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Marin IJ Articles

Bats, a gardener’s true friend

  • Karen Gideon
  • Why do gardeners care about bats? We care because they are our most beneficial mammals. They are natural garden pest patrollers and nutrient cyclers as 70% of all bats are insectivores. Some bats are flower feeders, offering their pollinator services as they feast. One species loves agave and pollinates the plant that gives us tequila. Fruit-eating bats disperse seeds and help with reforestation.

    Right off the bat, let’s dispel some myths about these nocturnal creatures. Bats are not blind. They have good vision and use a type of sonar called echolocation to navigate. Out of 1,100 species of bats, only three bat species feed on the blood of cattle in Latin America. And while all bats do not have rabies, it’s possible to become infected by handling any rabid wild animal.

    Of all mammals on the planet, bats make up 20% of the total mammalian population. They’re the only mammals able to take true powered flight. That said, they are unable to launch to fly like a bird and must drop from a perch and swoop into flight. That’s why they roost hanging by their feet.

    Some species colonize and hang together, literally, engaging in extensive grooming. They have social structures and live in large colonies, roosting in caves, culverts, belfries and bat houses. Other species are more solitary, roosting in the bark of trees and man-made structures. Most females give birth to one baby a year and can live up to 40 years.

    Bats have been negatively effected by the loss of habitat, disturbance of roosting locations, climate change and the decline of insects due to overuse of pesticides. A disease called white-nose syndrome (WNS) is wiping out millions of bats across the country. The pathogen is a fungus that infects bats during the cooler months in hibernation, rousing them early so they use their stored fat prematurely and die of starvation in the spring. While WNS has recently been detected in Northern California, it has not yet been detected in Marin County.

    A consortium of agencies working together as the Marin County Bat Monitoring Project, onetam.org/our-work/bat-monitoring, is gathering information about Marin County bats. Led by the U.S. Geological Survey along with Point Reyes National Seashore, One Tam is studying where our 13 bat species roost, if and when they hibernate, where they hunt and what influences put them at risk. Using lightweight mist nets the scientists capture bats and fit them with radio tags for tracking.

    While bats are good for the environment and our gardens, it’s a bad idea to have them living in your home. Guano, or bat poop, is a powerful fertilizer, but it is also hazardous. It can attract parasites, mites and fleas and sometimes trigger an asthma attack due to airborne mold spores. If you have guano in your home, staining your siding or collecting in your attic, it’s time to contact a professional wildlife removal service.

    The most effective technique to eliminate bat visitors is exclusion, which is a system of narrowing tubes attached to the entrance and exit that allows bats to leave your home but not re-enter. Don’t exclude bats from May through September when they are tending their young. Repair and caulk any openings larger than ¼ inch to keep them out.

    If you find a downed or injured bat in your garden, call Wildcare (415-456-7283) for instructions on bat capture and transport. It’s important to emphasize that you should never handle a bat with your hands. Not only are you at risk for rabies but there are other pathogens that can be spread by wild animals that could make you sick.

    Bats are gardeners’ friends. Protect them by maintaining their natural habitats like tree hollows, snags and palm trees. Build a bat house in an isolated area in your garden with water nearby. You can promote a robust insect community by eliminating your use of pesticides.