Playful Penguins Struggle To Keep Atop A Slippery Floating Chunk Of Ice

In this photo provided on Friday Feb. 15, 2013 by World Press Photo, the 1st prize Nature Stories by Paul Nicklen, Canada, for National Geographic magazine shows Emperor Penguins, even though they have evolved an incredibly advanced bubble physiology the greatest challenge they face is the loss of sea ice that supports their colonies and ecosystem. (AP Photo/Paul Nicklen, National Geographic magazine)