ON THE TRACK OF FOREST BATS

A cooperative study in northern Arizona yields some extraordinary surprises about where forest bats roost and, in turn, will significantly change how forests are managed for bats . . .

by Mari Murphy

The bat confounded a whole team of researchers. They had affixed a tiny radio transmitter to its back and were attempting to follow the signal back to the bat’s roost deep in the Coconino National Forest in northern Arizona. Rick Miller, an expert radio tracker and a habitat specialist with the Arizona Game and Fish Department, had picked up the signal from a fixed–wing aircraft brought in to speed up the arduous process of locating the bat over rough, forested terrain. Once he zeroed in, the ground crew had to hike only about 200 yards to follow the loud, highly directional signal. Confident that the bat was close at hand, they entered an area with large, old Ponderosa snags, just the sort of place they would expect to find a bat roosting. Then the signals abruptly faded.

They were participating in the first comprehensive study to quantify the habitat characteristics of forest bat roost sites in Arizona, a project that was jointly initiated and funded by BCI, the Coconino National Forest, and the Arizona Game and Fish Department. Heather Green, a biologist with the Coconino National Forest, and Tom Morrell, a Heritage research program supervisor with the Arizona Game and Fish Department, served as co-principal investigators, while BCI member Bert Grantges of Arlington, Texas, acted as field coordinator. Merlin Tuttle provided technical advice during the early field work. Three BCI members, Kei Yasuda of Eugene, Oregon, and Elaine McCann and Rob Sinton of Belvidere, New Jersey, volunteered for the four-week project last summer, providing invaluable field assistance.

The day before, they had placed the radio transmitter on a long-eared myotis (Myotis evotis), one of 11 species believed to be in the study area. The transmitter, which weighed less than a dime, was glued between the bat’s shoulders with a special surgical adhesive, allowing the device to drop off naturally in a week or two. Until this study, only anecdotal information existed on where forest bats like these roosted. Long-eared myotis were known to roost occasionally in caves, mines, cliff faces, or buildings, but little was known about their requirements for rearing young.

Trying again to pick up the now faint signal, the team turned away and circled the snags, looking upward, when suddenly the transmitter pulse peaked with deafening clarity from behind them, so loud, in fact, that they tore their headphones off. But no sooner did they head back toward the sound, than it again faded. Over and over the signal came back loud and clear, but when they tried to get a fix on the exact location, it became faint. What was going on?

After reviewing the situation, the team suspected that something was wrong with their receiver and sent back for another. But even with a new one, the results were the same, and the location of the bat continued to perplex them. Kei Yasuda and Tom Morrell commented that when the signal faded, it seemed to be coming from the ground rather than up in the trees. Had the bat lost the transmitter? To find out, they took the antennae off the receiver and slowly trailed the cords on the ground.

Frustrated, Merlin Tuttle looked down, his eyes searching the forest floor. Just then, in a small rock crevice beneath his feet, a glint caught his eye. It was the reflector-tape-covered band they had placed on the bat’s forearm when they had tagged it. No wonder the signal was fading. Every time the bat saw giants tramping the ground toward its crevice roost, it retreated to safety down into the crack. As they moved away, it surfaced to see what was going on. Hoping to catch it in the act, the team slowly backed away this time, keeping their eyes on the crevice. The bat’s long black ears gradually emerged, followed by the bat itself. For a moment, they all looked at each other in mutual astonishment. Merlin and Kei stood about 10 feet on either side of the small bat, watching its ears sticking up out of the dark crack. Like two miniature periscopes searching for danger, the bat’s ears switched back and forth a full 180o, listening first to one and then the other as they each spoke.

Only one other North American bat is known to roost in the ground, the western small-footed myotis (Myotis ciliolabrum). What the team would discover is that pregnant female long-eared myotis roosted predominately alone in these solar-heated rock crevices and in logs. They then would move to small nursery colonies in fallen logs or snags to give birth and raise their young. These ground roosts were the first such documented sites in Arizona and certainly were not what researchers expected to find. It was only one of many surprises.

The idea for the cooperative project rose out of a two-week preliminary survey BCI conducted in the area in 1992. When Merlin Tuttle reported to local Forest Service managers that bats which had been seen in abundance some 20 years before now appeared to be uncommon, there was strong interest in learning more. No intensive studies had ever been conducted on the ecology of insectivorous bats in forest habitats in Arizona. Their status and current threats were unknown, and essentially nothing was known about the type of roosts bats use in state forests.

National forests live up to their slogan, “Land of Many Uses.” They are one of our most intensively managed habitats, encompassing recreation, logging, grazing, and mining. They are also among our most biologically diverse lands, providing critical habitat for a wide range of animals. Over the last decade, growing concern about environmental quality has prompted Forest Service managers to reevaluate management strategies and reduce timber harvest levels to favor wildlife and retain old-growth forest. Although logging continues to decline steadily, especially in recent years, our national forests still provide about 18 percent of our nation’s softwood lumber.

The more managers know about the plants and animals that make their homes there, the more they are able to take the needs of these native species into consideration in forest harvest plans. In the case of bats, almost nothing has been known of their value to healthy forests. The result of this lack of knowledge is that bats are largely overlooked when forest management plans are developed. A study, therefore, was timely and will have broad applications for forests in other parts of the country.

