Editing Whale (section)

=== Life cycle ===
{{See also|Right whale#Courtship and reproduction}}

Whales are fully aquatic creatures, which means that birth and courtship behaviours are very different from terrestrial and semi-aquatic creatures. Since they are unable to go onto land to calve, they deliver the baby with the fetus positioned for tail-first delivery. This prevents the baby from drowning either upon or during delivery.

[[File:Southern right whale4.jpg|thumb|upright|A [[southern right whale]] tail-sailing]]
To feed the newborn, whales, being aquatic, must squirt the milk into the mouth of the calf. Nursing can occur while the mother whale is in the vertical or horizontal position. While nursing in the vertical position, a mother whale may sometimes rest with her tail flukes remaining stationary above the water. This position with the flukes above the water is known as "whale-tail-sailing." Not all whale-tail-sailing includes nursing of the young, as whales have also been observed tail-sailing while no calves were present.{{sfn|Higgs|2023}}

Being mammals, they have mammary glands used for nursing calves; weaning occurs at about 11 months of age. This milk contains high amounts of fat which is meant to hasten the development of blubber; it contains so much fat that it has the consistency of toothpaste.{{sfn|Modern Marvels|2007}} Like humans, female whales typically deliver a single offspring. Whales have a typical gestation period of 12 months. Once born, the absolute dependency of the calf upon the mother lasts from one to two years. Sexual maturity is achieved at around seven to ten years of age. The length of the developmental phases of a whale's early life varies between different whale species.{{sfn|Johnson|Wolman|1984}}

As with humans, the whale [[R/K selection theory|mode of reproduction]] typically produces but one offspring approximately once each year. While whales have fewer offspring over time than most species, the probability of survival for each calf is also greater than for most other species. Female whales are referred to as "cows." Cows assume full responsibility for the care and training of their young. Male whales, referred to as "bulls," typically play no role in the process of calf-rearing.

Most baleen whales reside at the poles. To prevent the unborn baleen whale calves from dying of frostbite, the baleen mother must migrate to warmer calving/mating grounds. They will then stay there for a matter of months until the calf has developed enough blubber to survive the bitter temperatures of the poles. Until then, the baleen calves will feed on the mother's fatty milk.{{sfn|Zerbini et al.|2006}}

With the exception of the humpback whale, it is largely unknown when whales migrate. Most will travel from the Arctic or Antarctic into the [[tropics]] to mate, calve, and raise their young during the winter and spring; they will migrate back to the poles in the warmer summer months so the calf can continue growing while the mother can continue eating, as they fast in the breeding grounds. One exception to this is the [[southern right whale]], which migrates to [[Patagonia]] and western New Zealand to calve; both are well out of the tropic zone.{{sfn|Kennedy|2008|p=966}}