Penguins huddle together to keep warm as a way to shield their bodies from the full force of the cold weather experienced in Antarctica. While huddled, penguins exchange positions so that every colony member takes a turn at forming the outer perimeter, where exposure to the cold is greatest.
Penguins, in general, are well-suited for cold weather extremes with their array of dense, thin feathers that cover their bodies and provide ample insulation. By huddling tightly together, colonies of penguins can form a protective barrier whose only weakness is at the perimeter, where the cold has the greatest effect.
There are 17 species of penguins, but only four breed on Antarctica. These include the Adelie, Emperor, Chinstrap and Gentoo penguins. All four species exhibit the huddling behavior to keep warm on the Antarctic ice.
Size is an important advantage that the Adelie, Emperor, Chinstrap and Gentoo penguins have over the 13 other species. The larger size allows a greater surface area with which to shield their bodies from the extreme cold experienced in Antarctica. This also means that individual penguins can stand at the perimeter of the huddle for longer, which allows the next rotation of penguins more time to build up their body temperatures before going back out on the line.