 Whales have evolved from land @-@ living mammals . As such they must breathe air regularly , though they can remain submerged for long periods . They have blowholes ( modified nostrils ) located on top of their heads , through which air is taken in and expelled in the form of vapour . They are warm @-@ blooded , and have a layer of fat , or blubber , under the skin . With streamlined fusiform bodies and two limbs that are modified into flippers , whales can travel at up to 20 knots , though they are not as flexible or agile as seals . Whales produce a great variety of vocalizations , notably the extended songs of the humpback whale . Although whales are widespread , most species prefer the colder waters of the Northern and Southern Hemispheres , and migrate to the equator to give birth . Species such as humpbacks and blue whales are capable of travelling thousands of miles without feeding . Males typically mate with multiple females every year , but females only mate every two to three years . Calves are typically born in the spring and summer months and females bear all the responsibility for raising them . Mothers of some species fast and nurse their young for a relatively long period of time . 
