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Bat season has begun in San Diego

Natalie Borchardt stands on the edge of the San Diego River in Mission Valley as she describes “bat walks” the San Diego River Park Foundation hosts every spring and summer. Warm weather and the insects that come with it have coaxed bats out of winter hibernation.

One cool thing about bats is: They navigate and hunt using echolocation, where their high-pitched squeak bounces off insects in their path.

“It’s like when you stand in a canyon and you say, 'echo!'” Borchardt says hollering. “And you hear it back? That’s exactly what the bat is doing. They are sending out a frequency, and depending on what they get back, they can tell how far away that bug is.”


San Diego bat walks are popular. One guide told me that some have as many as 90 people showing up. Borchardt said they’ve had to cap attendance. She chose this part of the river for a future walk due to a good supply of river bugs and condo buildings with red tile roofs on either side.

Bats squeeze between the tiles for cover. It’s part of their urban habitat.

Borchardt said bats have brought the River Park Foundation’s partnership with boy and girl scout troops.

“So one of the projects that we offer is for scouts to design and build their own bat boxes,” she said.

One of those scouts is 17-year-old Tai Cassel Ingen. He built six bat boxes to earn his eagle scout rank, and three of them are now installed near the San Diego River’s edge in Julian. He said the bat box gives them a safe, sustainable place to live in that area.


“They were in an abandoned mine, which caused a lot of problems for them and had the risk of collapsing and destroying their habitat,” Cassel said. “So building a bat box gives them a multi-shelved kind of structure where several of them can roost in the same habitat together.”

Bat boxes look like a very large bird house with entry slats below. When asked why Cassel became interested in bats, he explains it’s simply because they’re bats.

“They’re mammals that can fly! Oftentimes we get caught up in that fantasy of flying. It seems mystical to have that kind of superpower,” he said.

“And beyond Batman there are a lot of witchcraft elements that are involved with them. And you have characters like Dracula; ... vampires can also turn into bats and shape-shift.”

Tai Cassel Ingen is shown with bat boxes he built to get his Eagle Scout rank. Undated photo
Susie Cassel
Undated photo of Tai Cassel Ingen is shown with bat boxes he built to get his Eagle Scout rank.

Yes, in our popular imagination, bats are gothic and mysterious. We rarely see bats; we glimpse them in the dark. Before she created bat programs, Natalie Borchardt said she used to be terrified of bats.

“I still get a little nervous when they divebomb my head!” she said. “I have heard that’s because I have light-colored hair, the insects reflect well off the hair, and so the bats come very close to you.”

Bat myth busters

“There are a lot of myths about bats. Do they attack you? Well, they don’t. Will they get in your hair? Nope. Do they drink your blood? Well … there are three species of vampire bats. None north of central Mexico, so none here, and only one of them goes for mammals,” said Don Endicott, a retired engineer, self-taught bat expert and a guide at many local bat walks.

He said San Diego has an incredible biodiversity among its bats. About half of the 45 bat species in North America can be found in San Diego County. The greatest threat to bats, he says, is a deadly disease called white-nose syndrome that’s spreading east to west in North America. That and the heavy use of pesticides that kill a bat’s insect prey.

The only actual danger bats present is the risk of rabies. Like skunks and raccoons, they can be vectors for the disease.

“County health requirement is if there’s human contact with a bat, it has to be tested for rabies,” Endicott said. “The bat has to be euthanized, and it requires sampling brain tissues.”

Never touch a bat. Even if it’s not rabid, it must be captured and killed. Endicott said if it’s still or struggling on the ground, better to trap it in a shoe box and call Project Wildlife.


  • San Diego is home to both the smallest and the biggest bat in North America. The smallest is the Canyon Bat and the largest, the Mastiff Bat, has a 22-inch wingspan.
  • There are 22 species of bats in San Diego County while there are 45 species in all of North America.
  • The most common bat in San Diego County is the Mexican Free-Tailed Bat, which is the fastest flier in the world. It can fly 100 miles an hour without diving.
  • Bats are the only mammals that fly, and their 1,330 species mean they account for 20% of mammal species.
  • Bats are not rodents. They are members of the chiroptera family and they bear a closer relation to primates than they do to mice.

Observing bats requires some technology that locates bats using echolocation. When a bat is spotted, it triggers a recording device that can capture a bat’s call at a frequency people can hear. A bat’s call is usually much too high for that.

Endicott says photographing bats typically requires a camera trap that can catch a bat flying above the water.

Bats are nature’s insecticide, helping to make San Diego reasonably bug-free. Endicott said they are pollinators of native plants such as agave.

And though they are fast and elusive, Endicott recalls one instance when a bat surprised him while camping in Joshua Tree National Park while riding his bike at twilight.

“And on the way back — it’s after dark — and I have my headlamp on. It’s a weekday, so nobody is on the road. And I look to my left, and a bat is flying — like my wingman, right off my shoulder, following me down the road because I’m bringing up insects to the light.”

If you’re interested in attending a bat walk in San Diego, go to the San Diego River Park Foundation website for more information.