Living with Bats

Article by Betsy C. Bolster, DFG Staff Environmental Scientist, originally published at "California bats: Myths and Realities" in Outdoor California Magazine's Sep/Oct 1997 issue.

Bats are flying rodents — bats are blind — bats fly into your hair and attack you — most bats are rabid . . . All are unfortunate misconceptions and myths! Bats are not rodents: They can see just fine, and they don’t fly into your hair when trapped in a room with you unless you are having a "big hair day" and they are frightened by your screaming and arm-waving!

Although you may never have a bat in your house, you cannot avoid them — they occur everywhere on our planet except the North Pole and Antarctica. Almost one-quarter of the world’s 4,400 species of mammals are bats. Twenty-four of the more than 900 species occur in California. IN California, bats occur at elevations ranging from below sea level to almost 11,000 feet. Our smallest bat is the western pipstrelle (Pipistrellus hesplerus), with an average wingspread of 7.5 to 8.5 inches, and an average body length of 1.5 to two inches. Contrast that with measurements of our largest species, the western mastiff bat (Eumops perotis) which has a wingspan of more than 21 inches and average body length of four to five inches.

As for the myth about rabies, less than on-half of one percent of bats carry rabies, and normally bite only in self-defense. They pose little threat to the people who do not handle them. Worldwide, 99 percent of the human deaths due to rabies each year are due to contact with rabid dogs, the primary vector of human rabies. The simplest way to prevent exposure to rabies is to avoid contact with any unfamiliar animal, and never handle wild mammals. Unlike "Cujo", Stephen King’s fictional rabid dog that terrorizes its family, rabies in bats takes a paralytic form, meaning the animal becomes subdued and may be found quietly resting on the ground. Never pick up a bat on the ground — instead, with gloved hands, use a piece of cardboard or newspaper in combination with a box or coffee can to pick up the bat and isolate it from people. Then call your county health department or animal control office to request they come pick up the bat.

For any bat trapped in your house and flying around, avoid flailing your arms and screaming. Instead, simply close interior doors, then open the windows and outside doors to let it escape. If necessary, wear leather work gloves and capture the bat in a container to relocate it outside.

Bats, like other mammals, have hair, nurse their young, and produce body heat internally. Unlike all other mammals, bats fly, using wings formed by a flexible, leathery skin membrane stretched between highly modified elongated fingers and forearms, leg bones and the tall. But unlike most small mammals, bats are long-lived (up to 30 years or more for some species), and most species produce only one young per year.

Scientists named the bat order Chiroptera, which means hand-wing in Latin. Chiropterans are divided into two suborders, the Megachiropterans (Old World fruit bats) and Microchiropterans (distributed worldwide, primarily insect eaters). The Megachiroptera suborder consists of one family with about 150 species of bats that inhabit the tropics and subtropics from mainland Africa east to Australia and the Pacific islands. This suborder includes the "flying foxes" which are bats with head-body lengths of 16 inches and wingspans of nearly six feet. Most Megachiropterans eat fruit, although some eat insects and nectar. Only a few members of this group echolocate (use ultrasonic sounds that humans cannot hear) to navigate, avoid obstacles and capture food in the dark. Most locate food and orient themselves using well-developed eyes and a strong sense of smell.

The second suborder called Microchiroptera contains the remaining 17 families (approximately 750 species) of bats. Microchiropterans have small eyes and echolocate. These bats have a wide variety of food specializations, including insects, flesh (fish, frogs, birds, other mammals), fruit, nectar, flowers, pollen, and blood. Only three species are vampire bats, and they occur only in South and Central America, and rarely feed on human blood. All of California's bat species are insect eaters except the Mexican long-tongued bat (Choeronycteris mexicana), which occurs in the extreme southwestern part of California and feeds primarily on the nectar, pollen, and fruit of desert plants.

Bats are shy, intelligent animals that are important to our ecosystem and of considerable benefit to humans.

