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Besides using appropriate sampling techniques for each species, controlling for or at least recording the natural, environmental and temporal conditions that affect bat activity will help compare data across habitats and monitoring sessions.
Some things to take into consideration are:
Local weather conditions
Natural and artificial light
The following data were returned:
16 species were captured in nets and/or traps
14 species were captured acoustically (both passive and active)
5 species were only captured in nets and/or traps
2 species were only captured with passive acoustic detection
3 species were only captured with active acoustic detection
A total of 21 species were “captured” at the site.
In 18-years of long-term monitoring at this site, the total number of species physically captured was: 20.
In one night we were able to obtain records of more species than was possible during nearly 20-years of physical captures, simply by adding acoustic captures to the effort.
At our AZ workshop location in 2009, mist nets and harp traps were deployed along with passive TE and active FD bat detectors during a single evening of monitoring. During the survey, we deployed 10 net/trap sites including 4 single-high 18-foot nets, 3 single-high 30-foot nets, 1 single-high 42-foot net, two large harp traps, and one 3H 18-foot net and one 3H 42-foot net. This accounted for 48 total net/trap-hours.
We also deployed 2 Pettersson D240x HET/TE bat detectors, connected to iRiver MP3 recorders in a passive configuration in between our two most separate net/trap sites. This accounted for a total of 8 passive detector-hours.
We also had two staff outfitted with AnaBat SD2 + AnaPocket bat detectors and spotlights deployed in a large clearing across the road from our creek-side net-trap and passive detector sites. This accounted for a total of 6 active detector-hours
A total of 12 personnel were deployed manning detectors and nets/traps for a total of 72 net/trap/detector-hours.
Select appropriate net/trap sites . . . Net along flyways, at water resources and trap constrictions like cave entrances or narrow flight paths between resources.
Deploy 1-2 passive acoustic recorders in the habitat being sampled with nets and traps. Acoustic stations should be near but not adjacent to the net/trap sites so movement between net/traps and processing stations don’t add ultrasound noise to the recording event OR scare bats away from the recording station.
Select 1-2 people to perform an acoustic transect through the sampling location. This can be a passive collection done in compliance with the Britzke Protocol or which ever protocol your state suggests.
Select 1-2 people to man an “active acoustic monitoring” station using bat detectors, real-time signal analysis (e.g., AnaBat) software, spotlight and trained observers.
Active monitoring with bat detectors can also be used to sample in between mist-net checks. In areas where the majority of the species use high-intensity echolocation calls, simultaneous sampling with FD or TE detectors and signal analysis software can detect the presence of more species than mist nets.
Yet, the most complete picture of bat communities can be discovered when bat detectors are used passively in conjunction with mist nets. Using a variety of “capture” methods maximizes the probability of detecting all species in an area.
Adding Acoustics to
Capture Survey Methods