Migrating mature males typically return to tropical waters in spring to breed with females. After mating, females have a gestation period of 14 to 16 months before giving birth to a single calf. Calves drink their mother’s milk for several years but also start eating solids, such as squid, in the first 12 months of their lives, according to the Norwegian Polar Institute.
Female sperm whales reach sexual maturity at 8 to 11 years old. Males may reach sexual maturity at about 10 years old, but they don’t reach a high enough social position to mate until they are in their 20s, according to ADW. Scientists don’t know the exact lifespan for sperm whales but evidence suggests the whales can live into their 70s, according to the Norwegian Polar Institute.
Sperm whales sleep for about 10 to 15 minutes at a time by diving down in the water, turning around, and napping in a vertical position with their tails down, while they slowly float back up towards the surface, Live Science previously reported. They only spend about 7% of their time in this inactive state, which is less time than any other mammal spends sleeping, according to a 2008 study published in the journal Current Biology, which was the first study to document this unusual sleeping behavior.