Female Lions Are Democratic in Breeding, Study Finds
for National Geographic News
|July 26, 2001|
Motherhood is an equal-opportunity employer for female lions.
long-term study of lions in Africa shows that the females living among a
group of lions consistently produce similar numbers of surviving
offspring and raise them collectively.
Such egalitarianism is rare in nature. Most cooperative animal societies, such as mongooses and wolf packs, are despotic, leaving reproduction to a single, domineering female.
The researchers discovered that female lions form remarkably egalitarian societies that are characterized by two key features: symmetrical relationships and a voluntary system of communal cub-rearing in which all the qualified females engage in reproduction.
Because this reproductive pattern is so different from that of other cooperative animal groups, close study of the lions' behavior may improve scientists' understanding of the factors that lead to egalitarianism, said Craig Packer, a professor of ecology, evolution, and behavior at the University of MinnesotaSt. Paul.
Packer is co-author of a July 27 report in Science that describes the findings of the research, which lasted three decades and involved observations of lions at Serengeti National Park and Ngorongoro Crater, both in Tanzania.
Lions live in groups of three to thirty individuals, called prides. Within each pride is a group of closely related femalesmothers, daughters, sisters, and cousins. The number of individual females typically ranges from two to eighteen, depending mainly on how much prey lives in the surrounding area or migrates through a pride's territory.
Females do most of the hunting for the members of a pride and remain with the group for their entire lifetime, which can extend to 18 years. They mate and give birth to offspringusually one to three cubsevery two or three years, unless the cycle is disrupted by the invasion of males from outside the group.
Males, on the other hand, aren't so home-bound. They leave their native prides once they reach the age of two to four and band together with several other males, often from the same pride, to form a coalition.
Once the males in a group have reached full maturity and are ready to reproduce, they set off together to seek out an existing pride they can overtake. But first, they have to evict the males already living in the targeted group.
This confrontation is often violent and the weaker male lions are killed. The ousted lions that survive the rivalry go off in search of another pride to claim as their own. Male lions that manage to avoid early death can live to about the age of twelve.
Once the victorious males have taken over a pride, they kill all the existing cubsan act of infanticide that expedites a female lion's readiness to mate with one of the newcomers.
The new males stay around for several yearsusually up to four yearsto protect the group and its territory against other potential intruders. Eventually, however, a nomadic gang of males succeeds in overtaking the pride, and the cycle starts all over again.
"Life as a lion is pretty fast and furious," Packer noted.
In this tumultuous lifestyle, female lions equally share the burdens of childbearing and motherhood. This behavior, Packer and his colleagues say, is consistent with models of egalitarian theory.
Research into animal behavior has shown that egalitarianism is usually limited to species in which a single female is unable to control the reproductive habits of other females in the group.
That kind of control would be particularly difficult for lions to achieve, Packer explained, because the violent nature of their rivalry probably serves as a deterrent to despotic behavior. Potentially lethal claws and teeth pose a significant risk of what Packer calls mutually assured destructiona risk that's greater than in any other social species.
As a result, female colleagues in a pride don't harass one another or assert their dominance in social interactions, according to the researchers.
"On the one hand, they can be very aggressive to each other. They can be very dangerous companions to havethey are armed to the teeth, so to speak," said Packer. "On the other hand," he added, "there is some positive motivation to work together."
Female lions, like all feline species, slink off to give birth in secrecy. This keeps the young, vulnerable cubs away from potential female despots within the pride, and also hides them from nomadic males and predators such as hyenas.
Once a female lion has returned to the pride with her cubs, she raises them alongside other new mothers in a nursery group, or crèche. Only mothers with cubs of roughly the same age form a crèche. The advantage of this close association is that multiple mothers are available to defend the cubs against potentially infanticidal malesessentially, an instance of greater safety in numbers.
The researchers' data show that cubs are more likely to survive when they are raised in a nursery rather than by a solitary mother. This advantage of reproductive success gives female lions an incentive to synchronize their breeding, which they do.
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