Mobile Acoustic Monitoring
Mobile acoustic monitoring is a common type of bat monitoring data in the NABat program, and many partners of the Midwest Bat Hub have used this type of bat monitoring in the past. NABat proposes specific data collection protocols for mobile acoustic monitoring, as explained at length in Loeb et al. (2015) – pages 29-34. Here, this protocol is summarized.
- Detector types: Time expansion recorders cannot be used.
- Microphones: Omnidirectional microphones are not recommended.
- Variability among detectors: Minimizing variability among detectors is especially important during mobile transects as the data is used to estimate relative abundance. Continued calibrating the detectors is therefore recommended.
- Route selection: Mobile bat monitoring is conducted by driving specified transects. These transects should be safe to drive at 20mi/hr with minimal stopping. Do not use rough roads. Use hazard lights warning others of your low speed.
- Road types: Two-lane secondary or tertiary roads with few if any stops.
- Route length: Approx. 15 to 30 mi in length and fit primarily in a grid cell. The route should not cross back into itself.
- Habitat type: Areas with dense forested corridors and a low canopy should be avoided.
- Timing: Twice during the maternity season. Both surveys should be conducted within a week. In subsequent years, surveys should be conducted within 1 to 2 weeks of the original survey. Surveys should begin 45 minutes after sunset.
Stationary Acoustic Monitoring
Perhaps the most common type of bat monitoring data in the NABat database is collected from stationary bat detectors. These detector stations are designed to operate many nights over a long time, but they can of course only monitor in one specific place. The proposed NABat protocol for this type of monitoring is specified in Loeb et al. (2015) – pages 20-38. The protocol is summarized here:
- Detector type: The use of time expansion detectors is not recommended.
- Microphone: Both omnidirectional and directional microphones can be used but should be used consistently.
- Recording settings: It is recommended that a 2-second trigger window and a maximum file length of 15 seconds be used.
- Number of detectors: Two to four detectors in a cell, in different 5x5km quadrants. Detectors should be placed in areas that maximize the number and quality of recordings.
- Site consistency: The same sites should be used across years. It is therefore critical that good sites are selected.
- Habitat location: It is desirable to monitor bats in a variety of habitats. For heterogeneous landscapes, place up to four detectors such that they sample different habitat features, preferably one within each quadrant of the cell.
- Equipment setup: Directional microphones should be at least 5 ft above ground, and omnidirectional microphones should be placed even higher to reduce background noise and echoes from the ground.
- Timing: Surveys should be conducted during the summer active period prior to the young becoming volant. Detectors should run the entire night, from 15 minutes prior to sunset to 15 minutes after sunrise, for a minimum of four nights.