When Evan Cole set foot in the boarded-up basement of the abandoned pink house that sat atop a bluff overlooking Tunitas Creek Beach in Half Moon Bay, there was a grey-brown bat flitting around the ceiling above a wraparound white laminate bar.
“It was very cool to see it flying around inside this old ‘60s home on the coast,” said Cole, a natural resource manager with the San Mateo County Parks Department.
The bat in question was a Townsend’s big-eared bat, a species of special concern in the state of California. But it couldn’t stay in the old home. The structure, formerly owned by rock star Chris Isaak, was unstable and needed to be demolished as part of a county project to turn the area into a public park that’s slated to open next summer.
To mitigate the loss of the building as a bat habitat, the parks department built a small raised, enclosed structure for the bats to roost in nearby. It’s one of at least two recent county projects focused on getting to know the local bat species.
An abandoned home formerly owned by musician Chris Isaak was home to a Townsend’s big-eared bat, a species of special concern in the state of California. Courtesy San Mateo County Parks Department. 
A bat roost constructed by San Mateo County Parks Department at Tunitas Creek Beach. Courtesy San Mateo County Parks Department.
Beyond bats’ symbolism as creepy creatures at Halloween, San Mateo County is a year-round home to a number of different species regularly studied by wildlife experts to better understand their behaviors and help them coexist with humans.
“Bats utilize habitats in all different ways and at all different times and places,” Cole said. “And so it’s really important for us to be able to understand what bats we have present, so that we can do our best to avoid impacts to them.”
Bats, which are sometimes mistaken for rodents, aren’t the easiest creatures to study. They’re nocturnal, their migrations can cover very long distances and how they roost can be hard to fully understand, said Matt Sharp Chaney, a wildlife ecologist at Midpeninsula Regional Open Space District.
“Unless you just happen to be lucky, or you have the resources to pour into a really robust survey effort, there’s a lot you can miss,” Chaney said.
Pallid bats at La Honda Creek Open Space Preserve in San Mateo County. Courtesy Vishal Subramanyan/ Midpeninsula Regional Open Space District. 
A Townsend’s big-eared bat on Midpeninsula Regional Open Space District property. Courtesy Matt Sharp Chaney/ Midpeninsula Regional Open Space District. 
Mexican free-tailed bats at La Honda Creek Open Space Preserve in San Mateo County. Courtesy Vishal Subramanyan/ Midpeninsula Regional Open Space District.
For example, finding them in a forested environment is particularly tricky. Monitoring equipment may be set up on one side of a large tree to capture bats exiting a suspected roost. But if bats are pouring out from the other side of the tree, there may be no way of knowing, he said.
Chaney said 15 of the 25 species of bats found throughout California have been detected on MidPen property, which includes land in San Mateo, Santa Clara and Santa Cruz counties. Some local species include the Mexican free-tailed bat, the pallid bat and the hoary bat. Bats are also the only mammal on Earth that can fly.
In 2023, San Mateo County conducted a yearlong acoustic monitoring study in Pescadero Creek Park. A high-frequency microphone recorded bat calls for nights at a time. The mic was regularly moved to different locations where bats were likely to be foraging or flying, such as habitat edges where grasslands meet forests or through the creek corridor.
“And based off of the results of this effort, we do plan to continue monitoring different parks, different parts of parks and different seasons to try to really fill out that baseline inventory of what we have and where we have it and when we have it,” Cole said.
The recordings could inform the county about which species use the park and during which season.
Though bats are a hallmark of Halloween time, they appear throughout the county year-round. In the fall, bats start to migrate and look for a safe place to go into torpor to conserve energy if needed.
“(It’s) kind of like hibernating, where their heart rate slows and their breathing slows and they, basically, become inactive for a period of time,” Chaney said. “All of our bats in our area can do that.”
Chaney said that Western red bats may be found in piles of leaves in the autumn months. The tree dwellers go into torpor and fall out of their roosts when the leaves are dropping.
He added that members of the public should not touch bats if found on the ground, as some carry the rabies virus. Instead, a professional with animal control or wildlife services should be called to handle the mammal.
Bats also mate in the fall, but many females delay fertilization until the spring when there’s a boom of insects to snack on. From that point on and throughout the summer, female bats will establish maternity roosts to raise their pups together and males will find bachelor roosts.
A female will typically have one or two pups and “they put a lot of time and energy into raising their young,” Chaney said. Females who are not of reproductive age will form their own distinct roosts, he added.
At La Honda Creek Open Space Preserve, MidPen staff recently completed work to repair and stabilize the historic White Barn. Townsend’s big-eared bats and long-eared myotis were known to roost in the structure, so staff added roosting cavity structures for the bats.
When the Townsend’s big-eared bat was spotted in the abandoned house at Tunitas Creek Beach, a specialist was consulted to establish whether or not the structure was a maternity roost. It was not, but when dried-up guano – likely belonging to yuma myotis and the big brown bat – was found on-site, experts realized the bats were likely using the space to sleep for the day while foraging in the area at night.
To support the bats, a universal roost, one that is used by both male and female bats of different species, was constructed nearby. Staff plan to monitor and survey it and consult with experts to learn more about how to support local bat populations.
“This is just the beginning,” Cole said. “I think this will all inform our ability to improve our understanding of the bat community in our parks and how we can protect them.”
To learn more about local bat colonies, visit openspace.org/where-to-go/nature/bats.
More stories about Silicon Valley’s animals:
–Santa Clara Valley Bird Alliance celebrates a major milestone with a month of free avian activities
–As the sun sets, these Peninsula preserves and landmarks come alive for guided walks
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