The University of Arizona

Education & Research Needed to Protect Tucson Bats, Scientists Say

By Kara Nyberg, August 6, 2002

Bats  commonly roost under bridges like this one, over a small wash in northeastern Tucson (Photo: Sandy Wolf)
Bats commonly roost under bridges like this one, over a small wash in northeastern Tucson (Photo: Sandy Wolf)
Bridge crevices make ideal bat maternity wards. Biologists enlist cooperation from Tucson transportation officials in protecting bat colonies that form here. (Photo: Sandy Wolf)
Bridge crevices make ideal bat maternity wards. Biologists enlist cooperation from Tucson transportation officials in protecting bat colonies that form here. (Photo: Sandy Wolf)
Mexican free-tailed bats - like the one here - roost by the thousands under Tucson bridges. The bats are a vital part of the Sonoran Desert ecosystem. (Photo: Sandy Wolf)
Mexican free-tailed bats - like the one here - roost by the thousands under Tucson bridges. The bats are a vital part of the Sonoran Desert ecosystem. (Photo: Sandy Wolf)
Pallid bats feature inch-long ears and light yellowish fur. (Photo: Sandy Wolf)
Pallid bats feature inch-long ears and light yellowish fur. (Photo: Sandy Wolf)
Mexican free-tailed bats form colonies numbering in the thousands around Tucson. (Photo: Sandy Wolf)
Mexican free-tailed bats form colonies numbering in the thousands around Tucson. (Photo: Sandy Wolf)

Bats are bountiful in Tucson. But they're at risk. Ongoing research and education efforts by the University of Arizona and Arizona Game and Fish Department aim to reduce the threat to bats.

"People have no idea how many bats are flying around here in Tucson, " says bat biologist Sandy Wolf.

Wolf has studied bats – some forming colonies numbering in the thousands – that reside under bridges, house eaves, and in caves around Tucson. These aren't the blood-sucking monsters sensationalized in movies or the rabid rodents that fly into people's hair. Rather, the eight bat species that seasonally inhabit Tucson prefer to feast on insects and agave nectar and shy away from human contact.

Bats pay a huge service to the environment in and around Tucson, Wolf says. Worldwide, bats eat tons of insect pests, which in turn saves farmers billions of dollars annually on pesticide and crop protection costs. Some small insect-eating bats can consume up to 2,000 mosquito-sized insects in one night. They also disperse seeds and pollinate many plants. The Sonoran Desert ecosystem relies on nectar-feeding bats as the main means of pollinating saguaro cacti, biologists have found. In addition, bat waste or guano is a rich fertilizer that can be mined from caves.

Despite all the good that bats do, fearful misconceptions of these gentle creatures persist because people just don't realize that bats are beneficial. And these misunderstandings may well lead to the demise of these animals, biologists fear.

Wolf says that the biggest local threat to bat populations is people who vandalize their roosts or needlessly kill bats out of ignorance or fear. Because bats live in huge colonies and reproduce slowly – most mothers give birth to only one pup a year – one single act of vandalism can destroy hundreds or thousands of bats, leaving them vulnerable to extinction. Bat Conservation International reports that more than 50 percent of American bat species are in severe decline or already appear on endangered species lists.

Education is the most important strategy when it comes to protecting local bat populations from human threats says William Shaw, a UA professor in the School of Renewable Resources. "Most people are simply unaware that these interesting and beneficial animals can and do live in close association with humans, " he says.

Tucson residents are most likely to encounter one of three species living under their roof eaves or nearby bridges. Two species prefer to make their homes in the shelter of deep crevices under bridges. These include Mexican free-tailed bats that live here year-round in huge colonies and the tiny, solitary western pipistrelle. A third species, big browns, fancy house eaves and live in Tucson primarily during the warm season. Another major Tucson bat species, the cave myotis, favor the seclusion of caves and mines on the outskirts of town.

To help protect bats, organizations like the Arizona Game and Fish Department strive to educate the public about these creatures. Scott Richardson, an Arizona Game and Fish employee, explains that the department tries to reach all sectors of the community when it comes to bat education. Employees regularly speak to community groups and construction workers regarding the impact they may have on bats. Moreover, Richardson finds that kids love learning about bats. He credits the local Tucson schools for welcoming Game and Fish workers to teach students about bats and for designing class units on bat education.

Wolf is funded by Arizona Fish and Game to further the education effort. She gives talks on the benefits of bats to classes from elementary school to the college level. Previously a music teacher, Wolf moved to Tucson in 1993 to study wildlife ecology and found bat biology to be her passion.

She says, "People can be pro-wildlife by donating money to funds, such as for grizzlies or wolf relocation. But when it comes to wildlife on their doorstep, that's the real test for people."

Richardson agrees. Some Tucson homeowners with bat occupants regard the creatures as an annoyance. Bats leave droppings, streak walls with urine, and make lots of noise with their persistent squeaking. Tucson homeowners often resort to pest control companies to get rid of bats. However, pest control professionals cannot legally kill bats. Not to worry, Game and Fish makes house calls to bat-infested residences to promote human and bat cohabitation. Freestanding bat boxes - like mini condominiums for bats - can be placed in backyards as a popular alternative for bats that otherwise might live in attics or under house eaves.

As for protecting the bats that roost under bridges, Wolf does what she can. Funded by the Arizona Game and Fish Heritage Fund, she conducted a year-long research project studying bats under Tucson bridges as part of her master's thesis in zoology from the University of Arizona.

Beginning in January of 1999, Wolf monthly monitored 43 bridges throughout the city in an attempt to determine why a particular bat species prefers one bridge to another. Her survey found that bats roosted under 35 of the 43 Tucson bridges. Wolf discovered that the largest colony consisted of at least 11,000 Mexican free-tailed bats, amazingly. Because these bats can line bridge crevices layered on top of one another, Wolf predicts her estimate may be low, that this particular colony may have as many as 20,000 members.

Wolf's studies also included detailed information about the bridges and surrounding environment. For example, she measured the width and depth of all vertical crevices under the bridges, the height of the bridges, land use and development around the bridges, surrounding vegetation, local human activity, and features under the bridges, such as a wash or a street. Collecting such information wasn't easy. Wolf injured her shoulder because of repetitive motion from all the measuring.

Because no one has previously conducted a bat survey of this magnitude within Tucson, the data that Wolf collected may prove invaluable. Game and Fish plans to use the information to work with the city transportation department to schedule bridge construction work at times of least disturbance to the bats. In addition, because the current design of bridges has changed, Game and Fish also seeks to work with the city to retrofit new bridges with structures that will provide roost space and promote bat colonization.

Game and Fish officials can only speculate on what impact humans have on bats because bats have been monitored intensively only for the past six to seven years.

UA Professor Shaw notes, though, that "many insect-eating species have suffered from the use of agricultural pesticides, and nectar-feeding species suffer when native plant species are impacted by human land uses." This is in addition to all the bats affected by vandalism or unwitting roost disruption.

UA and Arizona Game and Fish researchers plan ongoing efforts to protect Tucson's bat communities.