Stefan Christmann / Emperor Penguin (Aptenodytes forsteri) colony huddling for warmth, Queen Maud Land, Antarctica

Anup Shah / Burchell's Zebra (Equus burchellii) and Blue Wildebeest (Connochaetes taurinus) herd crossing river, Mara River, Masai Mara, Kenya

Mitsuaki Iwago / Blue Wildebeest (Connochaetes taurinus) and Burchell's Zebra (Equus burchellii) herd migrating, Serengeti

Gerry Ellis / Burchell's Zebra (Equus burchellii) and Blue Wildebeest (Connochaetes taurinus) crossing the Mara River, Masai Mara National Reserve, Kenya

Gerry Ellis / African Lion (Panthera leo) kill surrounded by tourists, Tanzania border, Kenya

Michael Quinton / Red Squirrel (Tamiasciurus hudsonicus) four young at entrance to their nest in a tree cavity, Alaska

Gerry Ellis / Greater Flamingo (Phoenicopterus ruber) nesting colony with mud nests, Inagua National Park, Bahamas

Tui De Roy / Adelie Penguin (Pygoscelis adeliae) group crowding on melting summer ice floe, Possession Island, Ross Sea, Antarctica

Tui De Roy / Adelie Penguin (Pygoscelis adeliae) group crowding on melting summer ice floe, Possession Island, Ross Sea, Antarctica

Michael Quinton / Cutthroat Trout (Oncorhynchus clarki) group in spring, Henry's Lake, Idaho

Tui De Roy / Adelie Penguin (Pygoscelis adeliae) group crowding on melting summer ice floe, Possession Island, Ross Sea, Antarctica

Mitsuaki Iwago / Blue Wildebeest (Connochaetes taurinus) herd with Burchell's Zebra (Equus burchellii) crossing river during migration, Serengeti