspring. Living in groups also:
1. increases hunting success,
2. ensures defence of the young cubs,
3. helps to maintain territories in the long term,
4. ensures against individual injuries and
5. minimalises the chances of getting no food at all (tit-for-tat).
One female cannot defend a territory successfully alone and protect her young, so the smallest viable pride has at least 2 adult females, and so it seems that there is indeed safety in numbers. However, fighting to defend a territory, pride, food or young carries with it considerable risk of injury or even death (Schaller, 1972).
AVOIDANCE OF CONFLICT.
Lions have developed a type of social communication, which involves vocalisation which for the most part avoids confrontation and conflict, a far less costly approach. Males and females broadcast their territories by roaring. By listening to the number of roars, lions can gauge the strength of the opposition and react appropriately to the situation at hand.† At any one time, a high proportion of males do not possess a pride, and so they wander widely over pride ranges on their own or in groups until they succeed in taking over a pride of their own. Nomadic lions may incur considerable costs if they engage the attention of resident males, in fact coalition encounters may prove to be fatal for either side (Schaller,1972).On one hand, individual males may gain reproductive advantages by signalling to attract females or new coalition members, or simply to keep in contact with coalition partners, however, in doing this, depending on who is listening, they risk giving up their position to rivals and conflict may ensue (Grinnell and McComb, 1996). So one could reasonably conclude that under certain circumstances, it may be beneficial for non-territory holders to remain silent and avoid the costs of encountering hostile listening competitors, despite the obvious benefits vocalisation has for social cohesion and mating success.
DEFENCE OF THE TERRITORY.
In the early 1990s, Grinnell et al. (1995) observed that resident male lions consistently make aggressive approaches to playbacks of unknown males roaring broadcast in their territories. Playback experiments have also revealed that female lions are most likely to respond strangersí roaring if the number of females in the resident pride outnumber the outsiders. Interestingly enough, in responding to foreign roars, they also monitor each otherís behaviour while approaching the speaker (McComb et al.,1994, Grinnell et al., 1995). However males always advance towards the speaker regardless of the odds. Territorial defence may indeed involve a short term prisonerís dilemma, with joint defence being more effective than no defence (the reward is greater than the punishment for responding). During an inter-group encounter, a defector suffers fewer risks of injury however, than a co-operator (the temptation is greater than the ďsuckerísĒ payoff). A single defender can also repel a lone intruder when the temptation is greater than the reward (see student essay by Sophie Lowe, Krebs and Davies 1984).
Lionesses have been shown to adopt a variety of strategies when presented with unfamiliar roaring. These strategies range from cooperative territorial defence to lagging behind and letting other lions risk fighting (Heinsohn and Packer, 1995). Several studies suggest that lions cooperate unconditionally, rather than basing their responses on their companionsí behaviour. Grinnell et al (1995) found that males approached the playback speaker even when their companions were absent, thus cooperating even when their companionsí response could not be seen. However, on the other hand, Heinsohn and Packer(1995) found that certain females habitually lagged behind their companions when approaching the speaker. ĎLeadersí could distinguish between companions who were also leaders and companions who always lagged behind. Nevertheless when paired with a lioness who always lagged behind, a leader would still continue towards the speaker, arriving much earlier than the lagging lioness. Therefore leaders cooperated rather than defected in response to their partnerís defection and for some bewildering reason, did not physically punish a lagging lioness for failing to cooperate.
WHY DO MALE LIONS COOPERATE?
Male lions tend to only be in a pride for a very short period of time and so they need the support of their companions for future interactions e.g. Challenge by another male lion or a coalition (Grinnell et al., 1995). Therefore it is thought that this is why male lions cooperate at every opportunity in order to secure long term mutuality advantages. However, for the females, the territory is a long term resource that must be defended all the time, so any failure to defend the territory results in fewer resources for the future (Heinsohn ad Packer, 1995).
ASSESSING THE ODDS OF WINNING.
Robert Heinsohn (1995) made a comparative study of
lionesses in two contrasting African habitats in the early 1990s. He compared
lionesses in the Serengeti ecosystem with those of the adjacent Ngorongoro
TO ROAR OR NOT TO ROAR.
In another study (Grinnell and McComb, 2000), it was observed that nomadic male lions donít roar despite its importance in social ties with other males in their coalition and in reproductive success. They noticed that roaring is confined to males that are resident in prides and in particular to those that are prepared for conflict situations. They also noted that roaring is a flexible behaviour that is dependent on changes in status, for example resident males will remain silent outside their own territories and nomadic lions only roar when about to attempt taking over a pride, otherwise they remain silent to conceal their presence from eavesdroppers, even when separated from their coalition. Nomadic lions also failed to respond to playbacks of unfamiliar roaring. While non-resident males would benefit from roaring, by enhancing their ability to recruit and maintain contact with coalition partners, they refrain from doing so as the costs outweigh the benefits. Therefore nomadic lions will only roar when the probability of incurring costs, specifically the risk of attracting the attention of resident males in the area is low.
Lionsí short term decisions definitely do have long term consequences, however it is remarkable that one of the most cooperative of all the mammalian species on the planet, doesnít abide by the laws of reciprocity. Of course pride structure, home range and population density all correlate with food availability, foraging success and territorial defence in the lionís complex social system and influence the prideís cooperative behaviour.
Schaller, G.B.,1972. The
Serengeti Lion: A Study of Predator-prey relations.
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McComb, K, Packer, C, Pusey, A. 1994. Roaring and numerical assessment in contests between groups of female lions, Panthera leo. Animal Behaviour, 47, 379-387.
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Grinnell, J., McComb, K. 2001. Roaring and Social Communication in African lions: the limitations imposed by listeners. Animal Behaviour. 62, 93-98.
Heinsohn, R. Group territoriality in two populations of African lions. 1997. Animal Behaviour. 53, 1143-1147.
|Notes (if any) by Peter Kabai:|