50 years of bats and fog

There was fog in the Champlain Valley on Sunday night. At dusk I took a photo of the fog behind the house (Figure 1) and after dark started listening for bats with the Echo Meter Touch 2 bat detector plugged into my phone. During the next 45 minutes the phone recorded 70 bat calls. The fog became denser during the evening and was quite thick by 10:00 PM when bats were still calling (Figure 4). The phone app identified five different bat species including the usual suspects little brown bat, big brown bat, and silver-haired bat, but many of the calls were identified as Indiana bats or northern long-eared bats. That was the first time I had recorded more than a few Indiana bats or northern-long-eared bats anywhere other than at an Indiana bat maternity roosting colony. The phone app can confuse little brown, Indiana, and northern long-eared bats (they are all in the genus Myotis and have similar calls), but regardless there was a lot of bat activity on a rather foggy evening.

Figure 1. The forest from my backyard at 6:30 PM on Sunday October 3, 2021. At this place I used my phone to record 70 bat calls in 45 minutes. The fog became denser during the evening and was gone by morning. When the BLSG spray truck passes by, the roadside forest never looks like this. Within minutes of the spray truck passing, the pesticide mist disperses and becomes invisible, in part because ULV droplets are tiny compared to natural fog droplets and also because the ULV mist is less dense. After dark there were many bats flying through this fog and foraging for flying insects.
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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).
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