A cheetah walking in the Kgalagadi Transfrontier Park, South Africa/Botswana. The cat uses much of its daily energy budget searching for prey. | Michael G.L. Mills
Mid-sized carnivores like cheetahs and pumas spend more energy searching for prey than chasing it, according to two new studies of the animals in their natural habitats.
But, this energetic balance could be upset by human disruptions of the cats' hunting grounds, such as fencing, that threaten the cats' survival in the wild.
David Michael Scantlebury from Queen's University Belfast in Northern Ireland and colleagues from around the world studied cheetahs in Africa while Terrie Williams from the University of California, Santa Cruz, and her team focused their attention on pumas hunting in the mountains. Together, the researchers paint a vivid picture of these mid-sized predators' hardscrabble lives.
Their results, based on years of field work and detailed data from sensitive radio collars, appear in the 3 October issue of the journal Science and reveal how finely-tuned these hunters really are.
"Olympic sprinters expend a lot of energy to stay fit and maintain their bodies, and you'd imagine that cheetahs have to do the same," said Scantlebury. "But we looked at their energy expenditures, based on their behaviors, and the main correlation to energy was how far they walked to find prey."
A cheetah chases springbok in the Kgalagadi Transfrontier Park, South Africa/Botswana. | Michael G.L. Mills
"So if you disturb a cheetah on its hunt or if anthropogenic factors change its landscape to a field with fences or a farm with dogs and a shotgun-toting farmer, you figure a cheetah is going to have to walk around more to avoid these nuisances and, in doing so, expend a lot more energy," he said.
Scantlebury and his colleagues studied 19 cheetahs in Africa for weeks at a time, recording their behaviors such as lying, sitting, walking, and chasing prey throughout the day. Using ratios of hydrogen and oxygen isotopes in the cats' excrement, the researchers were able to estimate the cheetahs' daily energy expenditures.
"We have behavioral data because we followed these cheetahs every day for two weeks at a time and saw what they killed, what they ate, whether they fought over the meal or if a female was in heat," said Scantlebury. "We went out every day, hour after hour in the baking sun, and watched these animals, wondering, 'When are you going to poop?'"
Surprisingly, the researchers found that cheetahs don't spend much more energy than other similarly-sized mammals — and that their biggest energy drain doesn't come from their infrequent sprints, but simply from walking around in search of prey.
Scantlebury and his colleagues were also concerned about the effects of kleptoparasitism, or the theft of meals by larger carnivores, on cheetahs' energy budget. The researchers discovered that cheetahs were extremely well-adapted. Even when 25% of their meals were stolen, cheetahs only had to go back out and hunt for another 1.1 hours, upping their daily energy expenditure by just 12%.
Pumas, on the other hand, have adopted a more patient approach to hunting over the years, according to Williams and her team. The researchers developed a new SMART collar (which stands for species movement, acceleration and radio tracking) that follows the predators' movements while measuring oxygen consumption and monitoring GPS information.
Pumas trained on the treadmills in the Santa Cruz study eventually learned to run with ease at different speeds. | T.M. Williams and L. Wolfe
Williams and her colleagues calibrated the collars with three captive pumas that they trained to walk on treadmills — a tricky and time-consuming task — before they fixed SMART collars to four wild pumas in California's Santa Cruz Mountains to collect data on the cats' hunting behavior.
The researchers' findings show that pumas spend about 2.3 times more energy locating prey than researchers had predicted. The cats balance out this expenditure by lying in wait and then precisely matching the force of their attack, or pounce, to the size of their prey.
"The pounce provides a remarkable, powerful kill that enables these individual pumas to bring down prey that is two to three times their size," she said. "The more time that the animals could spend in low activity level behaviors, such as stalking, sitting and waiting, and slowly walking, the greater the relative benefit of the kill."
A test of the puma's pounce on an elk leg at normal speed and slow motion demonstrates the power of these cats. | T.M. Williams
But if the pumas' habitat is altered and it becomes more difficult for them to hide, the cats could have a much harder time hunting, according to the researchers. In that way, humans have the potential to offset the delicate balance that these wild cats have struck with nature over thousands of years of evolution, they say.
"We are hoping that these new SMART collars will give us greater insights into the biological needs of these unique cats, and that conservation measures and habitat plans will incorporate their species-specific biology into management schemes," said Williams.