Well, I’m sick of polar bear politics for a while… and its only seven days until International Polar Bear Day, whatever that is… so for the next seven days, I’m just writing about bears and Churchill stories.
Watchee Lodge has just opened for business. This is the mother and cubs viewing lodge in Wapusk National Park. Its actually a refurbished outpost from the Churchill Rocket Range days. It used to host high-end photographers and film-makers but now its a bit more touristy, with french and japanese clients kicking off the season (for polar bears and northern lights). Here about twenty or so clients travel in custom track vans and watch for mothers and cubs to emerge from the maternity den.
The maternity denning story itself is pretty interesting. Pregnant females will begin denning up in September or October, first burrowing (if a bear can burrow) into the peat banks on the lee side of the many lakes and creeks south of Churchill.
They do this mainly because the snow cover in early winter is highly variable and snow dens are simply not available. Snow builds up in these spots first and by mid-November, the dens are about half-peat and half-snow, both providing insulation from temperatures that reached -40 and beyond this winter.
Denning on land for polar bears is highly preferable to denning on the sea ice. The survival rate of cubs appear to be a fair bit higher. It appears that most polar bears that den on multi-year pack ice quite likely moved out there from hunting or development pressures on land.
Inside a den, you can find various scratchings on the permafrost inside the den. This is basically annual maintenance. The ‘maternity denning chamber’ is around 1.5-2m (5′-6′) wide and about 1-2 M long (3′-6′), maybe about 1m (3′) high. Needless to say, its pretty snug. Extending from this there is about a 1m (3′-4′) tunnel, sometime made of snow, sometimes peat. It has a downward slope so that warm air is also trapped in the denning chamber. Studies have shown that the chamber remains just below freezing (0C/32F) through the winter. Pretty amazing when you think about it.
The opening gets ‘sealed’ with snow making it challenging to locate dens. Usually they are found by the small breathing hole or signs of air coming out. Snow is fairly porous so the bears are fine inside the den – with, of course, occasional maintenance through the winter. While not ‘truly’ hibernating, the mother’s heartbeat can drop from around 70 beats per minute down as low as eight bpm in the den.
Cubs along western Hudson Bay are generally born around Christmas although the range can extend from late November to January. It ‘seems’ that cub birthing times have actually shifted a week or two back over the years, not sure if this has been proven yet though.
Two cubs are still the norm, sometimes one if the ice season has been poor or the mother is very young or very old. And, yes, triplets, though never common, are still encountered. The cubs are about 25cm (6″ long) at birth and weigh about 1kg (2lbs).
They grow quickly in the den. At this time, the mother’s milk is about 30% fat content (although this will decline through the coming year). By the time they emerge (now), they will weigh about 9-14kg (20-30lbs). Their fur is still not thick enough to insulate them from the cold so severe cold or immersion in water are serious threats.
Most dens are 30-50km from the coast and, most importantly, the locations of seal birthing dens, critical to the survival of cubs. On this journey, the female must avoid predators such as wolves and sometimes wolverines that will attempt to separate a cub. If need be, the female will even resort to carrying her cubs on her back for much of this journey.
It is believed that the Wapusk National Park denning area produces 200-300 cubs in a season, however, survival rate is only about 50%. The exciting news this year is the maternity denning area ‘discovered’ down by Nanuk Lodge and York Factory. While rumoured for many years, it appears to cover a fairly large area. Is it possible that western Hudson Bay population is producing 300-400 cubs per year? Sounds good to me.