Listening for Bats: Acoustic Monitoring at Glacier Bay National Park

Glacier Bay National Park and Preserve, in Southeast Alaska, wants to know which bats live where in the park — and it finds them by listening. Bats in the region are not well studied, and understanding these migratory mammals across the country helps protect them from threats such as white-nose syndrome, a fungal disease harming bat populations nationwide.

A researcher holds a Long-eared Myotis as part of an NPS research study in Alaska. NPS Photo.

The silver-haired bat (Lasionycteris noctivagans), one of the species detected in Glacier Bay. NPS photo.

Finding bats by sound

Bats echolocate: they bounce sound off objects to find insects and avoid obstacles in flight. That same habit lets scientists find the bats. An acoustic bat detector is a microphone and recorder that switches on at dusk, records bat calls through the night, and shuts off in the morning. Some calls are loud enough for people to hear, but many are ultrasonic — every Alaskan bat species calls above the range of human hearing, with only the lowest notes dipping just below 20,000 hertz — so a special microphone is needed.

Each species’ calls differ in frequency and pattern, so researchers can read sonograms, pictures of sound, to tell which bats flew past.

The method has big advantages: it is automated, the equipment can be left out for weeks, and it is non-invasive — the bats are never disturbed.

A detector microphone hung in a tree in Glacier Bay. NPS photo.

How the study works

Researchers put out detectors in late spring and monitor through fall, in both the park’s developed front country and its backcountry, from 2017 onward. Sites are chosen near water or where bats have already been seen. Microphones and recorders are fixed to trees and set to run from dusk to dawn, alongside loggers that track water and temperature. Crews check the setups during the season to change batteries, and at season’s end the recordings are analyzed to see which bats pass through, when they are most active, and which ones use an area most.

What they have found

By 2023, recordings had confirmed five bat species in the park:

• silver-haired bat (Lasionycteris noctivagans);
• little brown bat (Myotis lucifugus);
• long-legged myotis (Myotis volans);
• long-eared myotis (Myotis evotis); and
• California myotis (Myotis californicus).

An acoustic detector deployed in Glacier Bay’s front country. NPS photo/ S. Elizarraras.

All five turned up in the backcountry; four were confirmed around Bartlett Cove, the developed area, where the long-eared myotis may also be present. Activity peaked in July and August in the front country and in August and September in the backcountry. The species recorded most often were the little brown bat, silver-haired bat and long-legged myotis — and the little brown bat is also the one people see most.

A little brown bat (Myotis lucifugus). NPS photo.

The park hopes to add more detector sites across its vast area.

Sources

Based on "Bat Acoustic Monitoring at Glacier Bay National Park and Preserve," Glacier Bay National Park and Preserve, National Park Service; a work of the United States government in the public domain. Pictures an earlier version of this page left out were restored on 2026-09-26.