Thick layers of fat keep penguins warm in the cold water. Penguins eat fish. They spend much of their lives in water, but lay eggs and raise their young on land. They make their nest in enormous colonies called rookeries . One rookery may have as many as a million penguins.
Most species make their nests on bare ground or in the grass.
They scrape shallow hollows in the dirt and lay their eggs. A few species lay eggs in tunnels dug in the ground. The female emperor penguin leaves the ocean at the start of the Antarctic autumn. She lays a single egg on the bare ice, and immediately returns to the water. The male then cares for the egg until it hatches.