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 felt comfortable enough to 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.