BATS IN CORVALLIS, OREGON
(Ken Olsen's soundfile from Corvallis, Oregon will load, please be patient. A simple bat detector which will capture such sounds is shown at right.)
Bats are the only flying mammals, they use sound to locate their prey, and they live a very long time for such small animals. Oregon does not have spectacular congregations of thousands of bats like those found in Texas caves. The species found here are varied and interesting, but either solitary or found in small colonies.
While bats in other parts of the world feed on fruit, fish, nectar, or even blood, all Oregon bats dine on insects. They consume pests such as spruce budworm moths, tussock moths, mosquitoes, pine bark beetle moths and gypsy moths. A bat can catch up to 600 insects in an hour.
People who mean no harm to bats often do not
understand how vulnerable bats are to disturbance of their roosting sites. Thus
these beneficial and harmless animals have been killed or have been unable to
reproduce enough to maintain their numbers. While accurate counts of these
small, nocturnal, and widely distributed animals are very difficult, there is
evidence that some species are declining.
Bats are members of the order Chiroptera, meaning "hand-wing." Like all mammals, bats have warm blood and hair. They bear live young and nurse them with milk. Their wings are supported by long finger bones covered with two thin layers of skin, like webbing between your thumb and first finger. This skin covering extends to the legs and, in some species, between the legs to the tail. Bats can use the wing and tail membranes to scoop insects. Bats have small, movable thumbs on the top of their wings for grasping and climbing. Their back feet are used for hanging.
Wings make bats look bigger than they really are. The biggest bat in Oregon is the Hoary bat, which weighs about an ounce, or about the same as five quarters.
Bats are competent fliers, although generally not as fast as birds. While they can fly 20 to 30 miles per hour, their average hunting speed is about 10 miles per hour. Bats can maneuver better than most birds - they can hover over one spot and can dodge obstacles easily. They actually chase insects in the air, not just bump into them.
Bats can see, but insect eating bats rely on echolocation to capture their food in darkness. Bats emit high-pitched (ultrasonic) sounds through their mouth or nose (depending on species) and listen for the returning echo. This is a fast, efficient and very detailed source of information for them. Some moths emit their own blips to scramble the bat's sonar. People usually can't hear bat vocalizations, even if they are very "loud," because they are pitched above our range of hearing. Many bats have big ears and elaborate flaps and folds around their nostrils to enhance echolocation, making their faces look odd. Echolocation is very different from our ways of perceiving the world, but bats have perfected it and can easily catch a tiny gnat on a dark night while dodging through branches. Bats sleep during the day and rest during the night in roosts. Day roosts are often crevices or cavities in rocky cliffs or trees, especially large snags. Night roosts are more exposed than day roosts and may be trees or buildings, bridges, carports or eves.
Mother bats congregate in small maternity colonies. Female bats will return year after year to the same safe, warm nursery roost. The males do not participate in raising the young and usually roost elsewhere. Baby bats are born in June or July. A female bat usually has just one baby at a time, although twins are normal in some species.
The babies are born hairless, but they have curved claws for clinging to their mothers. The mother can fly with the baby attached, but usually she leaves her young hanging at the roost site while she feeds. The babies are able to fly in three to five weeks.
In late summer and early fall, bats build up fat reserves for hibernation or migration. They also breed in the fall, although the babies are not born until the following summer. Most of Oregon's bats hibernate during the winter in caves, abandoned mines, buildings and hollow trees. Hoary, silver-haired and Mexican free-tailed bats migrate south for the winter. When it's time to hibernate, a bat hangs in a roost site that combines safety with the right temperature and humidity. Its body temperature drops to the level of its surroundings and its metabolic rate slows considerably. The bat may spend several weeks or months in this torpid condition, living on stored fat.
Bats have few natural enemies (owls
are one) and may live as long as 30 years. They are naturally abundant mammals,
although we rarely see them. One or two babies per year per female is normally
enough to maintain the population. However, if humans damage their habitat, it
may take several years for the population to recover because of the low rate of
reproduction. Bats are very susceptible to human activities, especially any
disturbance of roost sites. Other activities such as logging, spraying
pesticides and draining wetlands also affect bat populations.
Bats are easy to distinguish from other mammals simply because they have wings. In the field, their twisting flight pattern and nocturnal activity separate them from birds, although many people confuse bats with swifts. About 1,000 species are found throughout the world, 15 of them in Oregon.
Big brown bat (Eptesicus fuscus).
