Washington - The fastest land animal on Earth depends on more than speed to catch its prey. In order to successfully hunt, cheetahs need to be able to slam on the brakes and turn quickly, according to new research. One of the first efforts to capture the biomechanics of how animals hunt in the wild, the study pushes the limits of how researchers monitor animals.
“It's going to allow us for the first time to understand what any species is doing in its stride-by-stride activity,” says David Carrier, a comparative biomechanist at the University of Utah in Salt Lake City who was not involved in the work. “This is a big step forward in terms of understanding what animals do in the real world.”
Captive cheetahs have been clocked at more than 100 kilometres per hour, as fast as many cars on the highway. But how do they perform on African savannas? To find out, biomechanist Alan Wilson of the Royal Veterinary College in London and his colleagues spent 10 years perfecting a radio collar equipped with GPS, as well as gyroscopes, magnetometers, and accelerometers for detecting when a cheetah speeds up, slows down, or turns. The collars incorporated solar batteries, as well as a nonrechargeable backup battery, and, for part of the experiment, were programmed to turn on only when a cheetah started to run during times of the day when it was known to hunt. These features all extended the life of the collar to at least a year, enabling the collection of an unprecedented amount of data about each animal.
When activated, the collar records the animal's position, velocity, and direction it's heading up to 300 times a second and relays that data via radio signals to the researchers. Three female and two male cheetahs wore these collars for 18 months, during which 367 hunting “runs” were recorded.
Wilson says that he was surprised how slowly cheetahs went during a hunting run, for example. The fastest hit 106 kilometres per hour, but much of the time the animals topped out at about 60 percent that speed and maintained that pace for just 1 or 2 seconds as they ran down impala. Instead, hunting success depended on the cheetah's ability to outmaneuver the prey. By slowing down by 4 meters per second in a single stride, the cat could reach its target and then quickly decrease its speed to make sharp turns. The rate of speed up and slow down was double that of polo horses, and they accelerated with four times the power of the fastest human sprinters, Wilson and his colleagues reported online Wednesday in Nature. They observed, based on downtime recorded after a hunt, that even with this prowess, the cheetah brings down an impala or other game about only one in four tries.
Challenging conventional wisdom, the data also revealed that cheetahs don't restrict their hunting to open grassland or to dawn or early mornings. About half the time they hunted in the open, but about a quarter of the time, they were among shrubs and large trees, and sometimes they even hunted in dense vegetation. Hunting took place during the day as well as at dawn. “What they found out about cheetahs is not what we thought,” Carrier notes.
He and other researchers are impressed with the quantity and detail of the information that Wilson was able to collect. “It's the life and death struggle of the speedsters of the savanna,” says Thomas Roberts, a biomechanist at Brown University. “And it is all recorded digitally, live, with technology that allows you to watch the animal's path on a Google map. This kind of technology has the potential to transform our understanding of animal behaviour” and better plan conservation and management of animals.
Having day-in and day-out data for individual animals over months “is such a giant leap forward,” Carrier says. “During my career, we've always had information from lab studies and anecdotal accounts of what's happening in the real world,” that sometimes didn't turn out to be correct. But the collars collected enough information that Wilson and his colleagues could quantify the different behaviours. Carrier hopes to see other species studied this way, including prey. Wilson is now following lions, wild dogs, and even domestic cats with these collars. - Washington Post
* This is adapted from ScienceNOW, the online daily news service of the journal Science. http://news.sciencemag.org