Sex in the forest:
Researching the sex life of bears
If you are walking in the woods and encounter a large male bear, you have little to fear as a human. If you were a cuddly bear cub, however, he would likely kill you, say researchers.
Andreas Zedrosser with one of the bears fitted with GPS. (Photo: Sven Brunberg)
Nearly half of all bear cubs born in Norway and Sweden are killed in their youth - almost always by a male bear that wants to mate with the mother.
In the realm of bears, the struggle to spread one's own genes leaves many victims in its wake.
Researchers involved in the Scandinavian Brown Bear Project now aim to learn more about the explosive, dramatic sex life of bears.
Researchers have fitted GPS transmitters to 36 adult bears, both males and females; the scientists receive text-message transmissions every 10 minutes as to the bears' location and which other bears they meet - and mate with.
Battle of the sexes
Andreas Zedrosser, an Austrian post-doctoral fellow at the Norwegian University of Life Sciences (UMB) in Ås, receives funding for his part in the bear project from both the Research Council of Norway and its Austrian counterpart, the Austrian Council for Research and Technology Development. Dr Zedrosser's objective is to find out more about ursine reproductive strategies.
"It's a battle of the sexes fought in the woods. For the male, everything revolves around propagating his own genes. For the female, it's all about the survival of her cubs. While he uses murder as a strategy, she applies her own adaptive method: behaving as promiscuously as possible during the mating season."
By mating with multiple males, explains Dr Zedrosser, female bears ensure that many litters (nearly 30 per cent) have more than one father. Since the male is loathe to kill his own offspring, uncertainty about paternity is a good female strategy.
Collecting scent samples
Andreas Zedrosser and veterinarian Knut Madslien measuring the body fat ratio of a large male brown bear. (Photo: Sven Brunberg)
In order to prevent the death of his progeny, a male will protect within his territory any female with his offspring. But how does a male bear remember which females he mated with a year ago?
This is one of the mysteries that bear researchers are now attempting to unravel. Does he remember her, and does this enable him to know which cubs are his? Or does he perhaps recognise his progeny by their scent? Researchers have collected scent samples from many bears, but research into this phenomenon is still in its infancy.
Researchers have discovered that bears have a gland, next to the anus, that secretes what is most likely a territorial marking scent. Chemical analyses of this secretion may divulge how these animals communicate. One master's and one doctoral degree are being completed on exactly this topic, adds the Austrian researcher.
Hunters' kills provide opportunities
Now and then a large male bear is shot by hunters. Then the other males, sensing their opening to take over the dead bear's females, will begin getting rid of his offspring. This behaviour is not a matter of propagating the species per se, but rather the opportunistic passing on of one's own genes.
"When a mother emerges from her den with her cubs in late April or early May, she knows she needs to tread carefully in the evenings, when males are most active. She hides with her offspring; if she is unlucky, a male will find them and kill her cubs. Then he will pursue the mother in order to impregnate her." After only a day or two, says Dr Zedrosser, the two will mate.
Major bear project
The population dynamics of large predators is in all probability quite distinct from those of other large mammals. The killing of young offspring in order to mate with their mother had been seen before in lions, primates, and other animals. But until the Scandinavian Brown Bear Project, this behaviour had never been discovered in non-social animals, i.e. animals that do not live in families or groups.
Running since 1984, the project is the world's most comprehensive study of bears. In all, some 1,317 markings have been carried out on 550 different individuals.
When the project began, little was known about the bear's ecology or behaviour. The knowledge gleaned over the course of the past 20 years has spawned seven completed doctoral degrees with eight more in progress, plus an even greater number of master's degrees as well as a variety of published scientific papers, including in the prominent journals Science and Nature.
Dangerous to humans?
We now know far more about the Scandinavian brown bear's diet and roaming habits. We are also learning more and more about other aspects of bear behaviour. Our understanding has grown considerably in terms of population dynamics and how this is influenced by hunting. Researchers have also learned the answer to the most common question posed about the bear: Is it dangerous to people?
On the whole, the answer is "no". The Scandinavian brown bear is not dangerous to people except in certain specific situations. Researchers base much of this conclusion on a project that studied episodes of people encountering bears, an event that occurs more often than people may like to imagine. The bear notices us, although we are seldom aware of the bear when enjoying the woods. As the Scandinavian research has revealed, even at a distance of just 50-100 meters from a bear, people detect the bear in only one of ten cases.
But you can be quite certain the bear is aware of you. However, researchers have found that in the vast majority of cases when a bear senses people approaching, the animal will simply lie down and hide, or sneak off unnoticed.
Scandinavians encountering bears more frequently
Knowledge about bear behaviour is useful, especially in countries such as Sweden, where the bear population has grown rapidly in recent years.
Last year some encounters with bears ended in human casualties. Although it is rare for people to be injured or killed by bears, it can happen.
If you come across a mother with her cubs in tow, or disturb a bear while it is eating some delicacy, the bear can become agitated. Dogs can also greatly irritate bears, which probably explains why it is almost exclusively hunters who have the especially unpleasant bear encounters.
Today's Scandinavian brown bear population is estimated to number at least 2,600. With so many bears, encounters between them and humans are getting more and more frequent. Sweden is home to the greatest number of bears in Scandinavia, but the bear's long-distance roaming habits make it very difficult to distinguish between Norwegian and Swedish bears. We know that at least 126 bears have lived in or roamed into Norway's forests recently.
- Published:
- 15.09.2008
- Last updated:
- 16.09.2008