Although uncommon in California, nectar-feeding bats are important to desert ecosystems because of their role as primary pollinators of giant cacti, including the renowned organ pipe and saguaro of Arizona. If seeing bats as beneficial is still difficult, think about drinking margaritas or other beverages containing tequila. The seed production of agave plants, from which tequila is made, drops to 1/3,000th of normal without bat pollinators. Bats do not benefit tequila drinkers alone. Important agricultural and commercial plants like bananas, balsawood, breadfruit, chicle (for chewing gum), cashews, dates, figs, mangoes, and vanilla also rely on bats for pollination and seed dispersal. Tropical bats are also key elements in rain forest ecosystems where they pollinate flowers and disperse seeds for numerous trees and shrubs. In California, research is underway through the University of California at Berkeley to examine the nutrient role bats may play in distributing important nutrients throughout forest ecosystems during their nightly travels to feed on and "recycle" insects.

Another benefit that bats provide is all natural pest control. Worldwide, bats are the most important natural predators of night-f lying insects. just one of California's little brown bats (Myotis lucifugus) can catch and eat 600 mosquitoes per hour. The 20 million Mexican free-tailed bats (Tadarida brasiliensis) from Bracken Cave in Texas eat 250 tons of insects nightly. A colony of ISO big brown bats (Eptesicus fuscus) can protect local farmers from up to 18 million or more crop-damaging rootworms each summer. Recognizing that bats help control insects and reduce the need for and expense of chemical pesticides, many farmers and vintners are now constructing bat houses or otherwise encouraging bats to reside on their property. Homeowners also construct or purchase bat houses to attract bats for pest control. Bat houses are often installed nearby a home or business to provide new lodging for bats evicted as unwelcome guests in the attic.

Why would bats want to live in a hot, stuffy attic? Or hang out under the eaves of a house, or even under a structure overhanging your front door? For some species, the crevice or cavity that a house provides is similar to the leaf, bark, cavity, or cliffface that they naturally roost in or under. Only four of our 24 bat species regularly tolerate human presence and are commonly found in buildings: the Mexican free-tailed bat, the Yuma myotis (Myotis yumanensis), the little brown bat, and the big brown bat. Six additional species are occasionally found in buildings: the western mastiff bat (Eumops perotis), the pallid bat (Antrozouspallidus), Townsend's bigeared bat (Corynorhinus townsendii), the long-eared myotis (Myotis evotis), the fringed myotis (Myotis thysanodes), and the long-legged myotis (,Wyotis volans).

Similarity to natural roosts is not the only attractive feature of a home. You and your neighbors probablv provide bug-attracting lights, ponds, or open areas for bats to forage over and around. All that flying about catching bugs requires lots of energy (more than 1,000 heart beats per minute!), so bats spend most of the rest of their time resting. Bats can lower their body temperature and metabolic activity in response to varying levels of activity, a process called torpor. Torpor ranges from shallow to deep, and may last for a few hours or several months. Deep, long-term torpor in winter is termed hibernation, during which the heart rate of hibernating bats may drop to 10 beats per minute. Periods of torpor are spent in a roost, usually a place protected from the dangers of temperatuf e extremes and predators. Some bats roost alone (solitary), and some roost colonially in groups ranging from 10 to 3,000. Those bats in your attic or under your roof tile or shake are usually colonial species that are probably dayroosting. They have found a warm, protected place to rest during the day. They are safe from predators, and have to use very little energy to stay warm and rouse themselves for nightly feeding. They may even be using your attic for a maternity roost. The extra warmth and protection it provides are ideal for raising youngsters. The bat hanging above your front door is probably night-roosting-residing there for a few hours each night to rest and digest food between feeding forays to nearby fields or cleared areas by homes.

Although bats hanging about your home or business provide free insect control and excellent fertilizer (guano) for your garden, some people are understandably reluctant to maintain large colonies of bats due to the urine staining bats produce and disconcerting noises they make when active (bats in an attic or wall are frequently mistaken for rodents).

