Arboretum bat monitoring station provides valuable information


Very little information exists about bats in Wisconsin: Where are the different bat species in the state? Are they resident or migrating through the area? When are they active? Those are a few of the questions Wisconsin DNR Bat Ecologist David Redell hopes to answer.

With that goal in mind, Redell installed a bat monitoring station at the Arboretum on the edge of Curtis Prairie early in the summer of 2007. The station detects and records acoustic signals as bats fly by and records the date and time of each bat pass.

“All bats in Wisconsin utilize echolocation to orient and navigate the dark night sky as well as detect, pursue, and capture insect prey as they fly through varying levels of clutter (tree limbs, etc.),” Redell explains.

“Because these bats echolocate in the ultrasound range (sound above the range of human hearing), we use an acoustic recording system capable of detecting these calls as the bats fly through the area.”

With this system, information is stored digitally on a compact flash card and downloaded once a month. Using software specifically designed for viewing the data, Redell can separate out the noise (insects, high levels of wind and rain) from the bats’ calls.

Once the files are cleaned to contain only bat calls, his team can begin analyzing the data for bat activity patterns. Each species of bat utilizes different frequency ranges of sound for their echolocation.

“By looking at these frequencies and shapes of the calls (viewing the sonograms), we can start separating out each species based on these sound characteristics,” says Redell.

“While there is occasionally some overlap in characteristics between some of the species, making visual identification difficult, we are currently working on building a reference library of echolocation calls (by capturing and identifying the bat in hand then releasing and recording the calls of each species) to create a statistically based identification model to further separate out the difficult groups.”

“With each bat passing the detector we get the date and time of the encounter,” says Redell. “Thus, we can begin describing seasonal and nightly timing of activity, phenology, migration, species occurrences and the relationship of bat activity with weather patterns.”

There are four other bat monitoring stations in addition to the one at the Arboretum. They are at the UW-Green Bay Cofrin Arboretum, the Urban Ecology Center in Milwaukee, the UW-Stevens Point Schmeekle Reserve and the UW-Madison’s Kemp Natural Resources Station in Woodruff.

“We had the funds available to deploy five long-term stations and wanted to get good site representation throughout the state,” says Redell. “We were also looking for areas that had individuals on-site who could download and transfer the data, and areas that were not subject to shifting land-use.”

According to Redell, the Arboretum provides a great study location in the southeast glacial plains. Redell’s team investigated a variety of possible locations at the Arboretum for placement of the monitoring station, considering habitat context, site access, prairie burn schedules and sun exposure for the solar panel.

Bats often fly along edge habitat and forest openings and are associated with water resources. The area near Margaret’s Council Ring (at the edge of Curtis Prairie) had the best context and possibility of detecting all species present at the site. Redell hopes to have operational equipment there for a minimum of 10 to 15 years.

To date, the Arboretum is the most diverse site according to Paul White, natural resource technician at the Wisconsin Department of Natural Resource’s Ecological Inventory and Monitoring unit. The species found here include little brown myotis, northern long-eared myotis, eastern red bat, eastern pipistrelle, hoary bat, big brown bat and possibly the silver-haired bat (during the fall migration).

“The silver-haired bat calls are very similar to that of the big brown bat, so until we gather more data we can not verify the silver-haired presence,” White reports.

Redell’s fascination with bats began in a terrestrial vertebrates class in his undergraduate days at UW-Madison’s Department of Wildlife Ecology. His professor, Scott Craven, planted the seed.

“That’s all it took for me to get hooked,” says Redell. “Here was a group of mammals that was understudied, had amazing sensory capabilities and natural history characteristics to maintain a lifetime of interest, and they became active at the same time as me—after dark. The more I learn about bats, the more interesting and amazing they become.”

Not everyone likes bats, Redell acknowledges. He points out that bats in Wisconsin are insectivorous in their foraging appetite. As primary predators of night-flying insects, bats consume a large number of insects, including forest and agricultural pests, as well as mosquitoes which carry and spread the West Nile Virus.

“Healthy populations of bats can reduce our reliance on pesticides and they provide these insect-eating services for free as long as they have adequate roosting areas, travel routes to foraging areas, and access to clean water,” Redell points out.

Redell is putting together a citizen-based bat monitoring program using equipment similar to that used at the Arboretum. However, instead of sampling a single location, citizens will be able to use hand-held bat detectors coupled with a GPS unit for conducting mobile surveys in their area.

The system will automatically record the route traveled along with the position and time of each bat encountered. From these data they will map distribution of species throughout the state and determine routes that may be used for monitoring on a yearly basis.

Those interested in getting involved and wanting to learn more about training or updates can contact Redell at or White at

Note: Parts of this article were adapted from a story that appeared in Kemp’s Point, the newsletter of the Kemp Natural Resources Station.

Located between Lake Wingra and the West Beltline Highway at 1207 Seminole Highway, the University of Wisconsin-Madison Arboretum features the restored prairies, forests and wetlands of pre-settlement Wisconsin. This 1,260-acre arboretum also houses flowering trees, shrubs and a world-famous lilac collection. Educational tours for groups and the general public, science and nature-based classes for all ages and abilities, and a wide variety of volunteer opportunities for groups, families and individuals are available.