 Females become fertile at around 9 years of age . The oldest pregnant female ever recorded was 41 years old . Gestation requires 14 to 16 months , producing a single calf . Sexually mature females give birth once every 4 to 20 years ( pregnancy rates were higher during the whaling era ) . Birth is a social event , as the mother and calf need others to protect them from predators . The other adults may jostle and bite the newborn in its first hours . 
