Bats are mammals of the Order Chiroptera, or “hand wing”, as their forelimbs have been adapted into wings (2). Due to this adaptation, they are the only mammal capable of true and sustained flight (2). They are the second largest order of mammals with over 1400 species (2).

Bats are found all over the world except in Antarctica. The majority of bats in the Midwest US are classified as microbats (Microchiroptera). The microbats utilize echolocation and are mainly insectivores; however, some feed on fruit, nectar, pollen, fish, frogs, small mammals, or blood. The external ears of microbats do not close to form a ring with the edges separated from each other at the base of the ear (17). Their cousins, the megabats (Megachiroptera), are mainly frugivores (fruit-eaters) or nectarivores (nectar-eaters). The megabats mainly live in tropical regions and do not utilize echolocation. Megabats have a well-developed eyesight and a claw on the second finger of the forelimb (17).

According to Jack Stenger, Conservation Biologist at Great Parks of Hamilton County, in the Midwestern USA, there are 12 species of bats which are typically found in caves, rock crevices, old buildings, bridges, mines and trees. There are a few species of bats that will migrate south during the winter, but most species will stay in the same area and hibernate.

The various species of Midwestern US bats have wingspans between 5-15 inches long and weigh between 5-30 grams.

Bats only have one pup per year which makes them extremely vulnerable to extinction (2).

Globally, there are 21 bat species critically endangered and face imminent risk of becoming extinct, 83 bat species endangered, 109 bat species considered vulnerable and 242 bat species considered "data deficient", which is an indicator that more conservation attention is needed for these species (2).

There are currently declines in the bat populations due to habitat loss and fragmentation, White-Nose Syndrome, insect population declines, wind energy development, climate change, and human disturbance. White-Nose Syndrome is caused by a fungal pathogen called Pseudogymnoascus destructans. It causes them to wake more frequently during hibernation due to increased body temperature as the bat is fighting the fungus. White-Nose Syndrome, along with human disturbances during hibernation, cause the bats to wake frequently, depletes their energy stores, and leads to their death. Wind energy development is detrimental to the migrating bat populations as the bats run into the wind turbines as they are migrating and die. Insect population declines lead to a smaller food source for bats. In addition, habitat loss and fragmentation and climate change leads to less areas for bats to roost, raise young, and find food (16).

Due to several Midwestern US species of bats becoming endangered and entering the IUCN Red List, such as the Northern Long-eared Bat (Myotis septentrionalis), Indiana Bat (Myotis sodalis), Little Brown Bat (Myotis lucifugus) and Tri-Colored Bat (Pipistrellus subflavus), many conservation groups are trying to stop the declines in population through conservation efforts (9). Those efforts include gating entrances to caves and mines, building bat houses, educating the public, research, and saving and restoring forest ecosystems (2).

The standard protocol for recording bat echolocation calls typically involves recording from sunset to sunrise (5). The high frequency microphones record bat echolocation (ultrasonic waves) and save the information onto a storage device. From there, the bat pass (series of calls) is transferred to a computer analysis software. The analysis software allows the researcher or scientist to see sound wave frequencies and hear the bat calls. Based on the unique features of each call, researchers are able to narrow down the bat species present (5). To help determine the species, there are several bat call libraries available online (4).

There are two types of acoustic monitors available and in use in the field, which are passive and portable (or active). These monitors are also known as stationary surveys and mobile transects, respectively. Passive acoustic monitors entail large microphones and a recording device attached to a pole which is placed in a field, riparian environment, or forest and left for long periods of time. Portable (active) acoustic monitors are small and handheld with microphones that can be attached to the outside of a car or carried around (3). Bat researchers or volunteers then drive slowly through areas with the monitors and collect data. Both forms have been found to be highly successful in obtaining information on bats.

Heterodyne detectors-detect narrow range of frequencies and convert sounds of those frequencies to audible (to humans) sounds in real time. This provides a quick method to listen for bat presence (1, 4).

Broadband detectors-detect a range of frequencies simultaneously, to identify species, especially in communities where calls vary in frequency (1, 4).

There are many questions that need to be answered when determining the type of detector that you want to use in the field. For more information on the questions that you should be asking prior to buying a detector, please refer to https://www.batcon.org/wp-content/uploads/2020/09/Bat_Echolocation_Research_2nd_Ed_20200918.pdf.

Microphone sensitivity is equally important as the detector. Bats using low-intensity echolocation calls dominated by higher frequencies are harder to detect than those using high-intensity calls dominated by lower frequencies. Thus, researchers must be aware of the bat community that they are studying prior to selecting an acoustic monitoring device (1, 4).

Some acoustic monitoring system examples include (1):

1) Anabat detecting and recording system by Titley electronics (www.titley.com.au)

2) AR125 detector and FR125 eld recorder by Binary Acoustic Technology (BAT; www.binaryacoustictech.com)

3) Song Meter SM2BAT+ detector/recorder by Wildlife Acoustics (www.wildlifeacoustics.com)