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Eastern Slopes Grizzly Bear Project

Mating

When it’s springtime in the Rockies, grizzly bears begin their mating rituals. The whole mating process starts in mid-May to mid-June. From afar, scientists have watched grizzly bear courtship and copulation in the wild. They believe that in springtime, females leave scent trails for wandering males to follow. Such trails may be the key to finding a female bear in areas where grizzly populations are at very low densities. Such is the case in the Central Rockies Ecosystem where there is only 1 bear for every 50 to 100 sq. km. When a male finds a female, the process of getting to know one another begins. At any other time of the year, grizzly bears are solitary creatures that will avoid close encounters with other bears, especially large adult males. During mating season, however, solitary bears let down their guard a little although not for long.

Not surprisingly, male and female grizzly bears usually spend at least a few days testing one another before mating occurs. This type of interaction is important when getting to know an animal that is strong enough to injure or even kill you. The two bears may chase each other, play fight or even nuzzle and lick each other once they are aquainted. The outcome of this process may be rejection or the formation of a pair bond that lasts from several days to a couple of weeks.

In Banff and Waterton Lakes National Parks, researchers have observed an amazing mating ritual. Male grizzly bears have been seen “herding” females onto mountain tops. In doing so, a male is able to isolate a female so that her scent does not attract other bears. In Banff National Park, a male bear kept a female confined within a 2 to 3 hectare mating area for 13 days. On occasion, the female bear tried to escape but the persistent male cut her off and sent her back up the ridge.

At first, a male’s approaches are rejected by the female with paw swats, charges or bites. Eventually, repeated copulation occurs over a few days. The adult male is 1.5-2.0 times larger than the female and mounts her from the rear. At first, copulation may last a few minutes but there may be several bouts that last up to one hour.

Shortly after these prolonged copulations, the male and female separate. The female will likely become pregnant but this does not necessarily mean she will have cubs the following spring. Grizzly bears have developed a process called delayed implantation. At first, the embryo floats freely in the female bear’s uterus and its development is delayed. Sometime in the fall, the female’s body senses whether she will be able to store enough fat reserves to support herself and her cub over the winter. If she can, the embryo is implanted in the uterine wall and it begins to grow. If her energy stores are low, the embryo is reabsorbed by her body and she will not give birth to cubs the following spring.

After mating, the male grizzly bear has no further association with the female. The female may mate with other males but the period of reproductive readiness is brief. If she does mate again, and her fat stores are adequate, she may even give birth to several cubs from different fathers. This explains why cubs from the same litter can look very different from one another. In about 1.5 to 4.5 years, the cubs will leave their mother’s side. At this time the female grizzly bear is free to embark on the whole mating ritual again.

Suggested specific readings:

Herrero, Stephen, and David Hamer. 1977. Courtship and copulation of a pair of grizzly bears, with comments on reproductive plasticity and strategy. J. Mammal. 58(3): 441-444.

Hamer, David, and Stephen Herrero. 1990. Courtship and use of mating areas by grizzly bears in the Front Ranges of Banff National Park, Alberta. Can. J. Zool. 68(12): 2695-2697.