“In the end, our society will be defined not only by what we create, but by what we refuse to destroy.” –John C. Sawhill (1936-2000), president, The Nature Conservancy, 1990-2000
I walk to where the old wooden bridge used to be. I stop to watch the creek. It is barely moving. This being June, I did not expect it to be running, not in So Cal with no rain. I watch it anyway for any critter creekside activities, and I muse about the bats that live under the bridge. I wonder how they are doing.
Some years back (1998), there was a big County project to replace the wooden bridge with a cement one. The bridge was 70 years old and bats had lived peacefully there for decades. “But what about the bats?” cried one concerned citizen during a meeting about the proposed project. Thank goodness for my concerned neighbors, for the County was totally ignorant of the bats’ existence.
Officials put their heads together as to the bat issue. Their plan was to attach wooden “bat crevices” underneath the cement bridge, sort of critter condos. A bat census was taken with biologists taking the lead and volunteers selected to keep count of the bats. The volunteers were outfitted with “Tally Wackers” (a clicker for counting quickly with your thumb). The bat counters have to be very fast, as the bats come out at you all at once! Bats are very sensitive to noise and won’t fly if they think humans are watching them, so the census takers had to keep very still.
Besides taking the census, biologists also came back to study the Topanga bats with a device called an “anabat,” which records bat calls and is used to differentiate them. They recorded (9) different bat species. The (3) main ones were the Big Brown Bat (Eptesicus fuscus), the Little Brown Bat (Myotis lucifugus) and the Mexican free-tailed bat (Tadarida brasiliensis), with the latter being the most common under the bridge. They also discovered (2) environmentally sensitive species: the Pallid Bat (Antrozous pallidous) and the Western mastiff bat (Eumops perotis).
Everyone was abuzz with questions about bats. The Elementary School did their part to educate and satisfy the curiosity of all the Topanga kids. I guess all went well, though I am sure the bats would rather have the old wooden bridge back.
For my part, I learned that some bridges are used as roosts by male & juvenile bats, while other bridges contain roosts for nursing- maternity roosts, if you will. Besides bridges, bats could also roost in caves or tree hollows. The maternity period is from June to August. I don’t think our Topanga bridge was just a maternity roost, because many hundreds of bats lived there.
Bats are very helpful in the ecosystem. As they are the only mammal capable of sustained flight, they are important pollinators, seed dispersers and insectivores. They can eat over 600 insects each day! Perhaps the bats at the bridge are the reason we Topangans can sit by the creek on a summer’s night and not get bitten by mosquitoes!
Flying about catching bugs requires lots of energy (more than 1,000 heart beats per minute!) So bats need lots of rest. Bats can lower their body temperature and metabolic activity in a process called torpor. Torpor can last for a few hours or several months. Deep, long-term torpor in winter is called hibernation. Periods of torpor are spent in a roost, protected from extreme temperature and predators.
Bats can be found near homes with bug-attracting lights and ponds. If you have bats in your attic or under your roof, they are probably dayroosting, having found a warm, protected place to rest during the day while digesting a meal. They may even be using your attic for a maternity roost. Note: If you are trying to remove bats from your house, it is important to wait until Fall for the nursing period to be over.
In their role as pollinators, nectar-feeding bats are important to desert ecosystems of the Southwest because they pollinate cactus, such as the Giant Cacti of Arizona, and the Agave plants. Tequila lovers should thank the bats next time they sit down to a Margarita!
Bat population is diminishing worldwide. In California, 10 of our 24 bat species are currently classified as “Species of Special Concern,” meaning that they require active management to prevent them from becoming threatened or endangered species. California’s population growth has decreased the amount of available bat habitat. Disturbance and pesticides at bat colony sites (caves, mines, buildings, and bridges) have had serious adverse effects on bat populations.
As I stand down at the creek, I wonder if our bats have suffered any from noise & traffic since the new bridge was constructed. Just how are they doing in their new condos?
Do you have bats living nearby? We’d love to hear about them.
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
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