Friday, April 19, 2013

Mountain Chorus Frog

The timing of my trip into Shawnee State Forest last weekend was perfect for catching the short-lived eruption of breeding Mountain Chorus Frogs, Pseudacris brachyphona. This species is far more limited in its distribution in Ohio than is the more familiar Western Chorus Frog, P. triseriata, which occurs nearly statewide. The latter makes a characteristic grating rasp, often said to resemble the sound of a fingernail run down the teeth of a comb.

Mountain Chorus Frogs make more of a short bleating trill - faster and higher-pitched than the Westerns. They also occur in heavily wooded areas and are limited to the unglaciated hill country of southeastern Ohio. I've never heard Mountains and Westerns together, and doubt that their paths would typically cross given the differences in habitat.

The above photo shows a typical Mountain Chorus Frog breeding pond. These frogs are prone to selecting tiny ephemeral pools, often little more than water-filled tire ruts in some cases.

As I cruised the forest roads within Shawnee, the nasal bleating of chorus frogs was a routine part of the soundscape, and finally I had to stop and try and run some down. I caught up with a number of frogs in a tiny puddle, and at the expense of some wet and muddy knees, was able to procure some images. In this image and the following, the mating pair of frogs are about six inches under the water, which was crystal clear.

Like most other frog species, when a large human blunders near the mating pool, all of the frogs go silent and dive into the muck. With a little still and quiet patience, they'll soon pop back out and commence activities. This pair was so enthralled with one another that they never even hid, and I was able to sneak quite close without alarming them. The male (top, obviously) is locked in amplexus with the reddish-brown larger female. Note the length of her toe!

Other frogs in this pool had already mated, and freshly deposited eggs can be seen to the left of the frogs. In short order the egg clusters will expand into large gelatinous masses, and before long the pool will swarm with tiny tadpoles. I suspect that Mountain Chorus Frog tadpoles mature quickly, as many of their breeding pools dry up within a month or so after breeding season.

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