Bats Bats are highly beneficial to people, and the advantages of having them around far outweigh any problems you might have with them. As predators of night-flying insects (including mosqui toes!), bats play a role in preserving the natural balance of your property or neighborhood. Although swallows and other bird species consume large numbers of flying insects, they generally feed only in daylight. When night falls, bats take over: a nursing female little brown bat (Myotis lucifugus) may consume her body weight in insects each night during the summer. Contrary to some widely held views, bats are not blind and do not become entangled in peoples’ hair. If a flying bat comes close to your head, it’s probably because it is hunting insects that have been attracted Figure 1. Big brown bat by your body heat. Less than one bat in 20,000 has rabies, and no (Photo by Ty Smedes) Washington bats feed on blood. More than 15 species of bats live in Washington, from the common little brown bat (Myotis lucifugus) to the rare Townsend’s big-eared bat (Corynorhinus townsendii). Head to tail, bats range in length from the 2.5-inch-long canyon bat (Parastrellus hesperus), to the 6-inch long hoary bat (Lasiurus cinereus). The hoary bat has a body approximately the size of a house sparrow and a wingspan of 17 inches. The species most often seen flying around human habitat include the little brown bat (Myotis lucifugus), Yuma myotis (Myotis yumanen sis), big brown bat (Eptesicus fuscus, Fig. 1), pallid bat (Antrozous pallidus), and California myotis (Myotis californicus). Facts about Washington’s Bats Food and Feeding Behavior • Washington bat species eat vast quantities of night-flying Bats are the only Figure 2. insects, including moths, beetles, mosquitoes, termites, true flying mammals and they and flies. belong to the mammalian order Chiroptera, which means • Most bats hunt in flight or hang from a perch and wait “hand-wing.” The bones in a for a passing insect to fly or walk within range. bat’s wing work like those of the human arm and hand, but The pallid bat captures crickets, grasshoppers, spiders, bat finger bones are greatly • elongated and connected by a scorpions, and other prey on trees or on the ground. double membrane of skin to • Bats locate flying insects primarily by using a radar system form the wing. known as “echolocation.” The bat emits high-pitched (Oregon Department of Fish and sound waves that bounce back to the bat when they strike Wildlife.) a flying insect. A bat locates prey by interpreting the reflected sounds. • Bats often capture insects when flying by scooping them into their tail or wing membranes, and then putting the insects into their mouth (Fig. 3). This results in the erratic flight most people are familiar with when they observe bats feeding in the evening. • Bats will fly 1/2 to 6 miles from their roost to a feeding site, using temporary roost sites there until returning to their main roost. Hibernation Sites • To cope with winter Figure 3. Bats often capture insects when flying by scooping them into their tail or conditions, most bats use a wing membranes, and then putting the insects into their mouth. hibernation site, called a (Oregon Department of Fish and Wildlife.) “hibernaculum.” (See “Bats in the Winter.”) • Hibernation sites include cavities in large trees, caves, mine shafts, tunnels, old wells, and attics. • The hibernaculum protects the bats from predators, light, noise, and other disturbances. Temperatures in the hiber naculum must be cool enough to allow bats to maintain a low body temperature but not freeze; humidity must be high and constant enough to prev ent bats from dehydrating. • Bats hibernate alone or in groups, and enter hibernation sites in late September or October. Nursery Sites • Most Washington bats breed during late fall or winter at their hibernation site. Females store sperm until the following spring, when fertilization takes place after the females rouse from hibernation. • The young, called “pups,” are born and raised in nursery colonies occupied only by breed ing females and their young. • Males roost alone or in small groups during this time, leaving the warm roosts and optimal feeding grounds to females. • Attics are often used as nursery sites because they maintain the warm temperatures, from 85 to 104 degrees F needed for raising young; the heat actually speeds the development of bat pups, both during fetal development and after birth. • Most bat species produce one pup in May, June, or July; the specific dates depend on the species, locality, and weather. • In the nursery, the young remain with their mothers and suckle frequently. • Pups are unable to fly for about a month, and