Rachael Long presented her talk “How Bats Protect California’s Billion-Dollar Walnut Crop” at the G Street Wunderbar at the Davis Science Café this past Wednesday, June 10th.
Long, a Farm Advisor for the University of California Cooperative Extension, said that California has 25 or 26 different bat species—the number varies depending on the year and conditions. Most of the bat species are migratory, moving south for the winters. A substantial colony of Mexican free-tailed bats spends its summers under the I-80 causeway in Yolo County.
“I think they’re following moths up the Central Valley,” Long said.
Studies show that bats in Northern California eat pest insects, Long said. Because of this, many people—farmers in particular—prefer to let the bats nest on their property. Even the G Street Wunderbar has bats: a portion of the wood paneling on the second floor warped, allowing a colony to move in. The owner of the bar proudly mentioned this fact during the evening, saying that the bats keep the mosquitoes away.
Long brought with her a commercially available bat house, just as she had when interviewed by Capital Public Radio on Tuesday. The houses—used by those who want to keep the bats around, but not in their barns or homes—are roughly a foot and half wide by two and a half feet tall, with a slot slightly smaller than an inch on the bottom. Over a hundred bats could fit in one of these, Long said, describing how the bats come in at a downward swoop, bank sharply for the slot, and flip upside-down in midair as they enter the slit and work their way inside.
This maneuver takes a couple of tries for the juveniles to master, Long said. They swoop in several times before actually managing to wedge their legs into the slot.
Long passed around a few bat specimens for the guests to see and touch. A Mexican free-tailed bat and a big brown bat were passed from table to table as guests marveled at their small size and soft fur. A light cream-colored pallid bat and a pepper-gray hoary bat also made the rounds.
Much to the audience’s surprise, Long also passed around a small container of bat guano, or feces. Long and her graduate student assistant Kate Ingram collect these samples in the field and send them to labs for genetic testing. They are looking specifically for codling moths, which lay their eggs in walnuts and can destroy a significant amount of the crop.
“Bats have very shiny poop,” Long said during her radio interview, and again at the science café. The shine is due to all the insect exoskeletons they ingest.
According to the preliminary data gathered by Ingram, some bats on walnut farms consume codling moths. About six percent of California’s walnut crop is protected by the flying mammals—roughly 3,000 bats are saving farmers about $30,000 worth of prevented crop losses.
Responding to an audience question on current threats to bats, Long answered that many bat colonies are losing their habitats and are being struck by large wind turbines, which the bats cannot see or hear in time to avoid. They are also susceptible to white-nose syndrome, a pale fungus that grows on the bat’s skin.
The event drew record attendance for the two-year-old cafe series. Event organizer Jared Shaw is considering the G Street Wunderbar as a permanent venue for the Davis Science Café, pending a public poll on the event’s Facebook page.
— James Eldred