Media & Education
BATS Magazine

Volume 16, Issue 3, Fall 1998

Hidden Housing - Artificial Bark for Bats

A stroke of inspiration at a BCI workshop led two biologists to develop a new form of artificial roost that seems to be meeting bats' approval . . .

By Noteman, Laurali

A stroke of inspiration at a BCI workshop led two biologists to develop a new form of artificial roost that seems to be meeting bats' approval . . .

By Laurali Noteman

Just before dawn, with camera in hand, I headed to the quiet pond that lay below our campsite. There, a stoic old pine snag cast its reflection in the shallow pool, perfect for a photograph at sunrise. On the way back to my tent, I ran across a piece of white nylon netting draped loosely around the base of a ponderosa pine. Though curiously out of place, it didn't seem to be discarded or unintentionally thrown. About 30 feet up the ponderosa's massive trunk, I saw another oddity--a patch of bark that looked somewhat brighter than the bark around it. When my husband saw it, he was as perplexed as I.

The following weekend we returned to the same area to camp with friends. "Hey June, come here a minute, look at this," I hollered.

"Oh, that's Bat Bark," she stated, as if it were something everybody knew about. June works at nearby North Kaibab Forest Ranger District in Fredonia, Arizona, and she has inside information. When I asked her more about the strange bark, she gave me the names of two North Kaibab biologists to contact: Dan Garcia de la Cadena and Melissa Siders.

Before Garcia and Siders went to a BCI Bat Conservation and Management Workshop in 1994, neither of them knew much about bats. "It was an action-packed week," Siders recalls. "I learned how to mist net and identify different species." While they were there, Garcia had what he thought was a harebrained idea to create artificial bark roosts, but BCI Executive Director Merlin Tuttle was supportive. By the time they left the workshop, Garcia and Siders had a pretty good idea of what they wanted to do.

Back at work doing surveys in the Kaibab National Forest, Garcia came up with a way to create Bat Bark. "It gets pretty lonely out there," he explains. "You have a lot of time to think."

Garcia knew the attributes of a good roosting place, and he had a friend who knew how to make molds. "I put an actual piece of bark on some cardboard, and put spacers on that," he says. "The spacers are designed to keep the bark away from the tree." Then he sent the prototype to his friend, who made a mold and cast the first pieces of artificial bark out of polyurethane foam, similar to that used to insulate homes.

The purpose of Bat Bark is to give bats more roosting options. Crevice-roosting species often find shelter under the loose bark of dying trees (snags). But such trees are scant in many forests today because of a mistaken past belief that they can propagate harmful insects if not removed. A tree of most any age, however, can create a secure, long-term dwelling for as many as 100 bats with a two-foot by one-and-a-half-foot section of Bat Bark attached to it.

"What's neat," Garcia spouts enthusiastically, "is that with Bat Bark, you don't need a snag to have the proper characteristics for a bat roost. And while loose bark on a snag may last only four to seven years, Bat Bark may have a life span of 30 to 50 years."

Bat Bark doesn't stick out like a sore thumb, either. It blends into the tree, so aesthetically, it doesn't interrupt the view. In fact, I would never have noticed the piece near my campsite had Garcia and Siders not left the nylon netting underneath. I soon learned the purpose of the netting: to catch bat droppings, which tell researchers whether bats are using the artificial bark.

As with bat houses and other artificial roosts, internal temperature is a major concern for Bat Bark. To get an idea of what temperature differences there might be between the Bat Bark and natural bark roosts, Siders and Garcia first had to find natural bat roosts in the vicinity. Fortunately, the necessary netting and tracking skills were precisely what they had learned at the BCI workshop. After trapping bats with mist nets over small stock ponds, the biologists attached tiny radio transmitters to the bats' backs and tracked them back to their roosts. When they found long-legged bats (Myotis volans) roosting in snags, they placed matchbox-sized, battery-operated temperature data loggers called thermisters inside the snag roosts, then also placed them in the artificial bark roosts. After about a month, Siders removed the thermisters and looked at the data. Their Bat Bark roosts had essentially the same temperatures as the natural roosts.

"But when you find an answer, it just triggers more questions," Siders remarks. In the fall of 1997, after a year with 24 Bat Bark roosts in place, there were many additional factors to consider. The collections of bat droppings on netting showed great news--about a third of the 24 barks had been used, some multiple times. But it was clear now that natural bark roosts differed from the artificial bark in several ways: the natural roosts had more canopy cover, they were significantly closer to the ground, and they mostly faced southwest. Further, the polyurethane foam bark was too thick and inflexible. It was time for some changes. Garcia and Siders made 16 new models from fiberglass, planning to alter their placement according to what they had learned.

