Into the Dark – A Night of Bats

Under a blanket of stars, we waited in a circle, straining our ears for any chirping sounds. Wildlife Biologist Lance Carpenter took a look at his watch. “It’s probably about time,” he said.

Wearing waders and lots of bug spray, Lance, fellow bat Biologist Heather Halbritter, several other CPW staff, and I were going out every 15 minutes to the river below us hoping to catch a specific nocturnal animal: a bat.

Solving Bat Mysteries

While most of us were there to document and help out with bat research, Lance and Heather have been working on this project for several years. The two of them go out almost every day through the summer and fall seasons to catch, record, outfit, and track bats at Castlewood Canyon. Oftentimes their work extends from the late hours of the night into the wee hours of the morning as they wait for opportunities to fit more bats with transmitters– their method of tracking and documenting the animal’s behavior.

Bats are not little-known animals – afterall, they’re a favorite Halloween costume, they inspired the design of one of our favorite superheroes, and they dart through our summer night skies in distinctively erratic flight patterns. But what we do know about them is very little. That’s why specialists like Lance and Heather are fascinated by them. There’s still so much we have yet to discover!

For example, biologists have only begun to understand how and why bats choose specific areas for their maternity colonies (temporary groups formed by female bats to have their pups). “Bats will form a maternity colony somewhere year after year, and then stop using that location and go somewhere else. But then, years later, sometimes they come back,” Lance explained. “We don’t know why they leave a particular maternity colony and then come back to it.” Biologists haven’t discovered very many maternity colonies to begin with in Castlewood Canyon- only six are currently known.

There’s also quite a bit of mystery surrounding bats’ roosting sites- the places they go to hide in during the day (day roosts) and to rest between feedings during the night (night roosts). “Some of the things bats might be looking for are specific microclimates where the temperature and humidity are just right. But we really do not have a good handle on why they select specific day and night roosts,” Lance said. “Right now we’re trying to develop a database to gather research from other scientists. It’s an ongoing process.”

Why It Matters

Answers to these habitat use questions are being asked by bat experts around the country, not just in Colorado, but there’s a reason why Lance and Heather have been focusing their research on Castlewood Canyon- and why that research is important. “The park has become a big mecca for climbers,” Lance told us. “We want to know if the bats are selecting away from climbing routes, specifically bolted and top rope, and if there are any maternity colonies along the routes.”

That’s why Lance and Heather have been collecting data about day roosts in the park, measuring the features of the cracks they’ve tracked bats to- their dimensions, what they look like, their distance from the rim of the rock face, if there’s anything in their way, etc. “It’s really important for the park managers because then they can say, ‘Hey climbers: we want to avoid this area.’” Lance explained. Their research may also help direct the Climbing Board’s decisions when it comes to setting up new climbing routes at Castlewood Canyon to avoid maternity colonies.

The Unpredictable Work of Bat-Catching

While Lance and Heather have been exclusively studying dayroosts (and maternity colonies), most of the actual work they do happens at night. That’s why five other staff members and I met them at the park right as the sun was setting.

As someone who was unfamiliar with field research, I wasn’t sure what to expect from a night studying bats- certainly trying to catch them with nets was far from my mind. But after hiking down to the riverbed, that was exactly what we set out to do. Splitting up into smaller groups, we waded through the river, setting up pairs of poles across from each other to string four different nets across the river at about 100 ft intervals. “Mist nets”, as they’re called, have tight enough weave to catch bats flying into them, but loose enough weave to make them less detectable. They’re also divided into horizontal sections sewn together in such a way that they leave pockets for the bats to fall into.

Ideally, the mist nets are checked every 15 minutes; hopefully, the bats get caught by hitting the nets, then falling immediately into the pockets; and hopefully, they stay stuck in the nets until you check on them. But if there was one thing I learned about bat-catching at night is that it can be elusive and tricky work.

For one, it’s entirely possible to catch nothing. Our team waited a couple of hours for anything larger than a moth to get stuck in one of our nets. We chatted for a while, trying not to get our hopes up when we thought we heard any chirping or chattering noises, then fell silent. We sat so still for so long that the neighborhood muskrat decided to swim up to the river’s surface and say hello. Finally, after making one of our routine checks, I heard Rachel’s joyful call: “Caw-caw!” (code for “We caught one!”)

Second, a lucky bat will occasionally escape from the netting. Sometimes it squirms its way out, and sometimes it chews its way through the strings. While we did eventually start catching bats every 15 minutes, several of them managed to escape during the time it took for Lance or Heather to get to their specific nets.

Lastly, sometimes the bats that do hit the nets do not fall into the pockets, but rather get tangled in the netting. Our first bats found themselves exactly in that predicament. Thankfully, Lance and Heather have years of experience untangling bats with astounding gentleness and patience, leaving them unharmed.

Those of us who were new to the bat research process watched them, mouths-gaping, as they used crochet hooks to carefully unhook each string from around the tiny feet, fingers, and edges of the bats’ wings. The bats hissed, squirmed, and bit their gloves (only Lance and Heather had gotten the required rabies shots for handling bats), but they held on firmly, making sure the bats didn’t tangle themselves further.

Tracking and Learning From Bats

Once the bats were untangled, they were observed and their species and sex was identified. While Lance and Heather’s research initially began with the rarer Townsend’s big-eared species of bats, they didn’t have much luck catching any in Castlewood specifically, so their research has focused on the little browns and fringed myotis. While both of these species are fairly common, they are lesser known than the big browns and stand to benefit from their research. If Lance and Heather happen to catch any bats of these two species (we didn’t have our luck that night), the intricate work of fitting them with transmitters begins.

Lance and Heather fit the little browns and fringed myotis with what are called “VHF (very high frequency) transmitters”. These transmitters do not function by GPS, but rather by sending wave frequencies to a separate Yagi antenna. “What’s nice about that antenna is you can pinpoint exactly where that transmitter is,” Lance said. “You can take the cable off of it and stick it right down into a crack. The closer you get, the louder it gets.”

While going out during the day to track transmitters’ signals is not ideal after a long night, the VHF transmitters are the best option at the moment for bat-tracking. “We have this 5% rule. So if the transmitter or collar we put on an animal is greater than 5% of their body weight, it’s not good,” Lance told us. Currently, GPS collars are way too big and heavy to be used on bats. “We don’t have the technology to shrink it,” Lance explained.

The VHF transmitters that Lance and Heather use are tiny, smaller than a fingernail. Before being fitted to the bats, each one has to be hand-soldered and wired to start signaling and then waterproofed by dripping wax from a candle. Then, transmitters are attached to the bats’ backs by using Perma-type, a kind of glue. The glue works well for tracking bats because, as Lance explained, “it’s a great adhesive- it lasts for about three weeks on the bat and then the transmitter just falls off.”

The Best, Unlucky Work Day

While we unfortunately didn’t catch any little browns or fringed myotis that night or place any transmitters, it was still an eye-opening experience for many of us on the team. We were grateful to Lance and Heather for giving us the opportunity to see creatures that you rarely get to observe up close!

And we did, afterall, manage to catch a few bats that night. The team favorite was a particularly spunky bat- a beautiful, hoary bat  (another species at Castlewood Canyon) that we decided to call “Jorge”.

That night, we all left in a cheerful mood, laughing our way back up the trail as we joked about our new friend Jorge the hoary bat.

Bat Week is celebrated every year from Oct. 24-30. To learn more about Bat Week and the fascinating creatures that inspired it, visit the CPW website.

Written by Olivia Baud. Baud is a Communications and Media Intern for Colorado Parks and Wildlife.