Grizzly bears get ‘ half- pregnant’ after mating
Embryo isn’t implanted into uterine wall until mid- November, after a summer of binge eating
BANFF NATIONAL PARK — It’s often said you can’t be a little bit pregnant — unless you are a grizzly bear, that is.
From mid- May to early July, male and female grizzly bears mate.
If all goes well, the female grizzly gets “half- pregnant” for the summer, says Steve Michel, human/ wildlife conflict specialist with Banff National Park, where there are approximately 60 to 65 grizzly bears.
Essentially, the egg is fertilized and develops into a small embryo called a blastocyst. It then floats around the uterus for months before it implants.
“There can be multiple ones, which is usually the case,” says Michel, explaining the fascinating world of grizzly bear sex to Postmedia News during a recent visit to the park. “Those can be from three or four different males as well, which is interesting.”
Reproduction is an important part of the ongoing survival of grizzly bears in Alberta.
Grizzly bears were put on the province’s threatened list two years ago when it became clear the number of bears was declining. There are now about 700 grizzly bears in Alberta, compared with the 1,200 in the 1980s.
In the Bow Valley, studies suggest female bears begin reproducing later in life and only have cubs every three to eight years.
Take No. 64, a 23- year old female grizzly who has had multiple litters of cubs — including three yearling cubs right now that are expected to stay with her for at least three years.
“It’s extremely rare for us to have a bear that is in its mid- 20s and lived the entire time in the Bow Valley,” says Michel, noting she’s been dubbed the matriarch of the Bow Valley. “She’s a real success story.
“She’ll probably have one more set of cubs after this and that will probably be about it.”
No. 64 won’t mate again until the cubs go on their own.
Mating takes place in the late spring, when male bears travel long distances to find an available partner.
Boo, a male grizzly bear in captivity at Kicking Horse Resort after being orphaned when his mother was killed in B. C., has escaped his nearly ninehectare enclosure in 2005 after catching the scent of a lady. He was neutered, but escaped again in 2011 when a “gorgeous blond” showed up.
“Boo may have mated,” Craig Bolt, operations manager for the resort, says of his first escape. “We just don’t know. “It’s one of those mysteries.” The same holds true for Parks Canada experts who expect some of the female bears in Banff are “half- pregnant,” but won’t know for sure until they come out of hibernation next spring.
In a meantime, any bred bears will spend the summer gaining weight.
“In fact, that’s what she has to do,” explains Michel. “She has to get as fat as she possibly can over the summer otherwise she’s not going to have enough body fat on to be able to have an actual pregnancy and give birth to those cubs. There’s a threshold there.”
So, a good buffalo berry season can lead in more grizzly cubs.
“She needs to be around 24- per- cent body fat to have a successful gestation period,” he says, referring to studies that have looked at the issue. “So she eats all summer, she doesn’t have to worry about morning sickness or any of that stuff, because she isn’t pregnant yet.”
In mid- November, the bears will make their way to the dens and the blastocyst implants in the uterine wall, making the bear pregnant.
“Then, it’s just like a normal pregnancy, but it’s quite short,” Michel explains. “She literally goes to sleep and becomes pregnant about the same time she puts her head down in her bed.”
Halfway through the six- month hibernation, she gives birth to the cubs ( usually between one and three) and immediately starts nursing.
“They are really tiny, they are only the size of a squirrel,” he says. “They weigh about half a pound when they are first born.
“Then about three months later they all leave the den together. By that point, they are a decent size.”
Only one mother grizzly with cubs of the year has been spotted this summer on a remote camera in the backcountry, but there are at least half a dozen bears with one- year old or two- year old cubs in Banff National Park.