- Implantation of fertilized egg depends on female's body condition and environmental factors; occurs probably in November
- Gestation (conception to partuition) is relatively long: 195-265 days
- Pregnant females stay on land for 8 months, all the while food-deprived while they are in maternal dens, giving birth, raising cubs;
- Female's fat reserves are critical for survival of mother and cubs.
- Females loose up to 43 % of body weight during fasting
- 93% of the energy used for maintenance and reproduction come from body fat.
Females dig maternity dens
- Often on slopes of 20-40 degrees where snow is 1-3m deep.
- Temperature within may be 20 degrees warmer than outside.
- May be single chamber with short tunnels or complex system with several tunnels and chambers.
- Usually within 8 km of coast (rarely beyond 48 km).
Birth: Late November / early January; most births occur by mid-December.
- 2 cubs in approximately 70% of births; 3-cub births in about 6% of observations
- 4-cub litters reported but extremely rare