Chorus Frog Mystery

by Carl Strang

Yesterday was warm, and as I enjoyed my lunch break walk I heard 3 different chorus frogs calling in 3 different places. One was on top of one of Mayslake Forest Preserve’s hilltops.

One was in the middle of a meadow, far from water.

The third was close to the stream corridor marsh, where most of the preserve’s chorus frogs gathered last spring.

Their calling reminded me of the spring peeper mystery I described in an earlier post. The circumstances are a little different, in that chorus frogs’ fall voices are much closer to their sound when advertising for mates in spring. Also, instead of calling over a period of weeks to months, they have a more abbreviated period of autumnal calling. A year ago I heard just one at Mayslake, also calling from an elevated spot late in the season. As was the case with the spring peepers, I have not encountered an explanation for this behavior. The only possibility that has come to mind so far is that this might have something to do with finding a safe place to hibernate. The calling frog may be advertising the discovery of such a spot, or announcing the need for help in finding one. I’m not a theoretical evolutionary ecologist, but I don’t think kin selection needs to be invoked here. If these males help females survive the winter they are helping themselves, even if other males also respond. That’s the best speculative stab I’ve been able to come up with so far.

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