A few hours on a bat capture-and-release operation in Big Sur reveals new information about the flying mammals of UC’s Big Creek Reserve.
by Samantha Chavez
Oct. 22, 2015—They flit across forest canopies in such dim light you’re likely to miss them. But with the right equipment, you may be able to catch some. UC-Santa Cruz researcher Dr. Winifred Frick and her research partner Paul Heady have brought just that. I join them at the UC Big Creek Reserve in Big Sur on a quest to catch some local bats.
The range of bat species living on the Big Creek reserve hasn’t yet been well documented, and catching some individuals is the best way to find out which species call the reserve home. This way, reserve managers can protect their nocturnal neighbors. As the sun sinks lower in the sky, we prepare tonight’s bat-catching setup—mist nets.
Mist nets are finely woven nylon nets stretched out between two poles. When they’re set up they almost looks like volleyball nets. After we set up the first net, it begins to disappear from my view as I step farther and farther away. It’s almost impossible to see from a few feet away, especially in the dimming light. Its fine spider web netting is fragile and known to be torn by hapless hikers, bikers, or drivers unaware of its presence.
We set four nets up: two stretch over a river and two more over a road. It may sound like a strange place to put up nets, but like any other animal, bats like to take the easiest path from point A to point B. Flying through the branches of forest canopy can be hazardous. Why should a bat fly through so many obstacles when it can go over a conveniently cleared-out road instead? The spots chosen on the road and the river are placed in area where the branches dip lower than the rest. When a bat is flying over the relatively clear road and suddenly encounters a tree branch the bat must decide to fly above it or below it. Those that choose to dive beneath the branch are caught in the mist net. It takes an experienced mind to find the right locations to set up nets, thankfully, Frick and Heady have been doing this for decades.
Catch of the Night
Right as sunset is starting, we get our first catch. But it’s not a bat. It’s an American Dipper heading home for the night. Dippers are dark gray birds that swim under water in search of aquatic insect larvae. It squawks angrily at its captors as it is slowly untangled from the net unharmed. Mist nets are used to catch birds in flight as well as bats, but a big difference between catching the two is that bats will chew through the fine string, leaving gaping holes in the sheer black netting. Because of this, it’s imperative to check the nets regularly, but not so much that we nosy scientists scare the bats away from the nets.
The first bat we catch is a Myotis californicus, also known as the California myotis. It’s smaller than the palm of my hand, and its fur is a dull brown color. It twitches in the net once or twice as Frick begins to carefully disentangle it. She helps graduate student Andrés Muñoz delicately remove the bat from the net. Fingers work carefully around the bat as if dismantling a bomb. Both the bat and the net need to be left unscathed. Muñoz deftly plucks strings and gently pulls on the little bat until the net falls away, and he is left clutching a tiny animal in his hand. The bat is placed in a small cloth sack as it is transported from net to a nearby picnic table. Frick’s gloved hand softly but firmly holds the Myotis and raises it up for all to see. Right next to its foot, on the webbing between the leg and the tail, is a small cartilaginous spur called a calcar that helps hold the tail membrane out when catching insects, like a batter’s mit. The calcar on this bat has a small flap of skin, which makes it something called a keeled calcar. The presence of the keeled calcar, color of its fur and overall face shape lead Frick to determine that it definitely is a Myotis californicus. From afar, many Myotis look similar, and it is sometimes only these small details that let scientists tell certain species apart. They may be small, but Myotis eat plenty of insects and they play an important role in the ecosystem by consuming nocturnal insects. Other bat scientists have recently discovered that in the Midwest, bats save farmers billions of dollars by reducing crop damage from insect pests.
Here on the California coast, catching a bat this early in the night is a big confidence-booster for a good night of bat-catching. More net checks bring out more bats, another Myotis—this time a Yuma myotis (Myotis yumanensis). As we place the bat into the bag and do another round of net checks, we hear shouts of excitement coming from the river.
I watch from the riverbank as Frick removes the bat from the net. She brings it over to our base camp, the picnic table. It’s a Western Red Bat, Lasiurus blossevillii, and it is larger and angrier than the smaller Myotis bats. It has thick red fur along its body and even has fur extending on its wings. It struggles and screeches in Frick’s hand for a few minutes before calming down. She explains that these bats hang out in the leaves of trees, whereas the Myotis roost in tree crevices or caves and buildings. Because red bats roost exposed in the leaves of trees, they are more likely to be attacked by predators and are therefore feistier and more likely to struggle against capture. It’s an amazing catch; they’re not too common and they’re harder to find, since they don’t form large colonies that researchers can find during the day. As the night continues, we catch another Western Red Bat, as well as a Fringed myotis and another California myotis. In total, over five hours, we catch eight bats and four species—a successful night, but it must come to an end.
When it’s time to release the bats, Heady prepares to record their ultrasonic echolocation calls as they fly away. It will be used in a computer program that will match bat call records to the species the call comes from and help build a library of what the echolocation calls from these different species sound like. The bats are kept warm and snug in the cloth bags. Frick gently pulls a Myotis out with a gloved hand and holds it in a loose fist. She opens her hand, and the little bats take a few hesitant flaps before gaining momentum and flying away, echolocating into the night. Heady chases after them to record their calls as they flutter away from the light of our headlamps. In one instance, a little Myotis wasn’t yet ready to fly. Although bats are mammals and warm-blooded, because they are so small they can turn their body thermostats off and just “go cold” to save energy. A few minutes warming up in Dr. Frick’s shirt and the bat is able to take off without hesitation. The bats will spend the rest of the night eating insects as we take down the nets and pack up the car.
Not So Scary After All
As we sleep, these small animals, the only true flying mammals, are busy eating nocturnal insects and fulfilling their role as nature’s pest control. The public hasn’t always had the best relationship with bats. Some people find them a little scary. Maybe this is because they remain mysterious creatures of the night. Very few people ever get to see these delicate winged balls of fluff peering at you with curious eyes. East of the Rockies, bats are dying in droves from an introduced fungal pathogen that causes a disease called White-Nose Syndrome in bats that hibernate in winter. Bat biologists worry about what will happen to bats in western states as the fungus continues to spread out west. Without natural pest control, California’s agriculture could suffer if our bat populations crashed. In the meantime, scientists like Frick are learning as much as they can about White-Nose Syndrome, as well as about bats in general, in order to help protect and save our nocturnal neighbors.
Take the time to hike the woods around sunset and keep your eyes sharp.
You may see a few dark shapes flit through the sky, eating insects and playing their important part in the ecosystem.