| Polar
Bears of Churchill - Mothers and Cubs
The reproductive process of a female polar bear is one of the most
incredible achievements of any animal on this planet. It begins as
receptive females enter estrous (reproductive state) and mate out
on the ice in late April or early May.
Mating lasts for several days and, during this time, the male must
fend off several competitors, provided he has not steered the
female to their own private spot! This prolonged period of mating
may be an adaptation aimed at ensuring that the largest and most
capable male bears are most likely to mate. This would, thereby,
improve the likelihood of cub survival.
Testosterone is running highest at this time of year. While the
male is quite gentle almost suave in his courtship, copulation is a
different story, occasionally resulting in a broken bacculum (the
polar bear’s penis bone). Ouch!
Of course, if a male cannot fend off his competition for the
duration of the process, cubs born in the same litter, may not
necessarily have the same father.
While the egg has been fertilized by mid-May, the pregnancy
does not begin for another four months. This is the result of an
adaptation called delayed implantation. Unless the female has
maintained a minimum weight of 300kg (660lbs) by September,
the egg will simply be reabsorbed.
She needs these excess fat stores, as from mid-July through to
the following February, she will have little or no access to food.
During this time, she will move inland, prepare a maternity den,
give birth, nurse her young and, in late winter, lead them to the
coast. Once there, she must seek out seal birthing lairs and break
into them, sometimes through one metre (3’) of snow, to both
feed herself and her cubs. Only then, does she begin two years of
feeding, protecting and teaching her cubs.
Motherhood starts in mid-September with pregnant females nestled
into an earthen maternity den and the three month pregnancy
just beginning. Near Churchill, cubs are born in early to mid-
December once the den has become covered and insulated by a
layer of snow.
Less than one kilogram (2.2 lbs) at birth, they are blind, lightly
furred and utterly helpless. While the den remains fairly
comfortable, close to 0C (32F), up to thirty or forty degrees
warmer than temperatures outside, she will also use her breath and
body heat to keep her cubs warm.
Inside the den, the female does not eat or drink, her body absorbing
its waste. From a normal rate of 70 beats per minute, her heart
rate drops as low as eight beats per minute. It is in this state that
she gives birth and even nurses. The cubs grow quickly, thriving
on mother’s high fat, high protein milk. Weighing around 9-14kg
(20-30 lbs), they emerge from the den between late February and
mid-March.
After spending a week or so acclimating to the temperatures and
exercising, they begin the journey to the sea ice. With most dens
30-50km (20-30 miles) inland, this is no small feat for a little polar
bear. Many do not make it. There seems to be less than a 50%
chance of survival through the first year of life, overall. Naturally,
first time mothers (about five years of age) lose the majority of
their cubs while older, stronger, smarter females are much more
successful in raising their young. The chances of survival for
polar bear cubs increase with the age of the mother, generally up to
about fifteen years of age.
Spring is a critical time of year for mothers and cubs. The females
energy is taxed by milk production and the fact that she has not
eaten for up to eight or nine months, one of the longest fasting
periods for any mammal.
In this tender state, she must guide her cubs to the coast and the
seal birthing lairs. As well, the polar bears of Churchill are one of
the few populations with active predators, some cubs are taken by
the resident wolf population. The pack may work to separate the
mother from one or both of her cubs.
Young mothers rarely succeed in this journey, some even abandon
their cubs along the way. Older, more experienced bears, however,
have a much better chance of success. They generally show an
incredible bond with their young, exhibiting patience and care.
Through deep snow or difficult terrain, a female may even let the
cubs climb on her back, to rest as she carries them to the ice.
The incredible challenges associated with pregnancy and
motherhood means that this group of bears are most likely to be
negatively affected by the fluctuating weather and ice patterns
associated with climate change. Remember, females need to
maintain at least 200kg (440lbs) of fat reserves for their pregnancy
to initiate. Without a good spring hunt, the egg will simply be
reabsorbed. If this hunting season is reduced significantly, it could
mean that overall cub production will be reduced to the point
where it does not offset the mortality rate.
Teaching and Learning Behaviour
Mothers with cubs again present some of the most interesting
moments in bear season. She is in almost constant communication
with her cubs whether they are listening or not.
Presented by an uncertain situation or threatening bear, she often
keeps her cubs behind her, leaving them sitting together until she
has assessed the potential danger. Ever alert, she not only uses
body language but may also smack her lips, huff and even growl
at her cubs. Often, one sound from her and her otherwise carefree
cubs come running to her side. Some mothers are very disciplined,
keeping a ‘tight leash’ on their cubs, others let their young ones
roam, sometimes even a little too far…
The cubs, for their part, watch their mother intently, often
mimicking her behaviours and her movements. During ‘bear
season’, cubs of older, confident bears, sometimes even team up
to drive away other bears. With their front lip extended, they have
been seen charging at bears well over 200kg (400lbs) heavier. Of
course, it does not hurt that mom is standing right behind her cubs.
While females stay away from males as a general rule, it is a rare
male that will attack a mother defending her cubs. Most know, that
it is a battle that they will not likely leave unscarred. However,
with occasional cases of cannibalization recorded amongst bears,
females usually choose discretion over valour.
Cubs will stay with their mother for two or three years learning
how to hunt and how to survive. These first years are critical
to these bears’ life path. The female’s actions and patterns will
impact her cubs and their behaviours for much of their life.
Studies have shown that cubs encountered near Churchill or at the
former garbage dump site had a high percentage of returning in
later life to become problem bears. Since females prefer to return
to familiar areas, young females were more likely to return and
bring successive generations to the site
Nursing
Witnessing a mother polar bear nursing her cubs is one of the best
moments of any bear season. Female polar bears nurse their cubs
for approximately two years. In the first months, their milk is rich
in protein and comprised of over 30% fat content. While this fat
content declines over time, the cubs grow quickly.
First year cubs, also known as COYs (Cubs of the Year), generally
nurse for five or ten minutes every few hours. Often, they will start
nudging their mother to signal their hunger. Some even vocalize
their opinion with a loud, nagging bray.
Females nurse from a sitting position. In preparation, they will fix
a day bed, either amidst the kelp or along the edge of a snowdrift.
The cubs will sit and watch as mother digs and packs down her ‘chair’, not unlike the way a dog ‘nests’ before laying down. Once
she settles into position, the cubs waste no time nestling into her
lap to begin nursing.
Her movements become very fluid and very gentle. She nudges
her young as they quietly coo and purr while suckling. Sometimes,
she will lift her head, stretching her neck in an elegant curve.
Eventually, she lays down on her side signaling the end of the
session. Of course, if one cub, usually the male, gets a little too
assertive, nursing can end abruptly, her gentleness quickly turning
into a hard cuff, sending her cub rolling away!
It is extremely important for polar bear watchers to remain quiet
and respectful during this rare opportunity. The female must feel
comfortable through the entire process from preparation of the
daybed to her final stretch; any distractions may make her nervous
enough to get up and cut meal time short, leaving everybody, both
tourists and cubs, more than a little disappointed...
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