Central Oregon Bats


People often associate bats with caves. Some parts of the United States have thousands of bats inhabiting a cave, but there are only a couple hundred bats inhabiting caves in Central Oregon. Bats are extremely sensitive to human disturbances, and during times like hibernation or maternity, disturbances may lead to their death. Remember to clean your shoes before and after entering a cave to prevent the spread of white nose syndrome.

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Western Small-footed Myotis (Myotis ciliolabrum)

In Oregon, the species only occurs east of the Cascade Range. They are most common in arid and semi arid habitats, such as deserts and badlands, but may be found in pine or juniper forests, especially at higher elevations. They are nocturnal, feeding on moths, beetles, and flies. Their flight is slow but maneuverable, and they often feed close to water or to rocky bluffs. Their diet includes flies, beetles, and moths. They often roost during the day in caves, but may also be found in smaller crevices, artificial structures, or under loose bark. Males typically roost alone, but females may gather into small groups of up to nineteen individuals. They hibernate from November through February, typically alone. The Western small-footed myotis rears its young in cliff-face crevices, erosion cavities, and beneath rocks on the ground. Some females care for their pups alone, while others form small groups.

California Myotis (Myotis californicus)

The California myotis bat ranges throughout western North America from southern Alaska south into Guatemala and is one of the most abundant bats in semi-arid habitats, though it also can be found in ponderosa pine woodlands. Like many species, California myotis switch roosts on a regular basis. Throughout its range, it roosts beneath loose bark and in crevices of old snags, as well as in tree crevices. Early in summer, they form small maternity colonies in cliff crevices, buildings, and bridges. In winter, these bats roost in mines, caves, and buildings. Their diet consists of a variety of insects including midges, flies, and cranflies. They are active at night, although healthy bats will occasionally fly in the day. In 1950, a bat was seen flying through a Ponderosa Pine forest outside of Sisters, Oregon at 9:00 a.m. Others of this species have been seen through midday throughout the years.
Photo: Frank Carey

Long-eared Myotis (Myotis evotis)

It is primarily a bat of coniferous forests in much of Oregon but may occur far from trees in shrub-steppe regions of the state. It forages in openings in dense forest, between the trees beneath the canopy in ponderosa pine, and over willow-bordered creeks. Long-eared bats emerge from ten to forty minutes after full darkness and feed among the trees. Their diet includes moths, beetles, and flies. The Long-eared myotis often day-roosts in buildings but may use many other natural and man-made structures including caves and mines, bridges, hollow trees and loose bark on trees, and fissures in rock outcrops. Small maternity colonies form in late spring or early summer; maternity colonies of twelve to thirty females have been found in buildings and hollow trees.
Photo: A. King

Long-legged Myotis (Myotis volans)

Long-legged myotis are especially dependent on wooded habitats from Pinyon pine-juniper forests to coniferous forests. These bats are typically located in openings or along forest edges where they receive a large amount of daily sun. They are more commonly found at elevations of 4,000 to 9,000 feet, but they also live in some desert and riparian habitats. Long-legged myotis forage over ponds, streams, and in forest clearings, most often in search of moths.Radio-tracking studies have identified maternity roosts beneath bark and in other cavities. Though maternity colonies are most often formed in tree cavities or under loose bark, they also are found in rock crevices, cliffs, and buildings. One baby is born in the summer. This species hibernates in winter instead of migrating southward.

Hoary Bat (Lasiurus cinereus)

The largest bat in Oregon, hoary bats are found at scattered localities over most of the region west of the Cascade Range and in coniferous forest east of the Cascade Range. They are not desert specialists, but do frequent desert canyons. Hoary bats have been found in a variety of other roosts including squirrel nests, cavities in trees excavated by birds, and on the sides of buildings. They typically roost 10-15 feet up in trees along forest borders. In the summer, Hoary bats don’t emerge to feed until after dark. They sometimes make round trips of up to 24 miles on the first foraging flight of the night, and then make several shorter trips, returning to the day roost about an hour before sunrise. Their diet consists primarily of mosquitoes and moths. This bat roosts in branches of trees and likes to feed around outdoor lights. Hoary bats migrate south in winter. Traveling in waves, they are often found in the company of birds. Migration waves have been observed in spring and Autumn. Spring migration appears to begin in April in the southern US, and autumn migration begins in August in the northern regions of the United States and southern Canada. Those that live in the Pacific Northwest bats winter in California from San Francisco to the Mexico border.
Photo: Paul Cryan

