At the end, I am at home in the woods
More than a year ago I took a hike along the Green Mountain Escarpment (Vermont) in search of an old mine. I had read in an old report that Indiana bats hibernated in a mine in the area, and that was enough of an excuse to go exploring. I watched a bear and two cubs for 15 minutes but never found a mine. It was a pleasant hike along old logging roads through private property. No one lived on the several properties I traversed, none of which was posted.
After 12 nights of recording bat calls near an Indiana bat maternity 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.
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 maternity 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.
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.
A water depth data logger has been running unattended at a vernal pool (MLS619) at Snake Mountain in Bridport since April 10. The water was a meter deep when I waded out then to change the batteries and swap the microSD card. I have not been in a hurry to do the swap again assuming that the longer I wait the less wet I will get doing it. But I didn’t know how long the batteries would power the logger. The previous record was 11+ weeks, although a similar logger has been running in my office for more than a year on the same batteries. That one only saves data when certain conditions are met but it has been waking up every 30 minutes and sensing its environment for almost 13 months. I decided 16 weeks would make a good record for field deployment at MLS619 and was pleased to find that data had been written to the microSD card once every 30 minutes during those 3.7 months.
Some “then and now” sliders in the last post about Glacier Bay suggested that blueberry and hemlock were spreading in the understory at two of the older study sites we visited last month. Below I am trying out another method of displaying these pairs of old (1990 or 1995) and new (last month) photos. Some new photo pairs from York Creek and Beartrack Cove have been added as well as pairs from a third site.
Last month I was on a two week camping trip in Glacier Bay National Park collecting data from thirty-year-old study plots. We measured and counted the same things (tree diameters, number of alder stems) that we did in 1988, 1989, or 1990. I brought home lots of new data to compare to the old data, and also brought home 1600 new photographs.
The photos are of four types: repeat photos of the study plots, natural history, scenery, and photos of the field crew trying to look like it’s not raining.
About this time last year, our vernal pool near East Middlebury had been reduced to a puddle by some warm and dry weeks in May. According to our data logger, it was completely dry on June 16. 2020. This year the pool might be dry a little earlier than last year.
In addition to the HOBO temperature logger in each vernal pool, we have a water depth data logger installed in the two pools we are watching this year. We have looked at the data from late January to early April and the loggers are continually recording new data every 30 minutes.
Ned and I have been monitoring a second vernal pool this year. The new pool is in Bridport on the southern extension of Snake Mountain. It is right in the middle of the Champlain Valley, but up on a rocky ridge. The pool is almost twice a big as our other one and a foot deeper. It is lower in elevation at 570 feet above sea level (the other one is in the foothills of the Green Mountains at 1260 feet a.s.l.).
The most important difference between the two pools might be chemical. The new pool sits between two ledges of Middle Cambrian dolostone or dolomitic quartzite, limey rocks which enrich the soil with calcium and magnesium. The old pool is surrounded by Cheshire quartzite and the vegetation there (red oak, beech, birch) suggests that the soils are not rich in calcium.
The vernal pool we have been monitoring has been dry since about June 17. There were a couple of rainy days in late June, but the puddles formed did not last more than a day. The pool was dry when I visited on July 10, September 29, and October 23. That is, there was no standing water, but the soil under the leaves was always damp. New data from the water depth datalogger indicate that only two rainfall events between June 30 and October 23 produced standing water in the pool.
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.
