Using Acoustic Surveys to Monitor Population Trends in Bats

Bat populations are potentially being impacted by 2 relatively recent sources of mortality: White Nose Syndrome (WNS) and wind energy development. While it is often easy for us to document the mortality of these 2 factors at a particular site, the impact of these sources of mortality on bat populations is currently unknown. In the case of wind turbine mortality, we can estimate the number of bats killed but we have, at best, a poor idea of population size and the ability of these populations to sustain this rate of mortality. Therefore, in addition to hibernacula surveys and post construction mortality surveys at wind-power sites, we need a supporting method to assess the impacts to multiple species on a broad geographic scale.

Several techniques can provide useful data on bats during the maternity season. Exit counts at maternity roosts can provide information on local level and assessment of reproductive conditions of bats can determine the impacts on reproductive rate. However, these techniques are focused on sites that can be effectively counted or on species that can be captured at roost sites.

Recording of echolocation calls of bats as the researcher moves along a transect has been commonly used in Europe to monitor bat populations. Ultrasonic detectors are a cost effective method for monitoring multiple bat species at large spatial scales. Therefore, we initiate a project in 2009 to establish a bat monitoring program using acoustic surveys along transects.

Transect Development Guidelines
These are simply guidelines for the creation of the transects. By following these guidelines, researchers maximize the comparability of their results with other, but the analysis is setup to allow transect to be molded to meet site specific requirements.

1. The transect
   1. should be ~ 30 miles long along a path that minimizes sampling the same stretches of road (1 way straight line movement).
   2. should be safe to drive the transect at 20 mph
   3. should pass through common habitat types of the area
   4. should be easily sampled in successive years
   5. These are simply guidelines. If you cannot come up with a transect that is 30 miles long then use a shorter version.
2. Sampling
   1. Any type of bat detector that allows for recording of echolocation calls can be used (except time expansion systems). The important thing is that the same type of detector is used whenever a transect is sampled.
   2. Sampling should be done during the time when bats are on their maternity range. To exclude most of the migrants, the period of June 1 to July 15 is probably a pretty good guide. Note: However this technique can also be applied to survey for bats outside the maternity areas, so sampling anytime bats are active in your area is beneficial.
   3. Monitoring should only be conducted on nights that are suitable for bat activity (low wind, no rain/fog, suitable temperatures for bat activity)
   4. The bat detector should be placed on the roof of the vehicle pointed straight up. While people have flexibility to use whatever setups they want for deployment, here is a set of instructions for a setup using the Binary system and here is a picture showing a setup of an Anabat system.
   5. Sampling should be initiated 30 minuets after sunset
   6. The transect should be sampled a minimum of 1 – 3 times throughout the summer. If you are going to sample a site multiple times then it is best to spread out sampling throughout the maternity season
   7. If possible, it is advisable to use a computer attached to a GPS unit to mark the location when the recording is being conducted. Alternatively, you can mark the transect with a GPS when you are not sampling. Each transect should be marked with a GPS point for the start and end points and an associated map with the route marked.
   8. Sensitivity of the detector should be ~ 7 for Anabat. If possible it is always a good idea to calibrate the equipment to make sure that it is functioning properly.

For all sampling done please fill out a datasheet that provides basic information on the transect.

A webinar we recorded on 9 December 2009.

• PowerPoint Presentation
• Video of Presentation

  Questions and/or data can be sent to:
  Eric Britzke
  US Army Engineer Research and Development Center
  EE-E/ Building 1006
  3909 Halls Ferry Road
  Vicksburg, MS 39180
  Phone (601) 634-3641
  Email: Eric.R.Britzke@usace.army.mil