Staying Close to Home - in Bequeathing Territory to Daughters, Solitary Leopards Provide a Glimpse into How Social Groups Evolved

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Londolozi Game Reserve, South Africa:

A 13-year-old leopard called The Mother gives birth to her ninth litter. At the same time, her adult daughter from an earlier litter delivers cubs in a den near her birthplace.

Masai Mara National Reserve, Kenya:

A 10-year-old female leopard named Half Tail roams a territory that overlaps with that of her adult daughter Beauty. Zawadi, another daughter from a more recent litter, lives just to the north.

Until recently, researchers delving into the lives of cats assumed that neighboring leopards were just that-neighbors. Now, they're discovering, there is more to these neighbors than meets the eye: In many cases, the females in an area turn out to be related, sometimes just as closely as lionesses in a pride.

Ordinarily, young mammals leave home when they become adults and move away to find a home range of their own. The process is called dispersal. But in leopards and many other mammals, the scientists are learning, newly in- dependent daughters often carve out a home range from a portion of their mother's range or squeeze in next to her. The name for this stay-at-home behavior is philopatry, a term derived from the Greek for "home-loving" and loosely defined as the tendency of an individual to remain in its birthplace as an adult.

The behavior is easy to see in lions, which travel together on open savannas where they can be observed by researchers. But as scientists complete long-term studies of other, more secretive mammals, they are finding some of the same dynamics. And so are wildlife photographers- including Lex Hes and Fritz Plking, whose pictures on these pages, from South Africa and Kenya respectively, help to record two leopard family trees not unlike those of lions.

Philopatry is actually not uncommon among mammals, says Peter Waser, a professor in the Department of Biological Sciences at Purdue University, but it is difficult to confirm. Scientists have now identified the behavior in tigers and other "solitary" cats, as well as in other mammals (see box, page 28). Their research problem is one of access over time. "People tend to accumulate one or two examples in a long-term study, but these observations are usually too few to publish in scientific journals," says Waser.

One exception is a long-term review of black bears by Lynn Rogers, a retired U.S. Forest Service biologist. Rogers' research in Minnesota involved following nearly 100 bears, all equipped with radio collars and ear tags, for more than 16 years. He discovered that as young female black bears become independent, their mothers essentially "give" the daughters a portion of their ranges.

By allowing her daughters to use her range, a mother black bear provides her offspring with an opportunity to forage in a good area and protects them from aggressive encounters with other bears. Knowledge of a feeding area, Rogers suggests, is very important for bears (starvation was the main cause of death for cubs and yearlings he studied). Young bears must be able to find widely scattered berry patches and other ephemeral food sources, and they may do so by remembering where they fed with their mothers when they were cubs.

The advantages of staying close to home vary for different species. Basically, however, the rationale boils down to familiarity: Remaining in a familiar area is safer than leaving. For young three-toed sloths, for instance, the motivation is familiar food. The sloths inherit the ability to detoxify and digest leaves of specific trees. They learn the location of those trees as they travel around with their mothers. When a young female becomes old enough to travel on her own, the mother bequeaths her a portion of her home range.

Familiarity can also increase a young female's chance of breeding successfully. …

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