Silver-haired Bat (Lasionycteris noctivagans)

Silver Haired Bat
The Silver-haired Bat lives statewide in Oregon, except for most of the Columbia Basin. They are most closely associated with coniferous or mixed coniferous and deciduous forest types, especially in areas of Old Growth. Silver-haired bats feed predominantly in disturbed areas, sometimes at tree-top level, but often in small clearings and along roadways or water courses. They emerge fifteen to forty five minutes prior to full darkness. Adults generally feed singly, but groups of three to four are occasionally seen. Though their diets vary widely, these bats feed chiefly on small, soft-bodied insects such as flies, midges, leafhoppers, moths, and mosquitoes. When they are feeding they tend to be very low to the ground and slow fliers.During migrations in May and September they inhabit rangelands where they forage along small streams. They form maternity colonies almost exclusively in tree cavities or small hollows. And like many forest-roosting bats, Silver-haired bats will switch roosts throughout the maternity season. This bat usually bears twins.

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Photo by Rachel Blomker

Canyon Bat (Parastrellus Hesperus)

They are the smallest bat in the United States. In eastern Oregon, they prefer rocky canyons and outcrops. It has been suggested that canyon bats use burrows made by rodents. They leave their roosting area in the early in the evening when it feeds on swarms of flying insects such as small flies and mosquitoes. It can sometimes be seen during the day along the lower Deschutes and John Day rivers sneaking out of its cliff crevice roost for a quick drink. Canyon bats do not seem to migrate far and may stay in the same area year round. They probably hibernate in mines and caves during winter. They start hibernation when the weather grows cold or food supplies diminish. However, both male and female members of this species will sometimes emerge during the winter months to hunt.
Photo: Bob Johnson

Spotted Bat (Euderma maculatum)

Spotted Bats are rare in North America. They are seen in dry climates where they use crevices in cliffs, caves, and canyon walls for day and night roosting. They also roost in trees adjacent to meadows at night. Spotted Bats are known to maintain exclusive foraging areas, traveling up to 25 miles to reach them, according to the Oregon State University NW Bat Hub. They forage in this area from about an hour after sunset till an hour before sunrise and are most active between midnight and three a.m. This species feeds solely on moths. They rip off the wings of the moth and eat only the abdomen portion. Spotted Bats can use their wings and tail membranes to catch insects.
Photo: Paul Cryan

Big Brown Bat (Eptesicus fuscus)

The Big Brown Bat lives throughout almost every American habitat ranging from timberline meadows to lowland deserts; they are more abundant in deciduous forest areas and suburban areas of mixed agricultural use. In eastern Oregon, it forages over the forest canopy, along roads through the trees, along the forest edge, over forest clearings, and along cliffs and canyon streams. These bats have formed maternity colonies beneath loose bark and in small cavities of pine trees and in buildings, barns, bridges, and even bat houses. Similarly to many bat species, reproductive females often can consume their body weight in insects each night. They eat a wide variety of night-flying insects including moths, mosquitoes, scarab beetles, and other beetles.
Photo: John MacGregor

Pallid Bat (Antrozous pallidus)

Pallid Bat
The Pallid Bat is uncommon and is found mostly in arid regions in canyons in southwestern and eastern Oregon. Pallid Bats are typically found in arid or semi-arid habitats, often in mountainous or rocky areas near water. They are also found over open, sparsely vegetated grasslands. During the day time, Pallid Bats typically roost in cracks and crevices, exfoliating bark of trees, or rocky outcrops. Roosts commonly are deserted and the bats move to alternate, frequently less-desirable roosts in response to the mere presence of humans in occupied caverns. During the night, this species will often use a night roost that is closer to their foraging grounds than their day roost. It emerges late at night to feed primarily on the ground, eating large beetles, crickets, and even scorpions. They forage on the ground, where it is adept at walking around in search of prey. Given an opportunity they are capable of consuming up to half their weight in insects every night. They form large maternity colonies in the desert canyon cliff walls. The Pallid bat is a pollinator of agave flowers. Its wing beat is slower than most bats.
Photo Credit: Pallid bat, Ann Froschauer/USFWS, Public Domain

