Half-pregnant grizzlies vital to species’ survival.

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Half-pregnant grizzlies vital to species’ survival

Expert explains fascinating world of grizzly bear reproduction

BY COLETTE DERWORIZ, CALGARY HERALD SEPTEMBER 11, 2012

Female grizzly bears in the Bow Valley reproduce later in life than most
bears and have cubs every three to eight years.

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 about 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 the Herald during
a recent visit to the park. “Those can be from three or four different
males as well, which is interesting.”

A healthy rate of reproduction is, of course, vital to 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 roughly 1,200 in the
1980s.

Studies suggest that in the Bow Valley, female bears begin reproducing
later in life than average and have cubs only 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 she’s tending to 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 out 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., escaped his nearly nine-
hectare 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 the bear’s first escape. “We just don’t know.

“It’s one of those mysteries.”

The same uncertainty 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 female bears who have bred 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 actually lead to more grizzly cubs.

“She needs to be around 24 per cent body fat to actually 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 actually
pregnant yet.”

In mid-November, the bears will make their way to dens and the blastocyst
will implant 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 born this year has been spotted this
summer by 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.

cder...@calgaryherald.com