Colorado is home to up to nineteen different bat species found across the state’s varied landscapes. These mammals are present in every environment, ranging from the eastern plains to high-elevation mountain forests and urban centers. They play an important role in controlling insect populations. Understanding these species and their habits helps residents coexist safely with these beneficial creatures.
Primary Species and Identification
The Big Brown Bat (Eptesicus fuscus) is the most commonly seen species in Colorado, often encountered because it prefers roosting near human development. This large bat has a wingspan typically measuring 325 to 350 millimeters. Its fur ranges from reddish-brown to dark chocolate. It is identified by its short, rounded ears and a broad snout, which contrast with the black coloring of its muzzle and wing membranes.
The Little Brown Myotis (Myotis lucifugus) is a smaller bat with glossy brown fur, weighing only about seven grams. Its wingspan usually falls between 220 and 270 millimeters. This species is widespread across North America, though its populations have declined in other regions.
The Pallid Bat (Antrozous pallidus) is a less common but distinctive resident, easily recognized by its very large ears, which can be almost half the length of its head and body. This large bat has a wingspan up to 410 millimeters and can weigh 30 grams. Its coloring is pale, ranging from creamy white to light yellowish-brown. It is unique among local bats for capturing its prey directly from the ground.
Habitat, Roosting, and Seasonal Activity
Colorado’s bats utilize a variety of habitats, including mountain caves, abandoned mines, rock crevices, and riparian woodlands. The need for shelter changes seasonally, requiring different types of roosts. Day roosts provide rest and protection, while maternity roosts, often found in attics or warm structures, are used by females to raise their single annual pup.
Bats also use cooler night roosts, such as sheltered porches or under bridges, for resting and digesting insect prey during foraging flights. As winter approaches, Colorado bats either migrate or enter hibernation. Hibernacula are typically caves, mines, or deep rock crevices where temperatures remain stable and cool, ideally just above freezing (around 35–40°F) to conserve energy.
The active season runs from spring through fall, when insects are abundant. When food resources become scarce, bats enter hibernation, a state of torpor that allows them to survive the winter without feeding. This seasonal pattern means human encounters are most frequent during warmer months when bats are actively foraging and establishing summer colonies.
Safe Interaction and Public Health Information
Bats are beneficial animals, providing a significant ecological service by consuming large quantities of insects, including agricultural pests and mosquitoes. For example, one Little Brown Myotis can eat over 150 insects in fifteen minutes, making them a natural form of pest control. Despite this ecological value, bats are the primary source of rabies exposure for humans and domestic animals, requiring caution during any interaction.
The rule for public safety is to never touch a bat with bare hands, even if it appears injured or dead. Rabies is a fatal viral infection. A bat bite can be so small that it goes unnoticed, especially if a bat is found in a room where a person or pet was sleeping. If physical contact is confirmed or suspected, the incident must be reported immediately to local public health authorities, and the bat should be safely contained for testing.
If a bat is discovered roosting in a structure, Colorado law mandates humane exclusion methods, as killing bats is illegal. Exclusion involves installing one-way devices over exit points, allowing bats to leave for foraging but preventing re-entry. Avoid exclusion during the maternity season (June through mid-August) to prevent trapping flightless young bats inside. After the bats have left, all openings larger than a thumb should be permanently sealed with mesh or caulk.