Townsend’s Big-eared Bat (Corynorhinus townsendii)

The Townsend’s Big-eared Bat has been documented to live in all types of habitats. During summer, these bats inhabit rocky crevices, caves, and derelict buildings. In winter, they hibernate in a variety of locations including rocky crevices, caves, tunnels, and mineshafts, spaces under loose tree bark, hollow trees, and buildings. Males and females occupy separate roosting sites; males are typically solitary, while females form maternity colonies, where they raise their pups. A maternity colony may range in size from 12 bats to 200.
Males often hibernate in warmer places than females and are more easily aroused and active in winter than females. The bats are often interrupted from their sleep because they tend to wake up frequently and move around in the cave or move from one cave entirely to another.
Generally active only after full darkness, this species of bat almost exclusively feeds on moths and occasionally a variety of small insects. The Townsend’s Big-eared Bat is very vulnerable to human disturbance, and its numbers are declining.

Brazilian Free-tailed Bat (Tadarida brasiliensis)

Brazilian Free Tailed Bat
The Brazilian Free Tailed Bat is also known as the Mexican Free Tailed Bat. They occupy a wide variety of habitats, ranging from desert communities through pinyon-juniper woodland and pine-oak forests at elevations from sea level to 9,000 feet and higher. Brazilian Free-tailed Bats roost primarily in caves. However, they also roost in buildings of any type as long as they have access to openings and dark recesses in ceilings or walls. They are active from sunset to sunrise. They eat moths, beetles, dragonflies, flies, true bugs, wasps, and ants. It survives the cold winters in Oregon by staying in heated buildings instead of hibernating or migrating, often sharing these quarters with other bat species.

Mexican free-tailed bat, Ann Froschauer/USFWS, Public Domain, https://www.fws.gov/media/mexican-free-tailed-bat

Little Brown Bat (Myotis lucifugus)

Little Brown Bat Oregon
The Little brown bat lives throughout Oregon in a wide variety of habitats, but seems especially prone to establish residence near a lake, pond, or stream. The Little brown bat forages along the edges of vegetated habitat. These bats usually emerge about twenty to thirty minutes before full darkness and forage among scattered trees along edges of dense timber and along edges of water. They forage for 1.5 to 3 hours before stopping to roost. A second foraging bout usually occurs later in the night, ending at dawn. They eat wasps, moths, mosquitoes, and a variety of aquatic insects. Individuals can catch up to 1,200 insects in just one hour during peak feeding activity. They catch their prey with a membrane at the tail then transfer the meal to their mouth.During the day, these bats roost in tree cavities and crevices. In winter, this bat hibernates in caves. Around human habitation, they are often seen feeding in continuous circular patterns around buildings and small patches of trees, five to ten feet above ground. This species is especially associated with humans, often forming nursery colonies containing hundreds, sometimes thousands of individuals in buildings, attics, and other man-made structures.During the spring and summer, maternity colonies of almost all female individuals form. These colonies usually consist of several hundred bats. Outside of these maternity colonies, adult males and non-reproductive females will roost by themselves or in small aggregations. Maternity colonies begin to break apart in late summer. In midsummer, males and non-breeding females commence to congregate at a hibernating site, usually caves or abandoned mines. Females and their independent offspring follow shortly after. By August, populations are composed of both sexes.These bats will migrate hundreds of miles from their summer ranges to reach a suitable hibernating area that has high humidity. Little brown bats hibernate in colonies consisting of up to 183,500 individuals, though the average colony size is little more than 9,000.One baby is born in spring or summer. Young bats are capable of flight at about three weeks of age. They learn to fly in the home shelter, and they venture outside when about a month old.Little brown myotis bats are adept swimmers in the event that it falls into the water.

Photo Credit: Think Wild Central Oregon