​​​​​Suggested Acoustic Search Areas for North American Bat Species by NABat Grid Cell  a Product of the NABat Stationary Acoustic Working Group

​

​

​

 

Summary: The NABat Stationary Acoustic Working Group is comprised of members with diverse geographic and species-specific expertise related to stationary acoustic surveys for bats. The working group collaborated with state, provincial, and regional bat experts to develop suggested search areas for North American bat species. These search areas are geographies where a specified bat species may occur and therefore should be considered for inclusion in the list of candidate species when analyzing echolocation recordings and assigning a species ID. The primary purpose of this effort is to produce candidate species lists for each NABat grid cell that can be considered when undertaking acoustic analyses (i.e., using autoID software to classify bat recordings to species). It is expected that acoustic search areas will require updating through time to account for changes in populations and incorporating new or updated information sources.  

​

Background and Need: The list of bat species selected for consideration by the autoclassification software and by manual vetters is important for ensuring accurate acoustic processing results for a given geography where recordings were collected. When using acoustic classification software to process bat call data, the list of species considered by a software’s classifier impacts how the calls are parameterized and classified to species. This can potentially lead to mis- or missed classifications if the species included in the classifier are not appropriate for the geography of interest.  

Species range maps can help inform the list of bat species selected for consideration when auto-classifying and manually vetting acoustic recordings, however, because some known or suspected changes in species distributions (e.g., Brazilian free-tailed bat, evening bat) are not reflected in these maps, and because true species ranges cannot be fully known, these range maps are not sufficient on their own. Currently there are four primary sources for North American Bat species ranges -- U.S. Fish and Wildlife Service Environmental Conservation Online System (ECOS), National Atlas, NatureServe, and International Union for the Conservation of Nature (IUCN) (Table 1). The species ranges provided by these sources can sometimes be in conflict and therefore serve as a source of confusion for analysts determining which species should be considered during acoustic data processing. Moreover, it is important to distinguish between polygons intended to depict species ranges (i.e., where species are expected to occur based on historical records, contemporary observation data, or expert elicitation) and species acoustic search area polygons (i.e., where it is reasonable to look for a species based on the understanding that species range boundaries can change through time). The latter support acoustic surveys that can be used to document changes in species distributions. 

Commercial and open-source software available for auto-classifying and manually vetting acoustic recordings of bat echolocation measures often provide users a default list of species for the software to consider for a given geography. If a species is missing from the list of considered species, it will not be considered for classification and, thus, cannot be detected. A single list of species to consider during acoustic survey analyses at the scale of a 10-km x 10-km NABat grid cell will help guide acoustic data processers in species list selection, particularly biologists/data processors not experienced with the details of the local bat fauna.  

 

Goal: To provide users a default list of species to include for consideration during processing of bat acoustic files. In particular, this list will help users select which species to include when using automated identification software. Examples include, customizing species lists and comparing regional or subregional classifiers to the list of species that should be considered for a given NABat grid cell.   

 

The desired outcome is a single species list that accounts for species expected to occur within a NABat grid cell, as well as species that may occur within the cell (i.e., rare species, just outside existing species ranges, species with putative range expansions). Working group members sought a balance between a species list that was liberal (i.e., considered all the species that may occur in an area) yet did not include species that were unlikely to occur, which would lower confidence of automated identification software and suggest false positives for species identifications.  

 

Primary Audience: Users that are biologists but not experienced with the details of the local bat fauna.  Examples include professional agency biologists that survey for a wide variety of taxa and participate in the NABat program intermittently within a given year, or bat biologists conducting surveys in a new locality for which they do not have a detailed understanding of the bat fauna.  

Users experienced with the local bat fauna likely already have a default list of species that should be considered in acoustic surveys. Such users are invited to reference these resources for consideration or to provide suggested updates such that their expertise may be represented in future iterations.  

Intended Product: A list accessible via the NABat Partner Portal that documents the suggested species to consider by grid cell (i.e., include in the species list) during acoustic survey analyses carried out for geographies of interest (e.g., cells selected for survey in a project). 

 

This product does not represent and should not be interpreted as altered or adjusted range maps.  

Versioning: We expect that species ranges will change over time and that we will learn more about contemporary distributions of individual species via the NABat program and other efforts. As such, the list of species to be considered in each cell should be updated over time. Working group members propose this should occur every 5 years and should be a task coordinated by the NABat Stationary Acoustic Working Group unless a quantitative procedure has been developed that would generate species lists based on data.  

 

Process: Working group members and state/provincial level points of contact (POC) reviewed existing, publicly available range maps and considered where edits to these polygons may be warranted to produce reasonable search area for each species. As part of this process, participants considered the possibility of expansion, contraction, or shifting ranges and provided input on search area polygons that would enable observation of any such changes to species occurrence and range boundaries. Individual input was based on training, education, and expertise of participants and their familiarity with known data records. Resulting species-specific feedback was based on local knowledge for a given species and potential rates and regions of range expansion. Participants refrained from providing input on species or geographies where they did not possess local knowledge. As a result, buffers were not extended into states or provinces where the search area polygon would intrude into a new state or province for a given species without state/provincial concurrence.

 

Specific steps included:  

• Generating digitally editable polygons that merged existing range map sources (Table 1 below).​​​​​​​​​​​

• ​​​​​Digitally editable polygons of merged range maps by species were made available to Stationary Acoustic Working Group members and observers who were able to edit polygons to reflect their input on where specific species should be looked for based on their expertise.  

• Digitally editable polygons of merged range maps by species were also distributed to state/provincial level points of contact (POC) for bats and their feedback invited on the proposed search area polygons. State/provincial POCs had the option to provide input directly and/or seek additional input from other local experts.  

• Input from working group participants and POCs were compiled and integrated to create acoustic search area polygons for each species.  

• Smoothed and simplified acoustic search area polygons were generated by species with additional 10-km terrestrial boundary buffers and off-shore buffers of 150-km when a species terrestrial range extended to the edge of the continent. Where range boundaries occurred along the Great Lakes, the search area boundaries were extended to the midpoint of the lake or were connected directly if the search area continued on the other side of the lake. 

• Maps of the final species-specific Acoustic Search Areas (2025) are stored with the NABat Stationary Acoustic Working Group as an archive. 

• Acoustic search area polygons were joined to each NABat grid frame to produce a default species list for each 10-km x 10-km grid cell.  

​

These default species lists by grid cell may be adopted for use in commercial and open-source software, on the NABat Partner Portal, and additional use cases not explicitly defined here.  

 

 

Table 1. ​​​​