Tag: bats

More noise, fewer bats

After 12 nights of recording bat calls near an Indiana bat maternal roosting colony, we deployed the AudioMoths for a week at the vernal pool where we recorded bat calls in August. Instead of putting two AudioMoths at the vernal pool, we put one by the pool and two in the forest surrounding the pool. One of the forest AudioMoths recorded nothing (a battery was inserted backwards), so we got data from only one non-pool AudioMoth.

Figure 1. Vernal pool MLS619 (Bridport, VT) on September 23, 2021 at the end of a week of recording bat calls. There was no standing water in the pool but the liquid mud was 6 inches deep. This might be as low as the water level gets in the pool this year (it was dry and firm last October). There were a few inches of water in the pool at the beginning of the AudioMoth recording on September 16.

Maternal roosting

Indiana bats live throughout the US Midwest and into New England. In winter they gather in a small number of caves where as many as 50,000 bats may hibernate together. This makes the population vulnerable to vandalism and since 1967 the Indiana bat has been on the US endangered species list. It was listed as Vermont’s first endangered species in 1972. Communal hibernation also makes bats vulnerable to the spread of white-nose syndrome and Indiana bat populations have declined moderately since the disease appeared in 2006.

Vermont is at the northeastern edge of the Indiana bat’s range where it has been observed foraging and raising young throughout the southern Champlain Valley. About 10 maternal roosting colonies where females raise their pups have been documented in Addison County. Female bats select forested sites with large trees and spend the day under loose bark with their single pups and forage at night for flying insects within two or three miles of the roosting trees.

Figure 1. A shagbark hickory tree (Carya ovata) near the site of a known maternal roosting colony of the Indiana bat in Addison County. Female bats and their pups spend the day under the loose bark on living and dead trees of this and other species.

Sound data

Part of the Vermont Center for Ecosystem Studies Vernal Pool Monitoring Project includes audio recordings to document the first calls of frogs at the pools. This year they started using AudioMoths to make the recordings. AudioMoths are open-source data loggers with a low-power sleep mode, real-time clock, microSD card slot, MEMS microphone, and circuitry to support audio capture. AudioMoths can be configured to automatically save audio recordings on a custom schedule. The AudioMoth software and hardware are well thought out and the audio quality is very good (see audio file below). The AudioMoths were deployed at about 50 Vermont vernal pools in weather-tight cases (Figure 1) and recorded for a few short sessions every night for several weeks in the spring.

Figure 1. The AudioMoth in a weather-proof case deployed at vernal pool NEW370 (near East Middlebury) between March 13 and May 8, 2021. It was configured to record for 10 minutes four times every night and save the wav files to a microSD card. The white plastic and foam is a rain hat which kept the AudioMoth drier but might have amplified the sound of big rain drops hitting it. April 11, 2021.

Bat plus ultra

This summer there was a bat or two flying over the yard every evening, so I started lying in wait for them with a camera. For about 15 minutes at dusk there was enough light to capture a bat silhouette if I used a good DSLR at the highest ISO. The photos were fun, but you can’t tell what kind of bats they are from the photos. Someone suggested using a bat detector — an ultrasonic microphone that listens to the otherwise silent calls of bats and even suggests which species are calling.

Unidentified bat in pursuit of a dragonfly in my yard at 8:24 PM on August 8, 2020. Nikon D3100, Nikkor 1:2.5 105mm lens, 1/2000 second, f/2.5, ISO 12800 (Hi2).