Puffins and penguins
Although puffins (left) and penguins (right) share similar coloring and diet, penguins belong to the family Spheniscidae, while puffins belong to the family Alcidae. The most obvious difference is that penguins don't fly. They have solid bones, which makes them better swimmers. Puffins, like most birds, have hollow bones so that they aren't weighed down in flight. Puffins are generally smaller, ranging in size from 10 to 15 inches, while penguins can be as tall as 4 feet. Location makes a difference, too. All four species of puffins live in the Northern Hemisphere. The 18 species of penguins live in the Southern Hemisphere.