Captured in Wapusk National Park in northern Manitoba, Canada, today"s image shows a polar bear mother and her cubs sharing a playful moment on the Arctic tundra. For polar bears, motherhood is a long and demanding commitment. Females give birth in winter, sheltering their newborn cubs in snow dens that provide vital insulation. Cubs are born tiny and rely entirely on their mother"s rich, fat-heavy milk for warmth and rapid growth.