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發表於 2013-7-26 10:13 AM
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本帖最後由 colourbeast 於 2013-7-27 10:46 AM 編輯
Like a finely tuned sports car, cheetahs are precision machines born to run. But for over 30 years, researchers believed the animals' blazing speed came at a cost—the danger of overheating on a hunt.
A 1973 study looking at captive cheetahs running on a treadmill found evidence that these sprinters abandoned hunts because they got too hot. That gave birth to the idea that the animals' hunting success rate was due to the fact that their motors ran a little too hot. About 40 to 50 percent of cheetah hunts end in a kill, which is on the lower end of success rates among African big cats.
"It became a popular story that got applied to free-ranging cheetah," said Robyn Hetem, a biologist at the University of Witwatersrand in Parktown, South Africa. "Most of our guides will tell you this when you come to Africa and see cheetah."
Not so fast, says a new study published July 23 in the journal Biology Letters.
Study leader Hetem and colleagues found that the body temperatures of four free-ranging cheetahs stayed relatively stable during the chase portions of successful and unsuccessful hunts.
Body temperatures rose after the cheetahs stopped running—but they rose about twice as much in individuals that had brought down prey, compared with ones that had abandoned a hunt. (Watch National Geographic's slow-motion video of a cheetah running at top speed.)
Hetem and colleagues saw this rise after controlling for factors including the duration of a hunt, activity levels during a hunt, and air temperature.
"I've never been convinced by this idea that cheetahs overheat when they're chasing, so it's nice to see that confirmed," said Sarah Durant, an ecologist at the Zoological Society of London who also sits on the committee for National Geographic's Big Cats Initiative.
"What does surprise me is the temperature rise after they've killed," added Durant, who wasn't involved in the research.
Stressed Eaters
Hetem and colleagues were able to monitor body temperatures and activity patterns of these sleek carnivores by implanting sensors in six cheetahs living at the Tusk Trust Cheetah Rehabilitation Camp in Namibia. The scientists ended up using data from four because a leopard killed two of the six study animals.
The researchers hypothesized that the post-hunt temperature rise was due to a stress response in cheetahs on the lookout for other predators.
"In the Serengeti where I work, it's very common for hyenas to be attracted to the sound of a chase or the kill," explained Durant.
Cheetahs are very alert after a kill and when they're eating, she said. "They spend a lot of time sitting up, presumably looking for other predators."
Many times cheetahs rest or wait before tucking into a meal, and it was during these periods that Hetem and colleagues saw the body temperature increases. The rises would peak about 15 minutes after unsuccessful hunts and 40 minutes after successful ones.
Similar Siblings
Hetem discounts digestive processes as an explanation for the body temperature increases, since they occurred while the cats were eating as well as resting or waiting near their kill.
Previous studies have seen increases in the body temperatures of deer and impala when they are exhibiting fear. So a similar stress response in cheetahs could help explain why there's a greater increase in body temperature after successful hunts versus unsuccessful ones, Hetem said.
This is further supported by the fact that one of the study cheetahs got a thorn lodged in a paw one day and did not participate in a hunt at all—his sister made the kill. But the male did share in her spoils.
"He shows the same body temperature pattern that she does," said Hetem. "The rise in temperature happened when he got to the prey item."
Lunch Break
This stress-response explanation is an interesting hypothesis worth further investigation, Durant said.
She added that it's important to know how hunts affect cheetah body temperatures because of a curious effect of humans on cheetahs in the Masai Mara National Reserve in Kenya. (Related: "A Cheetah Can Get You Without Hitting Top Speed.")
A previous study done in the Masai Mara found that cheetahs would wait until tour groups broke for lunch before engaging in hunting behavior, Durant said.
Since Hetem and colleagues also found that the time of day had an effect on cheetah body temperatures, tourist schedules could affect a cat's core body temperature, Durant speculated. (Read about "Cheetahs on the Edge" in National Geographic magazine.)
If cheetahs in the Masai Mara are being forced to hunt at hotter times of the day, that might expose them to higher risks of heat stress, she said.
Source: NG
非常有趣的發現!
我一直以為過熱是原因.
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發表於 2013-7-26 12:42 PM
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