Crepuscular creatures abound in our area.
Some are mammals. Others are birds. Some are insects. Others are fish, even reptiles.
With all this variety, what are the common traits that make them crepuscular? Crepuscular creatures are most active at dawn and dusk. They tend to sleep at night and lay low during mid-day. This differs from those animals that are nocturnal or diurnal.
The scientific studies
The word crepuscular is derived from the Latin word for twilight. There are subdivisions of crepuscular animals. Matutinal animals are active in the morning; vespertine animals, at dusk.
Scientists believe that some animals have evolved these patterns of activity as anti-predator adaptations. Twilight makes it challenging for nocturnal and diurnal predators to see. Some predators have adapted to being crepuscular as a means of better tracking their prey. Other creatures are crepuscular in order to avoid the heat of mid-day.
Nocturnal refers to animals that are most active at night and sleep during the day. Diurnal refers to animals that are most active during the day and sleep at night. Sleep patterns that are dictated by light and dark generate a circadian rhythm within animals that keeps them in time with a 24-hour cycle. Some creatures are defined as cathemeral or arrhythmic, meaning they are sporadically active at any time.
The animals have adapted to avoiding predation or enhancing hunting prowess. Climate can also dictate sleep patterns.
Crepuscular mammals
Cottontail rabbits, jackrabbits, mule deer, elk, moose, bison, ferrets, mice, rats, beavers and otters.
Crepuscular reptiles
Rattlesnakes and gila monsters
Crepuscular birds
Chimney swifts, hummingbirds, many songbirds,
Crepuscular bugs
Mosquitoes, moths and beetles.
Crepuscular fish
Brook trout
Nocturnal creatures
Foxes, nighthawks, skunks, bats, snowshoe hares, porcupine, badgers, milk snakes and most owls.
Raccoons are so nocturnal that, if seen during the day, they are potentially rabid. If you see one out in the daytime, stay away.
Diurnal creatures
Most raptors (hawks, eagles, falcons), bull snakes, pikas, butterflies and squirrels, and most lizards
Nocturnal, diurnal or crepuscular?
Some animals are tough to classify. While we tend to think of cats as nocturnal, they also see well during the day. Bobcats, cougars, lynx, and housecats, might be classified as cathemeral or arrhythmic. Others in this category include frogs, wolverines, coyotes, mountain goats and black bears.
MK Thompson is the assistant for conservation education, volunteer programs and visitor information services for the San Juan Mountains Association.
