Whales give birth to live young after a gestation period of between 10 and 18 months, depending on the species. They will give birth to one calf every three to five years. Although physically capable of birthing every year, this would expend far too much of the mother’s energy and she would soon become exhausted and unable to care for herself or her young. Twins are extremely rare, but have been known to occur. The newborn is usually about a quarter of the size of its mother. The calf will begin nursing within a few hours from birth and will continue for anywhere up to three years of age. They will continue to stick close to their mothers even after being weaned.
From weaning to sexual maturity is known as adolescence. This is the stage at which the two genders become clearly defined. Females will begin to explore areas and encounter whales outside of their pod but will stick close to their mother and the other females that assisted in their raising. The male juveniles will start to associate with other males of a similar age, forming juvenile and bachelor pods of their own. It is towards the end of this stage that they leave their mother’s pod completely and begin an independent life. They will start to search for sexually mature females at this stage, but will seldom be successful, since the females are far more likely to opt for mature bulls with which to mate.
Once a whale is sexually mature, it is considered to be an adult. Again depending on the species, this can be between six and 13 years of age. Females usually mature sexually at an earlier age than males. Once they reach this stage, they are ready to mate. This changes the focus of their existence somewhat. Where they were focussed almost exclusively on feeding and socialising, finding a mate and breeding becomes of major importance.
Males often become aggressive during the mating season, engaging in active displays of their power (breaching, lobtailing, etc...) as well as physically attacking other males that are vying for the attention of the available females. For this reason, there is frequently scarring on the flesh of the whale bulls.
Whales have a far longer life span than most other animals. These are the average life spans for some of the best known whales:
*The Blue Whale - 70 to 90 years
*The Bowhead Whale - 100 to 200 years
*The Humpback Whale - 40 to 100 years
*The Sperm Whale - 60 to 80 years
*The Beluga Whale - 40 to 60 years
*The Fin Whale - 60 to 100 years
*The Minke Whale - 30 to 50 years
*The Narwhal - 40 to 60 years