I went under the western end of the Interstate 80 Yolo Causeway, shortly before sunset. The device was flagging about 2/3 of the bat calls as Hoary Bats, and the remainder as the expected Mexican Freetail Bats.
I eventually attracted the attention of a Wildlife Area volunteer. He explained that there were a number of different bats here, but that the main body of mature Mexican Freetail Bats were at the eastern end of the Causeway. Later in the year, juveniles would move out here towards the western end. Both ends have spectacular and distracting bat displays at sunset in the summer. I don’t know why the juveniles would choose to live apart from their elders. Maybe their ultrasonic rock and roll grates on the ears of their parents.
I never saw any bats, but I knew they were there. I could hear them a bit. Something whirred past my head. I looked up and saw midges floating above me. If I attract insects, it’s logical I’d attract bats too.
As I left the Causeway in the gloaming, in the distance, I could see a midge tower forming. In June 2011, I saw a spectacular series of midge towers out here. I hope they come back.
Now, time to look into the spectral analysis software.