Frogs!

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 calls, very infrequently, and I couldn't really see where the sound was coming from (no obviously inflated pouches).

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 Ilike the leopard frogs, emitting sort of a quacking call that sounds like it should be coming from a duck.

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.

wood frog, Rana sylvatica

Here the wood frog has inflated its vocal sacs during its "quack" call.

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.

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.

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.

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.

More sounds of spring

The eve of the first (real) day of spring this year brought a good rain, and suddenly the ponds are alive with sound.  Within the space of just a few days of warm weather, the pond went from looking like this (five days ago):

where warm surface temperatures resulted in a massive production of duckweed, even on the ice itself

to completely open water.  In the (far) backyard we have a temporary (overflow) pond and two permanent ones, but the action today was concentrated in the temporary pond, where males of two species of frogs were loudly proclaiming their studliness to any listening females.  The Western Chorus Frog and the Wood Frog are the two earliest breeding frog species in most areas of North America.  Males invade the open water even before it is completely ice free, but they didn’t start calling in my backyard until yesterday.

Western Chorus Frogs are tiny little things (about an inch long), but incredibly loud, in fact almost deafening when you are standing right over them trying to find them in the weeds.  They look and sound like this: http://www.youtube.com/watch?v=oNbzSLa5fxQ

Not to be confused with their close relative, the Spring Peepers that will show up very soon and look and sound like this:

Chorus frogs prefer permanent water so it is surprising that they were calling from the temporary pond instead of the permanent one.  Their call resembles the sound you get when you run your thumb over a comb.  Males seem to call almost continuously which, at the volume they project, must be very energetically expensive.  The call rate (per minute) is temperature dependent, so if it’s a warm day or night, they might be calling up to 90 times a minute!

Wood Frogs were also calling in the temporary pond today, with about a dozen males jockeying for position along one shoreline.  They sound more like a group of ducks quacking than frogs.  Because they sit so low in the water, with just their head out, you have to find them by watching for ripples from the movement of their vocal sacs.

Males faced off, grabbed at each other, swam at each other, and climbed over each other while I watched them today.  I don’t know if the females have come to the pond yet or not, but if there is successful reproduction ovenight, then I should be able to find egg masses tomorrow.

Male wood frogs are smaller than females, but are able to hold on to the female with their enlarged forearms and thumbs during their hour-long mating (you can see this guy’s big forearms through the water in the photo below).

Because they breed so early in the spring, when normally they might face a few more snow storms or delayed ice melt, Wood Frogs ensure that their eggs and embryos resist freezing the same way that adults resist freezing over the winter, using antifreeze compounds.  They prefer temporary ponds because that ensures that their offspring will not be gobbled up by fish predators.  On the other hand, the transient water supply means that wood frog embryos must develop quickly before the pond dries up.

True to their name wood frogs retreat to the moist forest litter after breeding, and metamorphosed froglets will do the same as their pond begins to evaporate.

Video of mating wood frogs from Michael Benard (http://www.mister-toad.com/photos/frog/rana_sylvatica_03.html):