The Coconino National Forest is one of 156 forests in our National Forest System. Encompassing some 1.8 million acres, it is rugged and beautiful country, predominately ponderosa pine and other conifers. The forest is home to a great variety of animals, from elk and mule deer to bobcat, black bear, and many others. Although seldom seen by the many visitors, bats comprise about 20 percent of the mammal species in the Coconino.

The research area, just north of Flagstaff, skirted the slopes of the San Francisco Peaks, which include the state’s highest point at 12,633 feet. The study was conducted at elevations between 7,300 and 8,400 feet. The Forest Service provided logistical support, vehicles, and radios, and the Game and Fish Department contributed radiotelemetry equipment and an airplane once a week to facilitate tracking. BCI recruited volunteers for the project.

Days were warm, but even in early summer, nights–when much of the research was conducted–were cold and often freezing. Volunteers had been told to prepare for anything from intense sun to rain and hail, and to bring a range of clothing from shorts and T-shirts to down jackets and wool hats. They had to be in excellent physical condition to hike long distances over difficult terrain, and they had to be willing to work day or night. The reward was to discover things about bats that no one had ever known before, along with the knowledge that their discoveries would help shape future forest management practices for bats.

Over the four weeks of the study, the team tagged 18 bats from five species. All were tracked back to a roost, a 100 percent success rate–perhaps a first. Ninety percent were located with the help of the aircraft; within 48 hours the team had found the roosts of four of the five species, and all five within the first week. Besides the long-eared myotis, they also tagged fringed myotis (M. thysanodes), long-legged myotis (M. volans), Arizona myotis (M. occultus), and Allen’s lappet-browed bat (Idionycteris phyllotis). The Arizona myotis is a candidate for federal endangered species listing and is a U.S. Forest Service Region 3 sensitive species. All but one of the tagged bats were female.

In addition to the surprise of finding long-eared myotis roosts close to the ground, another major discovery was learning where lappet-browed bats raise their young. They had tagged a female, but even from the plane, they hadn’t heard her signal. Then Rick Miller flew low past a likely cliff; the transmitter signal was loud and clear. Spotting a deep crevice in the rock, they surmised that she might be there. It would be a long hike, however, and it was high on the mountain, so they called off the ground search for the time being.

A few days later, Merlin Tuttle and Bert Grantges decided to make a day of it. Bert covered the valley while Merlin patrolled the ridge. Once in a while they heard faint signals, but the direction was unclear. After walking for miles, they found the crevice they had identified from the plane; it was far too deep to find the bat, and in any case, there was no signal. Giving up, they returned to base camp.

A week later, standing in camp, Kei Yasuda picked up the bat’s signal loud and clear. This time it was coming from the mountain directly above them. Excited, he followed the signal up the slope. The tagged bat, along with about 40 others, was roosting in an old Ponderosa snag. What appeared to have happened in the week gone by was that she had moved from her cliff roost to her maternity roost a few miles away over a ridge. The faint signals they had heard when they searched for her on foot likely had been distant bounce-off from the mountain. Prior to the study, these bats were believed to be strictly cave and mine dwellers. The maternity colony discovered is the only one known in Arizona for lappet-browed bats.

All of the bats they followed back to their roosts reared young in Ponderosa snags that were anywhere from 150 to 300 years old, remnants of old forest. Stands where the roosts were found varied. Some were dominated by saplings, others by trees five to 12 inches in diameter, and still others by old growth. Many roost stands showed little evidence of timber harvest, but some had historically had tree removal as well as more recent activity.

During the course of the study, it became very clear that, while bats will roost in a younger forest and even in logged forests, multi-age forest is essential if they are to stay and reproduce. If multi-age stands, including old growth, are not left, the dead and dying trees that the bats depend on will not become available on a continuing basis. These durable snags stand for a long time, providing habitat for bats and many other creatures of the forest, sometimes for as long as 50 years or more. In the past, forestry practices and logging contracts have often called for the removal of such trees.

In summing up the first season’s work, Heather Green affirmed that the information gained in this study “will help make some significant changes in how forests are managed for bats.” Furthermore, the new data will be entered into the Arizona Game and Fish Department Heritage Data Base and will also be used for updating Gap Analysis statistics.*

Because the bats were netted and tagged at four different sites in the Coconino National Forest, in or adjacent to sensitive old-growth forest, the data will provide a fairly complete picture of Arizona’s forest bat fauna. This summer the study is continuing with netting planned for six more sites. The project will be expanded to investigate and compare roost site characteristics not only in the pine and mixed conifer habitats from last season, but also in pine and oak habitats and in a more managed forest.

With this information, resource managers will be able to make informed decisions on how Arizona’s bats and forests should be managed to their mutual benefit; in turn, other states can look toward Arizona as a model for future management.

(Bio)
Mari Murphy is editor of BATS.

(Footnote 1)
* The Gap Analysis Program (GAP) was initiated by the U.S. Fish and Wildlife Service in the late 1980s and aims to identify, region by region, the gaps in protected lands or species. Using computer technology to sort the massive amount of data, GAP identifies individual animal and insect species and plant communities that make up the biological diversity of a geographical region. Biologists then can discern which pieces of land would best serve biodiversity protection. Thirty states now use GAP as a long-range planning tool.