With an earsplitting roar that rolls more than three miles across the Serengeti, the “king of the jungle” fluffs his mane, stretches his neck and asserts domination over his territory. If decades of children’s books and Hollywood movies haven’t ingrained this name and image, the 1994 Disney animated film hit “The Lion King” did. Never mind that lions don’t live in jungles, that a pride doesn’t have a king, or that the territory belongs to the females; the image persists.
Prides consist of long-lasting, complex social groups with up to 18 closely related adult females, and subadults and cubs of both sexes. They hunt cooperatively, eat cooperatively, and defend and care for cubs cooperativelyeven to the extent that any female will nurse any cub in the pride.
Male lions also form cooperative social groups, smaller ones called coalitions. A coalition joins a pride, fathering all the cubs during their tenure. For most males, this temporary residence in a pride represents the once-in-a-lifetime chance to father cubs and pass on their genes. Once a male leaves a pride, he has little chance of finding a place in another. These high stakes cause competition to take on life-and-death importance for male lions, and a coalition remains in a pride only about two to three years before being ousted by a new, more powerful coalition.
Photo © 2004 Karyl Whitman, University of Minnesota
One result of this intense competition is the willingness of male lions to attack, and sometimes kill, males intruding on their territory. A more grisly result is that a new regime systematically kills all young cubs and drives away all subadults in a pride. The loss of their young causes females to come into heat sooner, boosting the opportunities for new males to mate. Researchers estimate that attacks by adult male lions cause nearly a third of all cub deaths. (Females rarely attack cubs.) A third result is the formation of coalitions themselves. No one lion, no matter how powerful, can protect his interests alone. He needs partners. Two or three unrelated males may form a coalition, all sharing in the fathering of cubs. It’s a win-win situation wherein males do best by cooperating unconditionally. Larger coalitions form as well, but this decreases the chance for an individual male to father cubs, so larger groups always contain closely related males. That way if a male doesn’t father a cub, at least he’s protecting cubs that are genetically related to him.
Females compete as well, but for long-term ownership of a territory. Encounters with intruding females more typically include a chase, rather than an attack, and the intensity is much lower.
Both male and female lions would benefit by knowing exactly who any given lion is. For a male, attacking a member of his own coalition roaring at the boundaries of the territory would weaken his coalition and might end its reign. But attacking one or more intruders from another coalition can make the difference between passing genes to the next generation or not. To make this distinction, lions should be able to distinguish the roar of a friend from the roar of a foe.
Jon Grinnell, Craig Packer and Anne Pusey, all of the University of Minnesota, and Karen McComb of the University of Cambridge, decided to find out just how well lions hear and understand roars. Armed with tape recordings of roars of foreign lions, a high-quality playback system, and a stuffed lion, they set out for Serengeti National Park in Tanzania. They studied a population of about 200 lions in 20 prides that have been under observation for 20 years. Each lion bears individual natural marks, making identification possible.
The researchers asked two sets of questions:
Many studies of birds and some of fish and mammals have revealed that adults can identify other adults of their own species. But scientists have had a hard time explaining just what the immediate survival benefit of such recognition is. The lion studies provide a potential answer. By recognizing an intruding male lion by his roar, a female could save the lives of her cubs, an immediate genetic benefit. Although she will have new cubs with new males eventually, her best strategy is to ensure that the cubs survive long enough so that invading males will merely chase them away instead of killing them.
In the study of females, the team set up a loudspeaker in brush more than 200 yards from a pride. They played recorded roars of the fathers of the cubs, roars of male lions living about 20 miles away and unfamiliar to the pride, and roars of unfamiliar female lions. They found females remained calm when they heard the roars of their current mates. (This was the first research, to the team’s knowledge, to show that an animal can recognize its mate’s call.) But when they heard the roars of unfamiliar males, they would snarl and immediately move toward their cubs to begin a timely retreat. If their cubs were too small to retreat quickly, or were safe in a den, the females stood their ground near the cubs. Pusey and Packer have shown in previous research that the strategy works. Takeovers by new male coalitions rarely succeed unless most of the cubs are too young to travel quickly (under about six months).
Females reacted differently to the roars of unfamiliar female lions. They approached the speaker, sometimes even leaving their cubs behind to do so. But they didn’t approach willy nilly. The females apparently could assess the number of females on tapethe recordings included single roars and choruses of two or three animalsand figure the odds. They never approached unless the odds were about two to one in favor of the home pride. With lower odds, the females either did nothing or roared in an apparent attempt to recruit absent members of their pride. When they did approach, they did so faster and less hesitantly when the odds were more heavily in their favor. The females balanced the value of their territory against the risk of harm should they approach and attack the intruding females.
The researchers also played roars from a single male lion or from two or three males roaring together. They played roars either from a speaker concealed in brush or in a stuffed male lion. Male lions appear exquisitely aware of exactly who is roaring, clearly distinguishing coalition members from intruders. When faced with a foreigner, resident males adopted an entirely different strategy from that of females. No matter what the odds, male lions aggressively approached the roaring speaker, in three cases attacking the stuffed lion. If a new coalition were to succeed in taking over, not only might they lose the cubs they’d already fathered, but also lose any future chances at fatherhood. Males depend on their coalition for their one chance at reproductive success, so no matter what the risk, they cooperate to defend their joint fatherhood (a far cry from the image of a scheming subordinate male plotting to oust the monarch portrayed in “The Lion King”).