Dr Jon Aars from the Norwegian Polar Institute in Tromso describes what happened in the journal Polar Biology. On the
Holidaying in the wildlife hotspot of Duvefjorden, Nordaustlandet, Mrs Plumb spotted the mother bear with a seven-month-old cub hitching a ride on her back.
"The cub was on the back of the polar bear when it was in the water, then it got out of the water and stayed on its mother's back a little, then she shook it off," Mrs Plumb explains.
For large parts of the year, polar bears ( Ursus maritimus ) live among the sea ice, feeding mainly on seals. The challenge for the bears is to navigate the many areas of open water between the islands of floating ice.
Seeing the bear had a radio collar, Mrs Plumb got in touch with Dr Aars to report her sighting and asked if this was a common behaviour. "I hadn't seen this behaviour before or heard about it so I asked other researchers and found out it is something that has been observed but not frequently at all," Dr Aars says.
Out of the cold
Cubs are known to ride their mother's back when moving through deep snow as they leave their den areas. Cubs of other bear species such as the sloth bear also ride on their parents. However, the the extent to which polar bear cubs hitch a ride on swimming adults in open water is unknown. Dr Aars was especially interested if this behaviour might have some adaptive value for the bears. "This could be potentially important because it means that the cubs get exposed to less water. If they are in the water they would have to swim and very small cubs are very badly insulated in water," he says.
Adults are well adapted to swimming in the cold water with insulating subcutaneous fat and and large body mass. However, young bears have very little insulating fat, as they do not develop brown fat stores until adulthood. Their fur coat also loses most of its insulating properties if immersed in ice water. Dr Aars suggests staying out of the water could be vital for the cub's ability to survive in habitats where sea ice is scattered across open ocean.
Speedy transport
Another reason for the behaviour could be that it aids the mother's mobility in the water. "I would imagine a big benefit is the ride is faster, an adult female polar bear is a strong swimmer, cubs of this size are much slower and time in water is time lost hunting," suggests Professor Andrew Derocher from the
The scientists are interested to find out if this behaviour might be a regular occurrence within the polar bear population. "It's important to remember the vast areas it may happen in. It has not been observed that much, but it could be more common than we think," says Dr Aars.
Prof Derocher also wonders if the people who share the bears' habitat might be able to help unravel this behaviour.
"It would be interesting to hear if Inuit have seen this behaviour, I'm always very impressed that our observations match what local people have seen before, but they don't tell you about them unless you ask."
Story from BBC NEWS:
http://news.bbc.co.uk/go/pr/fr/-/earth/hi/earth_news/newsid_8284000/8284906.stm
Published: 2009/10/02
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Spotted hyenas may not be smarter than chimpanzees, but a new study shows that they outperform the primates on cooperative problem-solving tests. (Credit: Image courtesy of Duke University)Captive pairs of spotted hyenas (Crocuta crocuta) that needed to tug two ropes in unison to earn a food reward cooperated successfully and learned the maneuvers quickly with no training. Experienced hyenas even helped inexperienced partners do the trick.
When confronted with a similar task, chimpanzees and other primates often require extensive training and cooperation between individuals may not be easy, said Christine Drea, an evolutionary anthropologist at Duke University.
Drea's research, published online in the October issue of Animal Behavior, shows that social carnivores like spotted hyenas that hunt in packs may be good models for investigating cooperative problem solving and the evolution of social intelligence. She performed these experiments in the mid-1990s but struggled to find a journal that was interested in non-primate social cognition.
"No one wanted anything but primate cognition studies back then," Drea said. "But what this study shows is that spotted hyenas are more adept at these sorts of cooperation and problem-solving studies in the lab than chimps are. There is a natural parallel of working together for food in the laboratory and group hunting in the wild."
Drea and co-author Allisa N. Carter of the Univ. of California at Berkeley, designed a series of food-reward tasks that modeled group hunting strategies in order to single out the cognitive aspects of cooperative problem solving. They selected spotted hyenas to see whether a species' performance in the tests might be linked to their feeding ecology in the wild.
Spotted hyena pairs at the Field Station for the Study of Behavior, Ecology and Reproduction in Berkeley, Calif. were brought into a large pen where they were confronted with a choice between two identical platforms 10 feet above the ground. Two ropes dangled from each platform. When both ropes on a platform were pulled down hard in unison -- a similar action to bringing down large prey -- a trap door opened and spilled bone chips and a sticky meatball. The double-rope design prevented a hyena from solving the task alone, and the choice between two platforms ensured that a pair would not solve either task by chance.
The first experiment sought to determine if three pairs of captive hyenas could solve the task without training. "The first pair walked in to the pen and figured it out in less than two minutes," Drea said. "My jaw literally dropped."
Drea and Carter studied the actions of 13 combinations of hyena pairs and found that they synchronized their timing on the ropes, revealing that the animals understood the ropes must be tugged in unison. They also showed that they understood both ropes had to be on the same platform. After an animal was experienced, the number of times it pulled on a rope without its partner present dropped sharply, indicating the animal understood its partner's role.
"One thing that was different about the captive hyena's behavior was that these problems were solved largely in silence," Drea said. Their non-verbal communication included matching gazes and following one another. "In the wild, they use a vocalization called a whoop when they are hunting together."
In the second and third experiments, Drea found that social factors affected the hyenas' performance in both positive and negative ways. When an audience of extra hyenas was present, experienced animals solved the task faster. But when dominant animals were paired, they performed poorly, even if they had been successful in previous trials with a subordinate partner.
"When the dominant females were paired, they didn't play nicely together," Drea said. "Their aggression toward each other led to a failure to cooperate."
When a naïve animal unfamiliar with the feeding platforms was paired with a dominant, experienced animal, the dominant animals switched social roles and submissively followed the lower-ranking, naïve animal. Once the naïve animal became experienced, they switched back.
Both the audience and the role-switching trials revealed that spotted hyenas self-adjust their behavior based upon social context.
It was not a big surprise that the animals were strongly inclined to help each other obtain food, said Kay Holekamp, a professor of zoology at Michigan State University who studies the behavioral ecology of spotted hyenas.
"But I did find it somewhat surprising that the hyenas' performance was socially modulated by both party size and pair membership," Holekamp said. "And I found it particularly intriguing that the animals were sensitive to the naïveté of their potential collaborators."
Researchers have focused on primates for decades with an assumption that higher cognitive functioning in large-brained animals should enable organized teamwork. But Drea's study demonstrates that social carnivores, including dogs, may be very good at cooperative problem solving, even though their brains are comparatively smaller.
"I'm not saying that spotted hyenas are smarter than chimps," Drea said. "I'm saying that these experiments show that they are more hard-wired for social cooperation than chimpanzees."
Journal reference:
Grauer's gorilla
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