Sexy Cats Can Take The Heat: Why Lions Have Manes and Other Tales from Tanzania
by Jennifer Amie
On the the plains of the Serengeti, a female lion awakened from a nap near a rock outcropping known as a kopje. Her sleep had been disturbed by the sound of a hyena feeding at a kill. Thinking she might amble over and steal some food, the lioness followed the sound, only to encounter a strange presence: two large but curiously immobile male lions with thick, dark manes. It was a sight she found even more arousing than the prospect of an easy lunch. Unfortunately, the attractive bachelors made no response to her advances. That's because the male lions were, in fact, life-size stuffed toys placed there by University of Minnesota researcher Peyton West.
West had deployed the dummies as part of a five-year research project in collaboration with University of Minnesota Distinguished McKnight Professor Craig Packer. Their goal was to answer a fundamental question about these large and social cats. Everyone knows that the lion is king of the jungle, and his mane is his crowning glory. But what purpose, exactly, does this shaggy headdress serve?
A mane is not only spectacular, but also unusual. "If you think about elaborate decoration on males, you think of birds, where males are flamboyant and females are drab," says Packer. "Among carnivores, male lions are the only ones that carry an extravagant ornament."
To find out why, Packer and West first examined the theory that the mane might serve to protect a lion's neck during an attack. Yet careful observation showed that the neck was neither a particular target during attacks nor an especially vulnerable spot if wounded.
"Once that theory was disproven," says Packer, "we turned back to Darwin." Charles Darwin first proposed the theory of sexual selection, which states that elaborate ornamentation comes at a price—by making a colorful bird more visible to predators, for example. By successfully bearing this "penalty," a decorated male signals to potential mates that he is a survivor, and a good candidate for fatherhood.
To test whether manes functioned to attract females, West devised an experiment involving life-size lion dummies. A Dutch toy company created the models based on hair samples and measurements provided by Packer and West.
Using a recorded hyena call to catch the females' attention, West strategically positioned dummies with light and dark manes and long and short manes to see which characteristics the females preferred.
Length, as it turned out, was not a deciding factor. Lions may have short manes due to age, illness, or a recent injury, but this doesn't matter to females, the researchers found. Color, on the other hand, really catches a female's eye. Manes range in color from blonde to black, with black being the most attractive of all. In her experiment, West observed that females were more likely to approach a dark-maned dummy, indicating his attractiveness. Males, in contrast, were more likely to approach light-maned males, presumably because they are less threatening.
West then set out to discover whether what she'd observed with the lion dummies would hold true for actual males.
In the natural course of things, a female lion's opportunity to choose a mate may, in fact, be limited. Males who find a female in estrus will guard her, keeping other suitors away. A male will guard only one female, however, leaving any additional, unguarded females free to choose a mate.
West observed lions in the field to determine whether dark-maned males attracted multiple mates. "When we saw a male mating with more than one female, we knew the extra female was there by her own choice, since a male only guards one female at a time," says West. "In 12 of 13 observations of males with multiple partners, the darkest-maned male was the favored choice."
Demographic records subsequently confirmed that by selecting dark-maned males, females were not choosing style over substance. Offspring of dark-maned males were more likely to survive.
"It turns out that darker-maned males really are studs," says Packer.
With higher testosterone levels and a better chance of surviving when wounded, dark-maned males excel at protecting their vulnerable cubs. "Sixty percent of cubs die before their first birthday," says West, "and most of that is due to attacks by males other than their fathers."
But if dark manes are so advantageous, why don't all males have them? The answer lies in Darwin's theory: having a dark mane must be costly in order to indicate strength. "Not everyone can afford that cost," says West. "That's what keeps the signal honest."
West and Packer theorized that darker-maned males suffered greater heat stress. "Imagine wearing a heavy muffler around your neck on a hot summer day," says Packer. "We thought the mane was a signal that these sexy cats can take the heat."
To prove it, West photographed lions using an infrared camera, which detects and measures heat. "We found a significant difference among manes," says West. "A dark mane makes you a lot hotter."
By solving the mystery of male machismo, West and Packer answered a fundamental question about an animal that plays a prominent role not only in its ecosystem but also in human mythology. Their findings were published in Science magazine and helped earn West her Ph.D. Today, West works as a curatorial intern at New York's Bronx Zoo, where she is researching Siberian tigers.
Packer remains director of the University of Minnesota's Lion Research Center and returned this summer to the Serengeti, where he has conducted research since 1978.
Over the years, Packer's research has spanned a number of topics, including genetics, physiology, behavior, and community ecology of lions. In recognition of his work, Packer was elected this year to the American Academy of Arts and Sciences.
He now is studying the ecology of infectious disease as part of a project funded by the National Science Foundation. The project was spurred by an alarming development: In 1994 a viral outbreak killed more than one third of the lions in the Serengeti.
To identify the cause of the epidemic, Packer combined his data with that of another Serengeti researcher, Sarah Cleaveland of Edinburgh University. Cleaveland was studying rabies in dogs, and her test subjects had begun to die of distemper. The scientists suspected that the canine virus might also be killing lions. DNA analysis confirmed their hunch.
Now, Packer is examining how such diseases spread among animal populations. At the same time, he's trying to do something to stop the spread. "My work is divided between applied and basic science," he says. "In infectious diseases, the basic research is fascinating but you've also got a direct and immediate application."
Packer and his colleagues are conducting a large-scale vaccination of domestic dogs living within a 10-kilometer wide belt around Serengeti National Park. The dogs are inoculated against rabies and distemper, protecting not only the canines but also the lions and preventing many human deaths from rabies.
"It's a good conservation program," says Packer. "It makes people safe as well as wildlife." He and his colleagues aim to vaccinate 75 percent of the area's domestic dogs—that's 30,000 dogs per year for five years.
Simultaneously, Packer is working on a second major project, also funded by the National Science Foundation, to study the "biocomplexity" of the Serengeti ecosystem. Packer heads a team of scientists from several American universities who are looking at how soils, plants, animals, and humans interact to produce the unique complexity of the Serengeti. They hope their data will inform local and national policy in Tanzania, as well as influence decision-making in individual households.
Among Packer's other lion projects is to understand how poaching and trophy hunting, along with harassment from Masai and farmers, affect the abundance of lions in Tanzania's national parks. By tracking lions with radio collars as they pass through Tarangire National Park and into human-occupied territories, Packer and his team hope to better understand the effects of conflict between humans and lions.
Studying lions, says Packer, yields much more than fascinating insights into the lives of these majestic cats. As the Serengeti's dominant predator, lions are an indicator of the overall health of their ecosystem. And Packer and West's mane study may even shed light on the effects of global warming. "We've found that how big a mane can grow depends on the weather," he says. In the Serengeti, the size of lions' manes has been shrinking over the past 30 years as global temperatures rise. Says Packer, "If climate change is affecting the ecosystem, one of the first places you'll see it is in lions' manes."