Cofrin Center for Biodiversity

bat station

The Acoustic Recording Equipment

A bat monitoring station has been installed in the Cofrin Arboretum near the bay shore. The bat recording station at the Arboretum Bay shore was provided and installed by the WI DNR. This station will provide us with a continuous record of what bats species are active in the area near the station.

The station consists of the recording equipment and a solar panel that powers the entire unit. The ultrasonic echolocation calls made by the bats are collected by the detector and then converted to audible output that we can hear but are of frequencies directly related to those being made by the bats. The data is then stored as digital files The files can later be downloaded to a computer and viewed using specialized software that allows scientists to match calls to bat species and sometimes allow the measurement of different behavioral activities, such as foraging for food.

Why the bay shore?

UWGB undergraduate Courtney Lewis received a Cofrin Research Grant to determine the best area on the arboretum to locate the station. She used an ANABAT mobile recording unit to locate bats and found that the highest levels of bat activity was along the campus bay shore. You can read more about her project here.

Seeing With Ears

Traditional methods to study bat diversity and ecology usually involve the use of mist nets to trap bats that are then identified and released. This is often difficult work because it has to be done at night and requires special training so that the bats are not harmed. Even when done properly it is time consuming and causes unnecessary stress for the bats. Using special equipment to record the high frequency echolocation calls used by some bats allows scientists to easily collect data on the presence of bats species without interfering with the bat’s behavior.

All of the bats that occur in northeastern Wisconsin are in a group of bats called the Microchiroptera. One of the distinctive features of this group is that they all use echolocation to navigate as they fly. A bat emits a high frequency sound that if it hits a solid object bounces back as an echo. This system provides the bat with such detailed information that it can locate even tiny insects. Each species of bat has a recognizable signal signature allowing scientists to identify species that are active around the recorder.

These sounds are different than the vocalizations that the bats use to communicate with each other and that we hear as squeaks or chirps. Echolocation is much higher pitched and inaudible to the human ear. Different species use different pitches for echolocation sounds but all range from 20-200 kilohertz (kHz). There are two main types of frequency patterns used by bat species. Bats can use a constant frequency (CF) pattern, which never changes in pitch or they can use a frequency modulated (FM) pattern where the call starts at one pitch and descends over the length of the call to a lower pitch. Most bats use a combination of patterns to determine the precise location of an object. CF patterns detect that an object is present, but the FM pattern provides a detailed outline of the object in space, how far away it is, and if the object is moving its velocity. Every bat species uses a unique combination of patterns and pitches that allows scientists to match echolocation recordings to a single species.

The distance at which the acoustic recording equipment and the bats themselves can detect echolocation sounds is a relatively small area because the air quickly dampens sound of shorter wavelengths. Most bats can only locate objects up to about 15 meters (50 feet) away. Some bats increase their range by producing high intensity (up to 120 decibel) sounds that of course we cannot hear, but should deafen the bats that make them. These species, including our own Little Brown Bat (Myotis lucifugus) and the Big Brown Bat (Eptesicus fuscus) are able to momentarily deafen themselves by contracting muscles in their inner ears as they call that prevent the bones of this delicate organ from being damaged. The middle ear muscles relax, restoring the bat's hearing so it can receive echo signals bouncing off the objects around it.

Reading the Signals

Once the data is downloaded, a software program translates the signals into a sound that can be heard and graphed by researchers. Each bat has a particular signature that can be used to identify it. There are also lots of other sounds that are picked up by the recorder including insects and even the waves from Lake Michigan that must be separated from the bat data.

Bat Species in the Cofrin Arboretum

So far the bat recorder has identified the presence of XXX species of bats on the Arboretum bay shore. These species include XXXX,XXXX…..

Species Descriptions

Little brown bat (Myotis lucifugus) This species is a medium sized bat that has an olive to brown fur with large ears. This bat is active at all times of the night, but feeding reaches its peak a couple hours after sunset. When this species enters its state of rest during the day, it can be found in hollowed trees, underneath loose bark, or any dark, undisturbed areas.This bat mainly feeds on insects such as mayflies and chironomids.

Biodiversity Topics: Introduction . Plants . Animals . Mammals . Birds . Reptiles & Amphibians . Arthropods . Spiders . Insects