Monday, May 07, 2018

Mass Bat Emergence on My Third Visit to the Extreme Western End of the I-80 Yolo Causeway

These Mexican Free-Tail Bats are known for their big emergence displays in summer. I thought it was too early to expect one yesterday, but I was wrong! I got all kinds of ultrasonic bat recordings too. The supporting literature says the recordings are particularly unreliable during roost emergences, and indeed, the recording waveforms looked like static when a zillion bats appeared at once. Still the recordings I got are robust, with tons of bat signals.

I almost left too early and missed the emergence of the bats. It was amazing when it came! There were a couple of people from Concord nearby. As I walked away, the woman bid me stop. "Can you see the bats flying around under there?" she said. I thought she was nuts at first. It was more than thirty seconds before I finally saw movement. The mass emergence started less than a minute after that.

Next time, I'd like to be in a position to see the bats come out of their homes in the expansion joints under the I-80 freeway. And I wonder about all the solitary bats of other species left behind.

I like playing the bat recordings at 1/16 speed. Makes them sound like mysterious monkeys. This recording is labeled Canyon Bat, but since it was just a few minutes before the mass emergence, there are lots of other bats here too, and all very loud.

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