I met with Siders, her husband David Sinton, their five-month-old son, Aaron, and wildlife technician Becca Steffenson early one fall morning and headed toward Jacob Lake, Arizona. Siders had been out to the site earlier in the month and located trees suitable for their needs: near water, relatively free from other growth, and with few or no dead branches to hamper the installation.

Sinton and Steffenson installed the bark while Siders served as ground crew. I was impressed with this trio. They communicated their needs, each asking the others for suggestions or approval. Together they figured out how to climb 20 feet straight up a tree carrying a cordless drill, washers, a dozen deck screws, a caulking gun, and a piece of Bat Bark. When the two climbers reached the 20-foot mark, they mounted the Bat Bark on the southwest sides of the trees, sealing it across the top and upper sides with silicone. A half-inch piece of polyvinyl chloride (PVC) was used as a spacer at the bottom of the bark to ensure a given distance between the actual bark and the fake bark to allow easier entrance for the bats.

"We've found that the pieces bats are using have a little wider opening at the bottom," Siders commented as she prepared the PVC.

Back at the ranger station, Garcia voiced a few concerns. "We've had our doubts. Do the bats really see the Bat Bark? Are they able to recognize it? If they use it, will they return next year? We think that the bats may crawl and fly around a tree checking things out, looking for cavities. I know that some birds do that when they're looking for the perfect cavity."

The report for the summer 1998 field season indicates that bats are indeed finding and using the bark. Use this year for the polyurethane models was up to 42 percent, and the 16 new fiberglass models had 24 percent usage. These numbers are encouraging; in fact, they compare favorably to data on newly erected bat houses. Reports from BCI show that approximately half of bat houses aren't occupied by bats until after their first season in the field, so it seems reasonable to expect that Bat Bark will likewise attract more bats over time.

Unfortunately, the bats' patterns this summer showed no clear preference between the fiberglass or polyurethane roosts, nor among particular sites. Bats returned to some, but not all, of the same barks they used last year, and in addition began using some barks not used the year before. The effort to decipher these preferences will continue next summer, along with a more high-tech effort to monitor roosts. By placing a small bat detector with a voice-activated tape recorder at one of the bark sites, the Kaibab team will be able to analyze recordings of bat calls on their computer to tell whether bats are visiting the roost, which species, and at what time(s).

While the roosts are vacant this coming winter, the biologists will download and analyze data from the thermisters. Siders will also take time to write grant proposals and look for other forms of assistance for the project, such as equipment or volunteers. The only Bat Bark in use during these months is at the Kaibab Visitor Center, where rangers take advantage of the attention-getting prop to help teach visitors about the importance of snags and bats. In coming years, I won't be surprised to find more hikers and campers like me looking up into the trees trying to spot a sample of these unique additions to the forest!

Laurali Noteman is Director of Human Resources at Kane County Hospital in Kanab, Utah. She and her husband enjoy horseback riding and camping in the remote areas of northern Arizona and southern Utah.

Bat Bark Copyright © 1996, Dan Garcia de la Cadena

Funding for the Bat Bark project came from Bat Conservation International's North American Bat Conservation Partnership, the Arizona Game and Fish Department Heritage Grant, the National Forest Foundation, Max McGraw Wildlife Foundation, and the Kaibab National Forest Challenge Cost-Share Program.

For a complete report on the development and testing of Bat Bark, write to Melissa Siders at:
USDA Forest Service
North Kaibab Ranger Station
P.O. Box 248
Fredonia, AZ 86022
or via e-mail at Siders_Melissa/

After hauling their gear and a piece of fiberglass Bat Bark 20 feet up a tree, David Sinton and Becca Steffenson secured the artificial bark with deck screws and silicone. The flexible Bat Bark material will fit a wide range of tree sizes and can be adapted to mimic a variety of trees across North America. Other land-management agencies have begun testing the idea as well, with modifications for the bats and trees of their regions.

Bats roost between the tree trunk and the bark in this ponderosa pine snag. Although a snag may last many years, the loose bark that makes an ideal bat roost does not. By the time a sufficiently large piece of bark separates the necessary one inch from the trunk, it often falls off within one to three seasons.

The long-legged bat is just one of 12 species of tree-roosting bats on the Kaibab Plateau that may be using Bat Bark. Once field testing is complete, Bat Bark could meet the needs of close to half of all North American bat species.

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