Whales are mammals, so they produce milk. In order for an organism to be classified as a mammal, it must have certain physiological features, and feeding their young with milk is one requirement. Whales also have lungs, are warm blooded and have a fine layer of hair.
Female whales have a gestation period of 9 to 15 months. During this time, they begin to produce milk in their mammary glands. At the end of pregnancy, whales give birth to a live calf. Sometimes twins are born. The calves rely upon the nutrients of their mother's milk for over one year.