A large number of mammals we encounter are diurnal, which means active and awake during the day and asleep at night. However, an entirely new set of mammals come alive when the sun goes down. These nocturnal mammals include many cats like bobcats and ocelots, small scavengers such as raccoons and all 18 species of tarsiers, a type of primate found on the islands of southeast Asia.
All About Mammals
Mammals are warm-blooded, vertebrate animals with hair. Their warm-blooded nature and fur allows them to maintain a higher constant body temperature even as outside temperatures change; this is extremely important for nocturnal mammals who brave the lower nighttime temperatures. A mammal’s hair also helps insulate its body while providing camouflage -- many nocturnal mammals have dark or patterned hair to better blend in with the shroud of darkness.
Nocturnal animals patrol the night. It may seem like a strange way to live, but nocturnality has several advantages. The majority of mammals sleep the night away, affording nocturnal animals less competition for basic needs such as food, water, shelter and space. Bats, the high-flying nocturnal mammals, take to the skies at night when competition for resources from diurnal birds is much lower. The cover of darkness also protects nocturnal mammals from predators; however, many predators (like big cats) are also nocturnal and ready to hunt in the dark.
The nocturnal mammal’s eye has adapted to the dark. What diurnal mammals see as pitch-black darkness, nocturnal mammals see as dim light or shades of gray. Nocturnal mammals have proportionally larger eyes than mammals who are awake during the day; a tarsier’s eye is so large it can’t even move in its socket. Their pupils are also able to open more widely in low light than the diurnal mammal’s pupils. Perhaps the most unique characteristic of the nocturnal eye is the tapetum, a mirror-like membrane that reflects light back through the retina for a second time, giving even the dimmest light another chance to register.
Certain nocturnal mammals, like bats, lack acute eyesight. These vision-challenged nocturnal mammals have extrasensory adaptations that allow them to thrive. Bats use echolocation to navigate through the darkness and find food, emitting high-pitched sounds that produce an echo as they bounce off objects. A bat can use that echo as a marker of distance between itself and the object, whether it be a tree to avoid or one of its favorite foods -- insects and fruit.
- National Geographic: Bobcat
- National Geographic: Ocelot
- Animal Planet: Raccoon
- Endangered Species International: Tarsier
- Colorado Parks and Wildlife: What is a Mammal?
- Woodland Park Zoo: Nocturnal Animals at Woodland Park Zoo
- PBS: The Nocturnal Eye
- World Wildlife Foundation: Tarsier: Peculiar Primate with Enormous Eyes
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Christina Stephens is a writer from Portland, Ore. whose main areas of focus are pets and animals, travel and literature. A veterinary assistant, she taught English in South Korea and holds a BA in English with cum laude honors from Portland State University.