 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 . To feed the new @-@ born , whales , being aquatic , must squirt the milk into the mouth of the calf . Being mammals , they , of course , have mammary glands used for nursing calves ; they are weaned off 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 . Females deliver a single calf with gestation lasting about a year , dependency until one to two years , and maturity around seven to ten years , all varying between the species . This mode of reproduction produces few offspring , but increases the survival probability of each one . Females , referred to as " cows " , carry the responsibility of childcare as males , referred to as " bulls " , play no part in raising calves . 
