Crepuscular creatures abound in Southwest Colorado.
They live in the high mountains, sage plains, ponderosa forests, desert canyons and everywhere in between.
They are all shapes and sizes.
Some are mammals. Others are birds. Some are insects. Others are fish. Even reptiles can be crepuscular.
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 midday. This differs from animals that are nocturnal or diurnal. Read on to learn why this is an efficient way for them to live and what local creatures live this way.
The word “crepuscular” is derived from the Latin word for “twilight.” There are subdivisions of crepuscular animals. Matutinal animals are most active in the morning while vespertine animals are most active at dusk.
Scientists believe that some animals have evolved these patterns of activity as anti-predator adaptations. The coarse light of twilight makes it challenging for both nocturnal and diurnal predators to see. In turn, 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 midday.
“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. These 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 during any time of day.
All of these sleep habits are behavioral adaptations. Animals have adapted to either avoiding predation or enhancing hunting prowess. Climate also can dictate sleep patterns.
Catching crepuscular creatures candidly
Crepuscular animals are found around the globe. The list is long, so let’s stick with creatures found in the Four Corners. Many of them are mistaken for nocturnal. Head out at dawn or dusk, and keep your eyes peeled for these animals.
Crepuscular mammals: cottontail rabbits, jackrabbits, ungulates (mule deer, elk, moose), bison, ferrets, mice and rats, beavers, river otters
Crepuscular reptiles: rattlesnakes, gila monsters
Crepuscular birds: chimney swifts, many song birds, hummingbirds
Crepuscular bugs: mosquitoes, many moths, many beetles
Crepuscular fish: brook trout.
Foxes, most owls, nighthawks, skunks, bats, snowshoe hares, porcupine, badgers, milk snakes, raccoons. Raccoons are so nocturnal that, if seen during the day, they are potentially rabid. If you see one out in the daytime, stay away from it and call the nearest state wildlife organization.
Most raptors (hawks, eagles, falcons), most lizards, bull snakes, squirrels (tassel-eared Aberts, chicory, ground), pikas, butterflies.
Nocturnal, diurnal or crepuscular?
Some animals are tough to classify. Take, for example, ermine. Some sources claim they are nocturnal in the summer but transition to diurnal in the winter. The same is said for bobcats. While we tend to think of cats as nocturnal, they also see well during the day.
Bobcats, as well as cougars, lynx and house cats, might best be classified as cathemeral or arrhythmic. Other animals in this broad category include frogs, wolverines, coyotes, mountain goats and black bears.
Also, the animals listed above are not necessarily confined to one category. Animals’ habits can vary depending on season and temperature. So if you still are uncertain about a particular animal’s sleeping habits, don’t lose sleep over it.
MK Thompson is assistant for education, volunteer programs and visitor information services for San Juan Mountains Association, a nonprofit dedicated to public land stewardship and education.