by Ronnie Sidner
"I would very much like to see the bats return to Colossal Cave. From an economic standpoint, I think it would promote use of the cave. I know I would be much more apt to go out there if I would be able to see bats."
Tucson housewife and community volunteer, June Hirsch, offered this statement to the Pima County Parks and Recreation Commission in Arizona at their monthly meeting in June. I had just presented a proposal about making Colossal Cave hospitable for bats again, and the chairman asked the attending public for comments. Sincerity doesn't make it any easier to speak up in public, but I wasn't surprised. A couple months ago June had asked me if I could find some bat guano to "seed"her bat house. Volunteer work with the Audubon Society had led her to bats and BCI. She had heard me explain about the need to protect bats and their habitat and decided to become involved.
In recent years, several causes for declining bat populations have been suggested. Many researchers now think that habitat destruction, especially loss of cave roosts, is the primary factor [see "Who's Endangered and What Can We Do?"in this issue]. For the past few years, I've been locating old roosts in southeastern Arizona, and I agree that habitat loss may well be the major problem here. One unfortunate example is Colossal Cave.
Colossal Cave is a state-owned, county-leased concession that attracts over 50,000 visitors per year. Located 30 miles southeast of Tucson, this natural limestone cave is hidden in the foothills of the Rincon Mountains within five miles of Saguaro National Monument. Surrounding countryside climbs quickly from Sonoran desert scrub to an 8,000 foot peak. Seventeen species of bats have recently been recorded in the protected wilderness of this small mountain range, more than most U.S. states have within their entire borders. But such attractions are not without costs. Arizona's human population has grown from 750,000 to 2.7 million since 1950 and is expected to reach seven million in the next 20 years. For a diverse bat fauna (four families and 28 recorded species) inhabiting once-remote areas, essential roosting sites are rapidly being destroyed and some already have been lost.
In 1953, Professor E. Lendell Cockrum of the University of Arizona began studying the bats at Colossal Cave. He recorded five species: Sanborn's long-nosed bat (Leptonycteris sanborni), the Mexican long-nosed bat (Choeronycteris mexicana), the California leaf-nosed bat (Macrotus californicus), the Cave myotis (Myotis velifer), and Townsend's big-eared bat (Plecotus townsendii).
Populations of Townsend's big-eared bats have decreased in several states [BATS, December 1988, February 1985]. The Cave myotis occurs in large colonies in a limited number of western states: Kansas, Oklahoma, Texas, New Mexico, Arizona, and the Nevada and California borders with Arizona. The other three species are truly southwestern bats; they have very restricted distributions in the United States and are found only in parts of California, Nevada, Arizona, and New Mexico. In a U.S. Fish and Wildlife Service survey, bat expert Don Wilson found that Sanborn's long-nosed bat a species critically important in the pollination of many agaves and giant cacti in southwestern deserts has disappeared from most of its former roost sites, now occupying only one known roost in the United States [BATS, December 1987, Summer 1988].
In the 1950's, Sanborn's long-nosed bats, Townsend's big-eared bats, and the Cave myotis all used Colossal Cave as a maternity roost. Sanborn's long-nosed bats were the most numerous. In 1956, Cockrum counted 1,000 juveniles hanging in a cluster in the "maternity room." Some sources have given figures as high as 20,000 bats once utilizing the cave.
Today, however, there are no bats in Colossal Cave.
And until I inquired three months ago, bats were not even mentioned during the guided tours! This is sad, because many visitors would have marveled that the geological feature had once held such a biological treasure. I would have felt cheated.
Visitors are guided through the largest chambers along a quarter-mile path built by the Civilian Conservation Corps during the Great Depression of the 1930's. The "bat cave"is separated from the visitor area by a pathway that requires minor spelunking. There are two other openings into the bat room from outside the cave. The primary one is a tunnel excavated before World War I for guano mining. There must have been large colonies regularly using the cave to warrant such an effort. Cockrum observed this to be the major access route used by the bats. The other opening is a tortuous passageway in the back which, according to local lore, was an escape route for bandits who hid their booty inside the cave.
In 1956, Joe Maierhauser took over the cave concession and has held it ever since. In many respects, his management has been good for the cave. He stopped vandalism, maintained the surrounding park grounds, and he has put his heart into the endeavor. But some of his well-intended changes have had tragic consequences for the bats.
