Tales from a Summer Night of Bat Research by Redwood Creek

By Science Communication Assistant Jailyn Hoskins, San Francisco Bay Area Network Science Communication Team

Just watching the monitoring team gather information from these bats was interesting. In just a few minutes, they’d check a bat’s reproductive status, measure it, assess its age by examining its wing bones in front of a headlamp, and collect swab and tissue samples.

NPS / Environment for the Americas / Jailyn Hoskins

October 2022 - One of my favorite places to spend time this summer was along Redwood Creek in Muir Woods National Monument. Even in the dry season when the water levels were low, the sounds of the water flowing were always so peaceful. On one memorable nighttime visit, I met with several National Park Service and US Geological Survey biologists to learn about and photograph their bat research. Turns out it’s a good place to catch bats that like to hunt along the creek for mosquitos, flies, and beetles.

In the last few moments of sunlight, we set up four mist nets (loose mesh nets that are practically invisible when strung up) over different parts of the creek and crossed our fingers that we would catch some bats. The previous night the team had only caught one at the very end of the night, so our hopes were not high. But surprisingly, we didn’t have to wait long for our first bat. I let everyone know that I was the good luck charm.

In the last few moments of daylight, we set up four mist nets over different parts of the creek and crossed our fingers that we would catch some bats.

NPS / Environment for the Americas / Jailyn Hoskins

There are ten bat species found in Muir Woods, and the three small bats we wound up catching that night were all California myotis. I had never seen a bat that up-close before. They were so interesting to watch, and it felt like I was in a sci-fi movie seeing their fangs.

Just watching the monitoring team gather information from these bats was also interesting. In just a few minutes, they’d check a bat’s reproductive status, measure it, assess its age by examining its wing bones in front of a headlamp, and collect swab and tissue samples. If the female bats had been large enough, the team would have also attached temporary radio transmitters to determine what habitat features they are using as maternity roosts. In the end, the team was only able to deploy one radio transmitter this year for all their nights of mist netting—on a big brown bat, which they couldn’t relocate the next day. They’ve had much more luck radio tracking bats in years past.

It was also funny to see the biologists get excited to find bat poop that they could collect. These fecal samples would later be used along with the swabs and tissue samples to check up on the bats’ health. The team is on high alert for signs of white-nose syndrome, a disease that has been devastating bat populations across the country. So far, it hasn’t been found in the San Francisco Bay Area.

In the time in between processing each bat, USGS Biologist Gabe Reyes showed me a bat detector he had set up nearby.

NPS / Jessica Weinberg McClosky

In the time in between processing each bat, USGS Biologist Gabe Reyes showed me a bat detector he had set up nearby. With a special recording device atop a tall pole, the acoustic detector records the calls of different bat species. Software helps researchers identify the calls to better understand the presence and activity of various species in the area. At the time we checked on it, it had just identified a high-flying Mexican free-tailed bat in the vicinity. This tool is important because it allows for different species to be recorded that wouldn’t be caught in low-hanging nets.

Biologist organizing the evening's data.

NPS / Environment for the Americas / Jailyn Hoskins

Bats around the world provide us with valuable services such as pollination, seed dispersal, and predation of insects. In Marin, all of our bats are insect-eaters. The various natural features of Muir Woods, including redwoods and Redwood Creek, make suitable roosting and foraging habitat for numerous bat species. By studying which species of bats use habitats in Muir Woods—and how they use them—bat monitoring helps the National Park Service conserve bats in the area, many of which are species of concern.

For more information

• One Tam Bat Monitoring webpage
• USGS Bat Research in California webpage
• Pacific Coast Science and Learning Center Bats webpage
• Learn more about bat conservation in the San Francisco Bay Area
• Contact Wildlife Biologist Katie Smith

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