Nocturnal animals

At nightfall, many animals are just beginning to wake and to function. All of these night creatures are called nocturnal animals. Folklore often brands them as evil, inimical creatures. This is not so; they are merely different from diurnal animals, which are active during the day. Their activity during the hours of darkness is usually due to a combination of factors. First, the nocturnal animals may make use at night, without having undue competition, of food sources and habitats also used by diurnal animals. Second, they may be safe from many predators who would hunt them during the daylight hours. Finally, nocturnal animals may be predators which, at night, have much less competition for prey or have a better chance to capture it than in daylight.

Most nocturnal creatures are highly adapted to living under conditions with little or no light. These adaptations enable nocturnal animals to find their way through the world, locate food, and detect danger in almost total darkness. Although the diurnal species outnumber the nocturnal creatures, almost every type of creature living on Earth has a nocturnal version.

Regular Senses and Special Senses

Diurnal animals survive as long as they have a combination of senses that enables them to fit successfully into a daylight ecological niche. This usually includes the ability to see adequately, to hear well, and to have a useful sense of smell. The ability to see, hear, and smell falls within a fairly broad range among Earth’s many successful diurnal animals. Furthermore, weaknesses in one sense, such as the nearsightedness of the rhinoceros, may be compensated for by the enhancement of one or more of the other senses. In rhinos, both the ability to hear and smell are very well developed.

Nocturnal animals live under conditions that are skewed far away from the normal visual range of diurnal organisms. They must operate under conditions where there is either very little light or even no light at all. For this reason, all animals that are nocturnal have at least one sense, sight, hearing, smell, taste, or touch, that is very highly developed compared to those who are diurnal. These powerful sense adaptations enable them to survive well in the dark hours. The extent of such special sensory development varies, depending upon the organism, its needs, whether it also functions during the day, and the extent to which it is subject to predation by other organisms. Sometimes, senses not seen among diurnal animals operate in nocturnal animals.

The large, carnivorous felines, such as lions, tigers, or leopards, are not threatened by many other organisms. They survive well by using a combination of keen eyesight and hearing, as well as an excellent sense of smell. To further aid these big cats, their eyes face forward, allowing very accurate judgment of distances when they hunt. They also rely quite heavily upon very acute reflexes, great strength, and the ability to run down most prey hunted.

An extreme in visual development is seen in owls, which are the ultimate nocturnal avian raptors and which function and hunt almost exclusively at night. These birds are gifted with superb vision, fine hearing, and a very wide visual and aural range. For example, the night vision of many owl species is one hundred times more sensitive than that seen in humans. In addition, owl hearing is very acute, aided in some cases by possessing asymmetric skulls with the two ears at different places, further enhancing their hearing. Another adaptation that optimizes owl vision and hearing is the ability to turn the neck 270 degrees. This gives owls the widest aural and visual range of all birds. It is therefore, unsurprising that owls hear even the tiniest squeak or rustle made by their prey on the ground below them and then very efficiently locate the prey by vision.

Bats function only after the sun sets, most often feeding on insects captured while in flight. They have good hearing. However, their eyes are small, and they possess relatively poor vision. Perhaps this is why they have developed a special sense, sonarlike echolocation, to pinpoint insect prey in the dark night skies and to navigate. In bat echolocation, sounds (often clicks) are emitted from the larynx or nose of the bat, depending upon the species. These sounds then strike insects (and rocks or trees) and echoes bounce back to the bat’s ears. The bat then uses the echoes to find its prey. Many bats have developed means to direct the sounds they make for echolocation. For example, bats with skin flaps on the nose often use them to direct sounds in the nasal passages. The excellent hearing found in bats is aided by their large, mobile, external ears. Bats are not “blind as bats.” For example, they can use vision to navigate their way home and often do. Some nocturnal birds, such as the nightjar, also use echolocation to capture their prey.

Rattlesnakes and many other snakes locate their prey in total darkness in another way that involves special sense organs. This process is most sensitive in poisonous snakes called pit vipers. These snakes have two heat-sensitive pits located on the sides of their heads. The pits help them to detect small animals which are their prey, such as rodents or birds. The detection is possible because the prey sought are warmer than their surroundings. The pit viper heat sensors are large groups of nerve endings so sensitive that they can detect the body heat of a rodent over a foot away. The heat discrimination of the pit nerve endings is huge, and they can identify a temperature difference of less than one-hundredth of a degree.

Nocturnal Animal Habitats

People generally think of nocturnal animals as living in the wild. However, many live cheek-by-jowl with humans in parks, gardens, and empty lots in urban and suburban areas. Just a few examples are badgers, raccoons, deer, and foxes. People often see them and view them as pests or problems because they raid gardens and garbage cans, and some kill pets. Another problem associated with nocturnal animals is that they can carry severe, contagious diseases (for example, foxes and raccoons may carry rabies), which can be fatal to people. Finally, many nocturnal species are on the verge of extinction. These range from insects to the big cats. A few nocturnal species, such as tigers, are finally being covered by international conservation agreements, perhaps just in time. The others should be helped to survive, too.

Principal Terms

Auditory: pertaining to hearing

Diurnal: awake and functional during the daylight hours

Echolocation: sonarlike determination, from sound echoes, of the positions of unseen objects

Pinna (pl. pinnae): a term indicating the external ear of an animal

Pit Viper: a poisonous snake, such as a rattlesnake, which detects its prey via paired heat-sensing pits in its head

Tympanic Membrane: the eardrum

Bibliography

Boot, Kelvin. The Nocturnal Naturalist. North Pomfret, Vt.: David and Charles, 1985.

Brown, Vinson. Knowing the Outdoors in the Dark. Harrisburg, Pa.: Stackpole, 1972.

Kappel-Smith, Diana. Night Life: Nature from Dusk to Dawn. Boston: Little, Brown, 1990.

Lawlor, Elizabeth. Discover Nature at Sundown. Harrisburg, Pa.: Stackpole, 1995.

Marent, Thomas, and Thomas P. Peschak. “Nocturnal Animals Facts and Information.” National Geographic, 8 Jan. 2019, www.nationalgeographic.com/animals/article/nocturnal-animals-explained. Accessed 3 July 2023.

Pettit, Theodore S. Wildlife at Night. New York: G. P. Putnam’s Sons, 1976.

Popper, Arthur N., and Richard R. Fay, eds. Hearing by Bats. New York: Springer-Verlag, 1995.