Off and on rainy days with warm(er) temperatures have really set the frogs in motion here. I sat on an upended bucket by one of the ponds in the backyard and trained my binoculars on the pond’s edge, hoping to finally locate those tiny little creatures that were making that hugely loud racket.
Eventually, by trying to ignore the loudest chirpers, I could distinguish three different types of calls, all at different pitches, frequencies, and volume. Finally, by staring at the water where I thought the calls were coming from (this takes sound localization ability, which apparently I am lousy at), I found the frogs making them.
Leopard frogs made very low intensity, low pitch calls, and call very infrequently. I couldn’t really see where the sound was coming from (no obviously inflated pouches).
Wood frogs sit horizontally in the water, like the leopard frogs, emitting sort of a quacking call that sounds like it should be coming from a duck. Dark bodies, striped legs, and a black mask over the eyes outlined with white stripes — make this frog quite attractive.
Here the wood frog has inflated its vocal sacs during its “quack” call. When they do this, the water around them shows disturbances in concentric circles, making them a little easier to find in the pond (if you have bad sound localization ability).
Wood frogs are found almost everywhere in central and eastern North America; they are one of the first frogs out in the spring, as soon as the ice melts off the ponds. They are unique in that they tolerate being frozen solid over the winter, as they “hibernate” in a state of suspended metabolism under the leaf litter. Click here to view a short video of wood frogs calling (in Minnesota). And here is an amazing video of Wood Frogs defrosting from their frozen winter state.
By far, the loudest, shrillest, and almost deafening calls were coming from the Boreal Chorus Frogs (Pseudacris maculata), which were almost impossible to find, mostly because I was looking in the wrong places. They were sitting at least 3 feet from the shore, out in the submerged vegetation, oriented vertically, with their head, vocal sacs and abdomen out of the water. Perhaps the volume of noise from multiple frogs confuses predators as well. Are herons and egrets immune to this racket?
Even maximum telephoto didn’t bring these tiny, one-inch Chorus frogs into view.
So, I moved to a better viewing spot, sat, and waited until they got used to my presence, and then got closer-up views of a calling Chorus Frog. These frogs (once you see them) are easily distinguished by the three longitudinal stripes down their backs.
The cricket-like call is emitted through the larynx (voice box), but is amplified by vocal sacs. The body cavity of the frog swells when air is inhaled through the nostrils, and the vocal sac shrinks.
Then, the frog contracts its muscles to expel the air during exhalation through the larynx, enlarging the vocal sac, and producing a vibration that amplifies the sound.
If you haven’t had the pleasure of standing next to a group of calling Chorus Frogs, you can view a short video here. These tiny frogs can emit sound at nearly 90 decibels, which is about as loud as the human ear can stand without damage, about the same as standing next to a truck without a muffler. And, they call continuously for hours and days on end. Now how is that for amazing!
For good photos and descriptions of MN frogs and toads, you can click here.