Nocturnal, Diurnal, and Crepuscular Animals

When the nights grow longer and Halloween draws near, creatures like owls, coyotes, and bats seem to take center stage. Though we associate these critters with spooky scenes, these animals aren’t haunting the night, they’re simply living it! Have you ever wondered why certain animals are more visible at different times of the day or at night? Animals have developed unique adaptations to optimize survival during the day when they can maximize protection from predators, adjust to daytime/nighttime temperatures, and most easily locate their food sources. 

Animals that are active at night are described as nocturnal (e.g., owls, some rodents, raccoons, opossums, moths, some reptiles, and amphibians).  Those most active during the day are diurnal (e.g., eagles, hawks, bees, butterflies, squirrels, ducks, many reptiles), and animals that are most active during the twilight hours of dawn and dusk are described as being crepuscular (e.g., deer, rabbits, skunks, some bats).  However, it is important to note that animal patterns may vary as species will change their activity levels to adapt to environmental conditions, the prevalence of food sources, and the presence of human activity.

Nocturnal Animals

Nocturnal animals benefit from cooler temperatures, the absence of diurnal predators, and low light, where they use their keen senses to navigate at night to locate prey.  For instance, owls are raptors (or birds of prey) who possess exceptional hearing and vision, hooked bills, and sharp talons especially equipped for nighttime hunting. Their disproportionately large eyes have extreme rod-to-cone ratios (30 to 1) that support superior night vision.  Rods detect movement and light in low-light conditions, whereas cones require bright light for details and color.   Their eyes are in a fixed position situated in the front of the head, which provides binocular vision and excellent depth perception to gauge distance and movement.  To scan the entire visual field, owls must turn their heads 270 degrees in both directions.  Owls have excellent hearing, where asymmetrical ears triangulate sound waves to locate sound on a vertical axis and precisely pinpoint the location of prey (even if located under snow). Tufted feathers on their heads serve as camouflage, and their wing feathers allow for "silent flight" to surprise unsuspecting prey.

Diurnal Animals

Diurnal animals are most active during the daytime to avoid nocturnal predators. They respond to the rays of the sun and warmer temperatures and have strong eyesight which allows them to see well even in bright light. The ruby-throated hummingbird provides an excellent example.  Every spring, these tiny birds fly thousands of miles from Central America to Maine where they spend the warm summer months in the northern climate.  Given that they are acclimated to warm climates, the hummingbirds go into short hibernation (topor) during the cool Maine nights that lower their body temperature and slows their metabolism to conserve energy.  As the daylight approaches and the temperatures warm, they come out of their stupor and venture out into the day in search of nectar.  The ruby color of their throats (primarily in males) is a trick from sun rays hitting the feathers (which are black)  to create the prism of color that is visually attractive to females and intimidates potential rivals. These tough little birds will challenge any potential diurnal predator that threatens their babies, including larger birds such as eagles and hawks, snakes, and squirrels. 

Crepuscular Animals

Crepuscular animals are most active during the low-light periods of dawn and dusk as twilight hours tend to be cooler and not completely dark which helps them to avoid the primary hunting periods of both diurnal and nocturnal predators.  There is also less competition for food and other resources during these times. One of the best examples of a Maine crepuscular animal is the white-tailed deer.  Maine is home to the largest white-tailed deer population in North America and Mainers know to be especially watchful for deer while driving the roads during dawn and dusk.  White-tailed deer are highly equipped to detect and avoid predators while their extra-large and rotating ears provide exceptional hearing.  Their large eyes, situated on the sides of their heads, are optimized for seeing in low-light conditions and allow for excellent depth perception to see at long distances.  The deer also have a keen sense of smell which combined with their other senses puts them on high alert to locate and flee from potential predators.  Additionally, their fur changes color in the summer (reddish-brown) to fall/winter (gray) for maximizing camouflage to stay hidden from predators.

At Hirundo Wildlife Refuge, visitors have the chance to experience these nighttime rhythms firsthand. Our guided owl prowl events offer a unique opportunity to listen for owls, spot other nocturnal wildlife, and learn how these fascinating animals thrive after dark. You may even luck out and hear owl calls or spot bats at dusk on your own hike too!

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For more information:

About Owls. Owl Research Institute.

Brookshire, Bethany. (April, 2018). Scientists Say: Nocturnal and Diurnal. Science News   Explores.

Valerie (June, 2023).  Nocturnal, diurnal, and crepuscular animals: Differences explained plus examples. Wild Earth Lab.