For cheetahs, walking around in a hot landscape costs more energy than chasing down prey.


Michael G. L. Mills

Wild cats need to count calories, too


Scientists have long wanted to know how large carnivores spend their days and how many calories they need to survive. Until now, researchers have had only rough estimates of the animals’ total daily energy expenditure. Yet this information is key to managing wildlife, says Terrie Williams, a wildlife physiologist at the University of California (UC), Santa Cruz. "For these animals, the bottom line is do you have enough calories to live and to reproduce? That’s been a missing piece of information."

Her group and another independent research team have taken some innovative steps to quantify energy use in wild cats. Williams and her colleagues developed a collar that monitors the movement and activity of pumas living in California's Santa Cruz Mountains, and they calibrated the collar by testing captive pumas on a treadmill. A different team spent weeks tracking cheetahs from dawn to dusk, analyzing the animals' feces to determine energy use. As a result, "they were able to more finely divide up the day in terms of the different types of activity the animals were engaged in," says John Laundré, a large carnivore ecologist at UC Riverside, who was not involved in either study.

Cheetah populations have plummeted in the last century, from about 100,000 in 1900 to about 10,000 today. Some researchers think lions and hyena are in part to blame for the decline. They are able to steal dead prey from the cheetahs, forcing them to spend what seems like an inordinate amount of energy in high-speed chases after more food.

To figure out if food theft was really a big problem, Michael Scantlebury, a conservation physiologist at Queen's University Belfast in the United Kingdom, and colleagues studied 19 cheetahs in two South African reserves. His team put radio collars on the animals, injected them with water with heavy hydrogen and oxygen atoms so these elements could be traced, recorded the animals' behaviors, and collected their feces to check for how fast those atoms were used, an indicator of metabolic rate. "We knew exactly where they were, what they were doing, and what they were eating," he says.

The cheetahs spent about 3 hours a day walking around—which uses up about 42% of their energy budget. They chase prey less than twice a day, about 38 seconds per sprint, Scantlebury and colleagues report online today in Science. "That [time for] energy expenditure is really short," Laundré says. "Either they catch them or they give up." And the cheetahs are successful catching prey about half the time.

Only four out of 43 times did the cheetahs lose their catch to hyenas or lions—not enough to put a strain on the cheetahs, Scantlebury says. He calculates that even if 25% of the prey were stolen, the cheetahs could compensate by just adding about an hour to the time they spent wandering around.

He worries, however, that in an effort to please tourists, game managers will increase the numbers of large predators in reserves, putting the cheetahs at greater risk of having their meals stolen out from under them. He found that cheetahs don't hunt when lions are nearby, or they move away—which could be energetically costly. Also, the data indicate that life would be tough on these animals if prey were scarce or inaccessible because of boundary fences that break up the landscape, forcing the cheetahs to spend a lot more time searching.

Williams and UC Santa Cruz ecologist and co-author Christopher Wilmers had long wanted to study the energetics of the local pumas. Unlike cheetahs, which hunt by day in very open landscapes, pumas are active at night in rugged territory and so are hard to watch. To monitor the movements of the cats, Williams and their colleagues developed collars equipped with GPS and devices that measure changes in acceleration and magnetic fields. By analyzing collar data for captive pumas walking or running on a treadmill, pouncing on dead prey, and going through their daily routines in a fenced yard, the researchers learned how to use the collar to figure out an animal's activity as well as its location. "It gives you information about a very secretive animal," Scantlebury says.


Video credit: T. M. Williams and L. Wolfe

The pumas spend about 2 hours a day looking for food. Some wander around quite a bit—and it takes a fair amount of energy for them to traverse the rugged terrain, Williams and her colleagues report online today in Science. Others just sit and wait. Of that time, the actual kill—a powerful pounce that can take down animals larger than the puma itself—takes just seconds in a high energy burst. And the pumas moderate the power of the bounce depending on the size of the prey, the researchers discovered.

"Ultimately the animals are using strategy to keep the [energy] cost as low as possible," Williams says. However, their results indicate that she and others have underestimated by 2.5 times what it costs these animals to make a kill. And wildlife managers should take heed. "If we’re going to have carnivores in a system we’ve got to provide what they need to live," she adds.

Those provisions should include not just enough prey, but the right landscape for capturing that prey, Laundré says. In that terrain, predators will expend less energy. “The better they are able to balance their energy needs, the better they will do."

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