Penguins are a group of aquatic, flightless birds living almost exclusively in the Southern Hemisphere, especially in Antarctica. Highly adapted for life in the water, penguins have counter shaded dark and white plumage, and their wings have evolved into flippers. Most penguins feed on krill, fish, squid and other forms of sea life caught while swimming underwater. They spend about half of their lives on land and half in the oceans.