Gentoo penguins near Danco Island, Antarctica

Penguins can't fly!

Unlike most other birds, penguins can't fly, though this one sure looks like it's trying—or jumping for joy since today is Penguin Awareness Day. Actually, these gentoo penguins on Danco Island, just off the Antarctic Peninsula, were photographed leaping out of the water as they return to their nests for breeding season, which starts in November.

Just as other birds are aerodynamically shaped, penguin bodies are aquadynamic, able to glide through water thanks to their streamlined shape and flipper-like wings. Gentoos are the fastest penguins, and can swim up to 35 kmph. While most birds have hollow bones to help them stay aloft, penguin bones grow solid as they mature into adults. The added weight of the dense bones helps the birds stay submerged as they dive into the cold Antarctic waters in search of tasty seafood.