AGE-SPECIFIC REPRODUCTIVE-PERFORMANCE OF FEMALE POLAR BEARS (URSUS-MARITIMUS)

Age-specific patterns of maternal Weight, litter size, litter weight a nd reproductive effort were investigated for polar bears (Ursus mariti mus) from western Hudson Bay. Most relationships were described by qua dratic equations. Maternal weight in spring and autumn increased until 17 and 15 years of age, respectively, and then declined. Age-related increases in maternal weight were thought to be associated with improv ing hunting skills. The relationships between age and litter size, lit ter weight and reproductive effort, in both the spring and autumn, inc reased until 14 to 16 years, followed by a decline. We speculate that age-related decreases in reproductive performance are due to undetermi ned processes associated with ageing that impair the accumulation of f at stores necessary for reproduction. Pregnant females lost an average of 127 kg overwinter which represented an average of 43.5% of their a utumn weight. Fat stores remaining after the overwinter fast may be cr itical for maintaining an energy supply to cubs once they return to th e sea ice where the distribution and abundance of their prey is unpred ictable. We suggest that maternal condition is an important factor con tributing to lifetime reproductive success in polar bears.