Individual variation in the duration of pregnancy and birth date in Antarctic fur seals: The role of environment, age, and sex of fetus

The duration of 506 pregnancies in Antarctic fur seals (Arctocephalus gazella) was measured 1983-1993. On average, pregnancy lasted 359 days, with a range of 340-390 days, representing 20% of the period of post-implantation fetal growth. Pregnancy was longest and birth dates latest in years associated with reduced availability of food. Sex of fetus and birth mass had no effect on the duration of pregnancy or date of birth. However, dates of parturition tended to be consistent within individuals.