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Bats have many positive benefits, unless they're living under your roof

  • Nanette Londeree
  • Bats. Their mere mention evokes visions of silent, blood-sucking creatures that haunt the night skies, or so the scary movies would have us believe. Centuries of superstition and misinformation have landed the furry, winged mammals with the undeserved reputation of nighttime villain.

    Well, it's not so. Overall, bats provide positive benefits to the environment, consuming huge numbers of insects, pollinating plants and dispersing seeds. As long as they're not roosting under your roof, it's a good thing to have them flitting about your garden.

    Belonging to the family Chiroptera, meaning "hand-wing," this incredibly diverse group of mammals has more than 1,100 species - about one-fifth of all mammal species. From the tiny bumblebee bat weighing less than a penny to giant flying foxes with 6-foot wingspans, these somewhat prehistoric-looking animals (bat fossils have been found dating back to the age of dinosaurs) are found around the globe in all but the harshest environments. Like all mammals, they have hair, bear their young live and nurse them. They are the only truly flying mammal with anatomical structures that allow for full-powered flight. For their size, they are the slowest reproducing mammals on earth (on average, mother bats rear only one pup per year), and are long-lived (five to 30 years depending on species).

    "Blind as a bat" is one of many misconceptions - all bats can see and many have excellent vision. Their dominant navigational method, like dolphins, is "echolocation." They travel and hunt at night by sending out beeps and analyzing the echoes that come bouncing back. With this finely-honed ability, they can detect obstacles as fine as a human hair in total darkness.

    More than two-thirds of bat species consume nocturnal insects such as moths, gnats, beetles and crickets with extraordinary appetites. A single little brown bat can eat up to 1,000 mosquito-sized insects in an hour. The bats in Bracken Cave in central Texas, home to the world's largest colony (some 20 million Mexican free-tailed bats) emerge at dusk like a river of wings and devour up to 200 tons of insects on a single summer's night. That's a lot of natural pest control!

    Most of the remaining species feed on the fruit or nectar of plants, playing vital roles as plant pollinators and seed dispersers. About 1 percent of bats eat fish, mice, frogs and other small invertebrates. And dreaded vampire bats? There are three species, all living in Latin America, which feed on the blood of cattle, horses and wild mammals. They don't suck blood Dracula-style; after finding a thin-skinned spot on the animal, they make a small incision and lap it up like kittens do milk.

    Insect-eating bats roost in tree foliage and cavities, under loose bark and in caves and crevices. As their natural habitats continue to disappear, more species are taking up residence in buildings and homes; the pallid bat (Antrozous pallidus), the big brown bat (Eptesicus fuscus), Mexican free-tailed bat (Tadarida brasiliensis) and Myotis species are the most common in our area. While you and your garden may benefit from a small colony of bats living in neighboring trees, having them living under your roof can cause problems. Squeaking and scratching sounds in attics, walls or chimneys especially during the warmer months at dawn and dusk are audible indicators of their presence, while visible signs include fecal droppings (guano) and urine that accumulate and stain ceilings and walls. Not only are these waste products undesirable, they can attract other insects and have a strong, unpleasant odor.

    Bats do have the potential for transmitting disease, particularly rabies. It's estimated that one in every 1,000 bats is infected with the disease, and exposure to humans is generally through handling infected animals. Generally, sick bats will be on the ground, so don't pick one up or handle it. For assistance, contact WildCare in San Rafael at 456-SAVE (7283) for guidance on what to do if you find injured or orphaned wild animals in your home or garden.

    If you find a bat stuck in your home, most likely it's an errant traveler, young and lost, rather than a sick one. First, don't panic; next, isolate the room the bat is in by closing off all openings; then open all doors and windows in the isolated room so the bat can find its way out. Once you've seen the bat exit, close everything. For more detailed information on removing bats from indoors, go to Bat Conservation International's website, www.batcon.org, for a video with step-by-step instructions.

    If you need to remove a colony of bats from your home, you'll first need to identify their entry points. Look for holes or cracks beneath eaves, around chimneys, air and plumbing vents and loose boards. (Don't attempt this May through September when parents are caring for their flightless young - most bats leave in late fall when you can introduce your exclusion methods.) Seal entryways with caulking, putty, duct tape, self-expanding polyurethane foam or hardware cloth (1/4-inch mesh) after you have excluded the bats. If you want help with removal or exclusion, contact WildCare.

    Some summer evening, take a seat in the garden right after sunset, and for the next hour, see if you can spot some of these shy little critters swooping about in search of a meal of mosquitoes. With a little information and understanding, you can protect a little piece of their habitat right in your own backyard, and reap the benefits.


    - UC IPM, www.ipm.ucdavis.edu

    - Bat Conservation International, Inc., www.batcon.org

    - Organization for Bat Conservation, www.batconservation.org

    - WildCare, www.wildcarebayarea.org