Bats, Algorithms, and a Cemetery
What the Night Reveals
Carolyn Langlinais
Texas Nature Trackers The BAT Project: Standard Operating Procedure Preface:
In 2023, conversations began between the then Texas Parks and Wildlife Bat Specialist and Texas Nature Trackers (TNT) staff regarding the possibility of utilizing the skills of Texas Master Naturalist (TMN) volunteers across the state to assist with the collection of much-needed acoustic data on bats. In January 2024, after several months of securing equipment, a start-up private grant, and background work on how data is collected using acoustic monitors, a meeting was held on a #TMNTuesday through the state program to gauge the interest of each chapter. The meeting was attended and/or later watched by more than 500 TMNs.
After several more meetings and training, the equipment was shipped to participating chapters. The BAT Project was initiated on Monday, April 29, 2024, the first day of data collection, by 37 chapters.
Hays County Master Naturalists are participating in the North American Bat Monitoring Program (NABat) again this year. May 11 marked the start of another season of bat acoustic monitoring. For nine weeks during the summer, acoustic monitors are placed on properties throughout Hays County. Last year, we deployed only one monitor each week, and decisions about where to deploy it were largely left to the monitoring coordinator. This year, we have two monitors, and the criteria for selecting monitoring locations have become more stringent.
How do we decide where to deploy them? I'm glad you asked.
According to a U.S. Geological Survey data release published on October 22, 2018, NABat uses a grid-based sampling framework that spans Canada, the United States, and Mexico. The system divides the landscape into standardized grid cells and uses a Generalized Random-Tessellation Stratified (GRTS) survey design to create a randomized, spatially balanced sampling network. This approach helps ensure that monitoring efforts are scientifically rigorous while accounting for the wide-ranging movements of bats.
The Hays County GRTS map shows the highest-priority grid cells in the darkest red and with the lowest GRTS numbers. Each GRTS cell is divided into four quadrants: northeast, northwest, southeast, and southwest. Finding two sites to monitor within a GRTS cell each week has been a bit of a challenge, especially given the additional requirements that each monitor be placed in a different quadrant and more than 5 km from any other monitoring site.
From the map, you can see that the two Wimberley sites are too close to each other and are located in the same quadrant. An additional site will need to be found and monitored to correct this.
The area that has been most difficult for me to find sites in is along the Blanco-Hays county line, the triangular space with two sites that appear to sit directly on the border. One site for which I've obtained permission to survey is Henly Cemetery. Unfortunately, the only other site I've found in this GRTS cell is less than 5 km from the cemetery.
Finding a location involves working with the GRTS map, which allows me to zoom in but shows only roads, not business names, parks, or other landmarks. So I keep a Google map open on another screen and work between the two to narrow down potential locations. I found the cemetery by looking at a VRBO map and contacting the property owner. She initially thought I wanted to book her house for the week's monitoring! She was kind enough to put me in touch with her mother-in-law, whose home was too close to a previously monitored site, but who serves on the Henly Cemetery board. Bats in a cemetery, and it isn’t even Halloween!
The Technology
The monitors we use are Wild Acoustics SM4s.
Each monitor is affixed to an 8-foot-tall PVC pole, with the microphone zip-tied to the top. The monitor itself is attached about halfway down the pole. The wire between the two components is also zip-tied to the pole so that wind striking the cord does not create excess noise.
The monitors are deployed on Monday and retrieved on Friday, depending on site availability. We do have some wiggle room, but the requirement is to record for four consecutive nights. In most cases, we are able to attach the monitor to a fence post or tree.
Before deployment, the monitors are programmed with each site's longitude and latitude in decimal degrees. Programming the monitor with an exact GPS location allows it to calculate sunrise and sunset times. The monitor is then set to begin recording 30 minutes before sunset and stop recording 30 minutes after sunrise.
When placing the monitor, it's important to consider where bats may be flying. Bats drink on the wing, so placing the monitor where they pass on the way to a water source is a good strategy. Trees, bushes, and anything else that obscures the sky are considered clutter, so finding a location with a clutter-free view is also important.
This year, TPWD Texas Nature Tracker Coordinator Wendy Anderson created an ArcGIS Survey123 form that allows coordinators to collect data about site conditions using a phone app. Last year, all site specifications, site photos, required permission forms, and weather observations were completed manually, scanned, and emailed to TPWD. Now that information can be gathered in one place, stored as a draft until the monitor is retrieved, and submitted through the app.
During monitoring, sound files are saved to an SD card. When the monitor is retrieved, the files are downloaded to a computer. Wild Acoustics software, Kaleidoscope Pro (KPro), is then used to analyze the bat calls. The program's Auto-ID function assigns a level of identification certainty to each bat call.
Kaleidoscope Pro creates a spreadsheet in which each row represents a WAV file from the SD card. It also creates a spectrogram and an oscillogram, visual representations of the bat calls. In previous years, the bat analyzers would use a standard spectrogram of a bat species and make comparisons with each site’s bar spectrogram to determine which bats were heard. Now, the KPro software gives us a pulse count and match ratio so that the species can be identified without the analyzer, learning each bat species signature and making these comparisons.
The pulse count, together with the match ratio, determine whether a species identification is classifed as Highly Likely, Likely, Possible, or Needs More Data. The rubric for this determination is outline below.
Reporting a bat species required looking at the WAV file categories hierarchically. If a species had WAV files categorized as Likely, Possible, and Needs More Data, it would be recorded as Likely and reported as such to the landowner and NABat.
Last year, rather than comparing each line of the spreadsheet to the chart manually, I created an algorithm to do it for me. I also used conditional formatting to assign colors to the four categories so that I could quickly spot the highest level of certainty for a species.
LASBOR = Eastern Red Bat
LASINT = Northern Yellow Bat
LASNOC = Silver Haired Bat
LASSEM = Seminole Bat
This year, Highland Lakes Master Naturalist Bill Sewell created a program that further analyzes the data generated by KPro and automatically produces a report for the landowner. It also creates the summary file submitted to TPWD at the end of the season. A huge thank-you from all the bat-monitoring analysts to Bill for reducing what once took an hour or more per site to the click of a button.
The Bats
In Hays County, 14 bat species may be present. Eight are Species of Greatest Conservation Need (SGCN). One is considered Threatened. Three have an unknown conservation status in Texas, and two are Species of Least Concern.
Last year, the number of bat species detected at each site was highly dependent on the availability of water. Most landowners had eight to 10 bat species recorded on their property. I live in a community that doesn't have a stream, creek, or pond, and only four species were detected here.
This year, with the abundance of rain, a few sites have recorded 11 species. Rain can have the opposite effect on recordings as well, because bats generally do not forage during rain events and the rain itself is recorded as noise.
To support bats in your neck of the woods, plant native plants. These attract the insects that feed these flying mammals. Though you may not see or hear bats, our acoustic monitoring is proving that they are much more prevalent than many people realize.
Wildlife Acoustics has a grant program to help researchers afford the equipment and/or software to monitor and analyze bat calls. This is a quarterly grant program. Rachel Grotte, Texas Nature Tracker and project lead for the Bat Acoustic Monitoring Program, suggested that the bat acoustic monitoring coordinator for each TMN chapter apply.
It was quite a surprise to realize that I won the award for a software license for Kaleidoscope Pro worth $399. The license is available through the grant for one year. The state purchases licenses that we share between chapters. Having an additional license means more work can be accomplished in a shorter period of time.