Black-headed night monkeys in Pacaya-Samiria National Reserve, Peru

© Cyril Ruoso/Minden Pictures

Black-headed night monkeys in Pacaya-Samiria National Reserve, Peru

Since black-headed night monkeys are nocturnal, it’s surprising to see them awake during daylight hours. Perhaps here in Peru’s Pacaya-Samiria National Reserve, these tropical-forest dwellers felt comfortable enough to take a peek at the photographer while he worked. Night monkeys are the only nocturnal monkeys, and those large brown eyes gather enough light to let them see in the dark. Scientists have determined that night monkeys see in black and white. Color vision’s not necessary when you spend most of your waking hours in the dark.