are left in the nursery when the mother hunts. • Female bats may return to the exact location where they were born year after year. Mortality and Longevity • Bats have few predators. Hawks, owls, house cats, and raccoons occasionally prey upon them. • Heavy storms kill bats during migrations, and long winters can kill even more of them. • Through habitat alteration, commercial pesticide use, and control practices, humans are a main source of mortality among bats. Exposure to pesticides kills bats either directly through exposure, or indirectly through ingestion of sprayed insects. • For their size, bats are the world’s longest-lived mammals. The big brown bat has been recorded to live 19 years in the wild. The record for a little brown bat is 33 years. Viewing Washington’s Bats The safest way to view and enjoy bats is to watch them in action. Bats are fascinating flyers, zigging and zagging about as they chase and eat insects. Little brown bats and Yuma bats prefer to hunt over water. Big brown bats are often seen hunting along the margins of wooded areas, or silhouetted against the lighter sky as they twist and turn high above the tree canopy. It’s also fun to watch bats drink, which they usually do first thing after leaving their day roost. They scoop up mouthfuls of water with their lower jaws as they fly over lakes, streams, ponds, or water troughs. Most bats do not come out to eat or drink in heavy rain or when the air temperature remains below 50 degrees F. To view bats, follow these tips: Choose a warm summer evening and a place where you can sit and view the place where bats will emerge from a roost site or have been spotted in the air. When waiting for bats to emerge from a roost site, such as an attic or bat house, remain still and quiet, and listen for the squeaks or clicks that many species make before emerging. Some species of bats begin their night flights 20 to 30 minutes before dark—the common big brown bat may be out foraging earlier. The rare canyon bat from the arid regions of Washington emerges before the sun goes down, and has been seen foraging with violet-green swallows. Other species don’t emerge until after dark. The best places to see bats in flight are where night-flying insects abound, such as next to a stream, lake, or pond, over a meadow or large lawn, along a forest edge, or around bright streetlights or porch lights. With the aid of an inexpensive, commercial bat detector, listen for the echolocation calls bats make when navigating and locating prey. Bats in the Winter With few flying insects available to them during winter in Washington, bats survive by hibernating, migrating to regions where insects are available, or a combination of these strategies. During hibernation, metabolic activities are greatly reduced—a bat’s normal body temperature of around 100 degrees F is reduced to just one or two degrees higher than that of the hibernaculum, and their heart rate slows to only one beat every four or five seconds. A hibernating bat can thus survive on only a few grams of stored fat during the five- to six-month hibernation period. Banding studies indicate that little brown bats will migrate 120 miles between hibernacula and summer roosts, and, if undisturbed, they occupy the same site year after year. They select areas in the hibernaculum where there is high humidity (70–95 percent), and the temperature is 34 to 41 degrees F. Still, there are some species, such as the big brown bat, that can hibernate in relatively exposed situations in buildings where there is considerable fluctuation in temperature. Hibernation lasts until April or early May, but in coastal regions bats may arouse in late winter—little brown bats have been found feeding in the Puget Sound region in mid-March. It is important not to disturb hibernating bats. If a bat rouses early from hibernation, it must use its fat reserves to increase its body tempera ture. A single disturbance probably costs a bat as much energy as it would normally expend in two to three weeks hibernating. Thus, if disturbed multiple times, hibernating bats may starve to death before spring. It is important not to disturb roosting bats at any time of the year. In the spring, disturbing a maternity colony when flightless young are pres ent may cause young bats to be dropped to their deaths, or abandoned, by panicked females. Because some bats hibernate in buildings during the winter months, batproof a building only when you are sure no bats are hibernating in it. If bats are found hibernating inside after October 15, they should be left alone until early spring (prior to the birthing period in May) after the weather has warmed enough for insects to be out regularly.