Comparing Bat Recordings from Different Microphones

Bats are hard to study. They are small, fast and active at night — but they depend on sound to communicate and find their way, so researchers often study them by listening.

A common method is passive acoustic monitoring: microphones are left in the field to record the calls bats make, with no observer present. The catch is that microphones exposed to the weather day after day often need to be replaced or updated, and a new microphone can change the type and quality of the data collected. That makes it hard to compare recordings made on different equipment — a real problem for monitoring that is meant to track bats over many years.

Setting up an ultrasonic microphone for acoustic bat monitoring at Apostle Islands National Lakeshore (NPS).

What the study compared

A study published in the Wildlife Society Bulletin in September 2024 put two kinds of ultrasonic microphones side by side in the field. The researchers looked at how often each detected bat calls and how easily the species on each recording could be identified.

One model clearly came out ahead: 70 percent of its recordings could be classified to species, compared with 61 percent for the other.

Why it matters

The researchers proposed a correction factor that allows data from the two models to be compared — the aim, as the study's title puts it, being to make long-term acoustic bat monitoring data easier to analyze.

Sources

• National Park Service, Park Science magazine, Research Roundup, Volume 39, Number 1 (Winter 2024–25): "A Way to Compare Mismatched Acoustic Data."
• Goodwin and others. 2024. "Comparing Field Performance of Ultrasonic Microphones to Facilitate Analysis of Long-Term Acoustic Bat Monitoring Data." Wildlife Society Bulletin e1547.