Whales are mammals, so they breathe air at the surface and nurse their young with milk.

The longer version

Air-breathing ancestors left whales with lungs rather than gills, so they must surface regularly, exhaling through a blowhole set on top of the head so almost nothing needs to be lifted clear of the water. Exchange takes seconds.

Warm-blooded metabolism demands steady oxygen, and calves are born alive underwater, reaching the surface quickly for their first breath. Their milk is extremely rich in fat, letting a young animal build insulating blubber fast in cold water. Hair survives only as traces, while that thick blubber handles warmth, buoyancy and stored energy. Blubber also lets these animals dive deeply and cross whole oceans between feeding grounds.

Where this entry sits

Oceans and Sea Life looks at the salt water that covers most of the planet, from crashing waves and tides to the darkest deep-sea trenches. Expect notes on coral, fish, whales, sharks, jellyfish, shells, and the strange creatures that live far below the surface. The full list sits on the Oceans and Sea Life page, where every entry is listed in order.