Under current California law, property owners or their employees may legally remove bats from property when bats are damaging it. (It is illegal to capture or possess bats for any other reason without a permit from the Department of Fish and Game.) Beware of unscrupulous pest control companies, however, that want to poison or fumigate bats to kill them. Not only is the use of poisons or fumigants on bats illegal under both state and federal law, it's costly and doesn't solve the problem. Unless bats are removed and their access points sealed, more bats will be back next year. The best way to remove bats is by permanently excluding their access. A variety of humane exclusion techniques are available that let bats escape from, but not reenter, the roost in your building. Exclusion techniques should not be used during the maternity season if young are present, usually from about the beginning of April through the end of August, when young bats are unable to f ly and manage on their own. Besides being unnecessarily cruel, excluding bats during the maternity season can actually make the problem worse with the smell of dead baby bats and bugs they attract.

Despite the valuable role bats play in our ecosystem, losses are occurring at alarming rates worldwide. In California, 10 of our 24 bat species are currently classified as "Species of Special Concern," meaning that they have low or declining numbers of individuals, or low, scattered or highly localized populations that require active management to prevent them from becoming threatened or endangered species.

There are a number of people-related causes for the decline in California's bat populations. California's explosive population growth has decreased the amount of available bat habitat. Disturbance, closure, and pest control at colony sites (caves, mines, buildings, and bridges) have had serious adverse effects on bat populations. Colonial roosting bats are especially susceptible to human disturbance and subsequent mortality. Townsend's big-eared bats typically roost in caves or mines, and are so disturbance-sensitive that they have been observed to flee the roost when humans intrude, never to return. Their young, not yet able to fly, were discovered mummified, still hanging in the maternity roost where their mothers left them. Irresponsible or poorly managed recreational caving (spelunking) and cave tourism can also disturb roosting bats during the critical hibernation or maternity season. "Party" caves and mines, frequently strewn with beer cans, shotgun shell casings, fireworks, or other litter, are often the site of vandalism to vulnerable colonies of roosting bats. Evidence of cruel vandalism in the form of hair spray cans, matches, and incinerated bats is not uncommon in easily accessible caves and mines.

Bats use abandoned mine workings because mines are analogous to caves, with their openings and underground passages that can provide temperatures and humidity levels appropriate for roosting bats, as well as dens for other wildlife like bobcats, owls, snakes, and tortoises. Many abandoned mines have been summarily sealed off for hazard abatement, often resulting in the entombment of large colonies of bats. It is frequently possible, though, to fence off mine areas or install gates on mine openings that are safety hazards. The gates prevent human access, but still allow bats and other wildlife to pass in and out of the opening. Besides human disturbance, another threat to mineroosting bats is renewed mining in historic mine workings. The combination of the high price of gold, powerful digging equipment, and the use of cyanide to extract very small deposits of gold has made the mining of formerly unprofitable concentrations of gold worthwhile. The process destroys the old underground workings, creating an open pit. Although not required by law, some mining companies work with bat biologists to try and minimize the impacts of their mining operation on resident bats.

Other reasons for declines include logging practices that target old or dead trees (which are most likely to contain suitable cavities that serve as roosts for forest bats), removal of riparian (riverbank or stream side) forests (important to both solitary and colonial tree-roosting bats), and the extensive use of insecticides for agricultural, silvicultural, and mosquito abatement purposes. To learn more about the status of California's bat species and what can be done about their decling population, some state and federal agencies have begun studying bats in recent years. The Department of Fish and Game (DFG) has sponsored a number of its own studies (funded by the Income Tax Check-off Program) of declining bat species. The DFG funded two studies during the summer of 1997, both emphasizing Species of Special Concern. One study examined more closely the habitat requirements of forest bats in relation to logging practices; the other investigated which bat species occur on many of the DFG's lands in Southern California. Results of the studies should be available in 1998.

So, next time you're out at dusk, whether taking a neighborhood walk and seeing bats catching bugs under streetlights, or sitting by the campfire watching your silent, winged pest controllers at work, try and imagine what your world would be like without these gentle, beneficial creatures.

For more information on bats, building bat houses or to join the effort in conserving bat populations contact:
Bat Conservation International
P.O. Box 162603
Austin, TX 78716