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

© Cyril Ruoso/Minden Pictures

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

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