To stop vandalism, he sealed the 'bandit exit' with concrete. And to rid the cave of the smell of guano, he placed a huge exhaust fan in the mine tunnel to draw out the guano-enriched air. The fan and duct work now completely block the bats' preferred access route. According to field notes and records at the University of Arizona Mammal Museum (where Cockrum is Curator), four of the previously listed bat species were easily netted in the cave in early June of 1966. Later that month the fan was put in, and within a year only two bats were netted in the entire cave.
Maierhauser is quick to point out to the Parks and Recreation Department that the bats are welcome and still have access through the main tourist entrance. However, this was probably never a natural route for them, and they are even more unlikely to use it because of the human traffic. Environmental impact statements to evaluate situations such as this before action is taken are a necessity now, but were not required in 1966 when the fan was put in.
Bat biologists have found that Leptonycteris is a species easily disturbed by human activity, fleeing quickly from contact. But probably more damaging to the Colossal Cave bats was the change in climate within the maternity room, caused by outside air being forced through it. This was the nursery area where mothers entrusted their young to warm temperatures and appropriate humidity when they left to drink nectar from nearby cactus flowers. With the night's cool air being blown across their babies, was it any wonder that the bats left?
I discovered these modifications to the cave in 1985 when I was asked to locate some nectar-feeding bats for a PBS nature production on saguaro cactus. We found just two Cave myotis in the entire cave. A few weeks later Colossal Cave was checked off the U.S. Fish and Wildlife Service survey list of previous Leptonycteris roosts. I assumed the cave was privately owned and didn't give much more attention to the matter. Then in March of 1988, I learned that the cave was state property and therefore public land. We Arizonans take great pride in our public lands. We cherish the freedom, the land and its inhabitants. I now wanted to protect the bats on our public land.
I accompanied Pima County Supervisor David Yetman and local Sierra Club conservation chairman Dale Turner to the cave to speak with Joe Maierhauser. Explaining the biological reasons and the ecological implications, I proposed that the mine tunnel and rear exits be reopened to allow bat access once again. Maierhauser expressed hesitation about returning the cave to earlier conditions. His reasons varied.
He feared that the County Health and State Land departments might require him to destroy the bats for public safety. Fortunately, we've come a long way in 20 years. The State Land Department commented that their policy is to protect wildlife (including bats) on public lands. The Country Health Department said they do not perceive the bats to be a public health threat in this natural situation.
Maierhauser then noted that his insurance rates could skyrocket because of the hazards that the public perceives are posed by bats. Visitors could be frightened, might trip and fall, and lawsuits could be expensive. I have tried to counter these ideas by telling him that many people are interested in bats, want to know about them, and would love to learn about their role in the local ecosystem. Thousands of tourists each year attest to this fact when they visit Carlsbad Caverns National Park and pass right by the bat portion of that cave on the tour route, often staying to see the bat flight program afterward. I suggested he include current information about bats and especially their history in the cave to entice interested visitors. I mentioned the possibility of selling bat-related items such as those which are sold at Carlsbad and through BCI.
A compromise was offered by Maierhauser. He reopened the rear 'bandit exit' which leads into a chamber not historically used by bats. He says they are welcome there. Unfortunately, as many bat enthusiasts waiting for bats to take up residence at their home will testify, offering a site to bats does not a roost make. Only special sites meet the critical criteria defining a roost, and the availability of these sites has been shown to be a potential limiting factor to the distribution and abundance of bats, especially Leptonycteris.
The Pima County Parks and Recreation Commission is now carefully evaluating the options for Colossal Cave and has been consulting with Bat Conservation International and other groups. The outcome is now in their hands and they will soon decide whether to return the original maternity roost to the bats. The future of southwestern deserts may hinge on their action.
Ronnie Sidner is working toward a Ph.D. in biology at the University of Arizona. She is an active BCI member, lecturing about bats throughout the state and presenting BCI's slide program.
NOTE: Both species of long-nosed bats, Leptonycteris sanborni and L. nivalis, are soon expected to be added to the U.S. Endangered Species List.
Above: A large nursery colony of Sanborn's long-nosed bats was forced to abandon Colossal Cave in Arizona, when it was opened for tourism. This one has its face covered with pollen from a visit to a cactus flower. PHOTO BY MERLIN D. TUTTLE
Saguaro National Monument is only a few miles from Colossal Cave, but the long-nosed bats that once made the cave their home are no longer there to pollinate the flowers of these giant cacti. PHOTO BY MERLIN D. TUTTLE