This is a relatively large bat, with a wingspan of 13 to 14 inches. The large size dark color and slow flight help identify it. It is more likely to be active in cold weather than other bats. Ears are relatively short and black. It is common throughout the state and prefers human structures for roosting, so this bat is seen fairly often. It usually lives in colonies, often with other kinds of bats.
Myotis bat (Myotis spp.).
Seven species of the genus Myotis liven in Oregon, all of them small brown bats with wingspans of 10 inches or less. Many are difficult to identify; most live in forests. The little brown bat is the most common and is frequently found in buildings. The fringed myotis and the western small-footed myotis are the least common. Myotis bats dwell in rock crevices, trees and human structures. As a group, myotis bats are the most abundant in Oregon, but several species are declining and/or are species of interest by the U.S. Fish and Wildlife Service.
Hoary bat (Lasiurus cinereus).
This is one of the most colorful bats in Oregon. It is also the biggest bat in Oregon, with a wingspan of nearly 16 inches. The body has dark fur tipped with white. The face has a dark mask, with a yellow-orange throat. The nearly round ears are edged in black. It is distinguished from the similar silver-haired bat by these markings and by patches of stiff, light tan hairs on its wrists. This impressive solitary bat roosts among the branches of both deciduous and coniferous trees throughout the state and likes to feed around permanent outdoor lights. They do not roost in buildings. This fast-flying bat migrates to southern California or perhaps beyond, returning to Oregon in the spring. It often bears twins.
Silver-haired bat (Lasionycteris noctivagans).
This solitary bat found in old growth forests has a wingspan of about 10 inches. The fur is glossy black, tipped with white. This bat looks somewhat similar to the hoary bat, but it is found throughout Oregon. This is usually the first bat out in the evening, emerging about 30 minutes after sunset. It often forages over woodland ponds, streams, meadows and roads, often flying very low. Like the hoary bat, it usually bears twins. It often roosts behind loose tree bark.
Pallid bat (Antrozous pallidus).
This is a large, pale bat with huge
ears, large eyes and a dog-like face. Its wing beat is slower than most bats.
It emerges late at night to feed primarily on the ground, eating large beetles,
crickets and scorpions. It produces a musky odor when disturbed. The pallid
bat is uncommon and is found mostly in arid regions and canyons.
Townsend's big-eared bat (Plecotus townsendii).
This is a medium-sized bat with enormous inch-plus long ears. It is gray, brown, or black and has a large lump on each side of its nose. It is generally active only after full darkness and sometimes collects insects from the air, as well as on plants. This is the bat most often found in caves; it usually hibernates instead of migrating. This species is very vulnerable to human disturbance and its numbers are declining sharply across its entire range, which includes most of the western United States. In Oregon, it is classified as a sensitive species in the "critical" category.
Western pipistrelle (Pipistrellus hesperus).
The smallest bat in the United States, this species weighs less than one quarter ounce (5 grams). The fur is pale yellow or brownish gray. The ears are relatively short and it has a dark face mask. This bat is common only in the Owyhee uplands in extreme southeastern Oregon. It flies early in the evening, well before dusk, and has a characteristic fluttering light.
Spotted bat (Euderma maculatum).
Spotted bats are rare in Oregon and seen only on the east side of the state. This is a medium-large bat with ears longer than those of any other bat in the U.S. It has dark fur with three large white spots - two on the shoulders and one on the rump.
Brazillian (Mexican) Free-tailed bat (Tadarida
Roseburg, Oregon may be the most northern part of this bat's wide range. This is a fast-flying, medium-small bat with long narrow wings and a tail that extends beyond the membranes. This is the bat found in huge colonies in Texas. It appears to survive the cold winters in Oregon by staying in heated buildings instead of hibernating or migrating, often sharing these quarters with other bat species.
The Oregon Department of Fish and Wildlife is protecting old mines used by bats from human disturbance, advising people who have bats in their buildings, working with consultants on designing bridges so that bats can use them as roosts, and surveying the state's population of Townsend's big-eared bats. Many of these activities are in cooperation with the U.S. Forest Service, Bureau of Land Management, Bat Conservation International, The Forest Industry, U.S. Fish and Wildlife Service, Oregon Department of Transportation, Oregon Department of Forestry, other agencies and private landowners.
Less than 1/10 of 1 percent of all bats are believed to carry rabies. Infected bats are rarely aggressive and soon die of the disease. Nonetheless, always avoid contact with any bat. If you are bitten or scratched by a bat, or any other wild animal, or have any contact with the animal's saliva, report it to your doctor and local health authority immediately. Capture the bat, if possible.
Here are some tips for peaceful co-existence with your bat neighbors.
from the State of Oregon