Salisbury Press

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PRESS PHOTO BY BUD COLE Male PRESS PHOTO BY BUD COLE Male "spring peeper" frog with its vocal sac filled with air sits camouflaged in a vernal pond.

Jeepers, creepers, it's 'spring peepers'

Wednesday, April 17, 2013 by The Press in Focus

There are many signs and sounds that announce the natural awakening of the spring season. Clues articulating the sounds and signs drawing our attention to visions of regeneration are everywhere.

In some years, like this one however, Old Man Winter tries to stick around well past the official first day of spring.

There is one harbinger of spring that does not worry about cold weather hanging on or a late falling snow because this critter produces antifreeze that protects it from the cold. These internally-produced chemicals allow this little critter to rebound from a sudden spring dip in temperatures that fall below freezing.

Perhaps you've heard what sounds like a chorus of crickets singing on spring afternoons and evenings. These songs, or should I say repeated notes, are sung by tiny elusive amphibians.

I've talked with individuals who thought they were hearing crickets, but these spring sounds are coming from small frogs that are so tiny and well camouflaged that they blend in with their habitat making them very difficult to find even when people search for them. It took me many years to finally snap a few photos of these sirens of spring. And with a swampy water background, the photos are often difficult to reproduce. In most cases they are known only by their sounds.

You might wonder what secretive musician emits these melodious sounds. It is the "spring peeper" and its call is familiar to millions across the eastern and central United States.

The spring peeper is a small frog not much more than one-inch long, but it has a powerful call. Early in spring, these chorus frogs gather in large groups in or near vernal pools calling back and forth as the sun begins to set.

Vernal pools or ponds are temporary areas of water that usually form from snow melt and spring rains and dry up in summer or fall. With the dry weather so far this spring many of the vernal pools that I'm familiar with are already dry.

A frog produces its call by moving air across a series of vocal cords. First, it fills its lungs with air. Then it closes the opening to its mouth and nostrils and pushes the air forward, inflating a vocal sac, or pouch.

The vocal sac, a balloon-like structure, is located at the lower bottom of the mouth. The air is moved back and forth between the lungs and the pouch. As the frog moves the air continuously over the vocal cords, the distinctive call is produced. Frog species' sounds may vary from croaks and grunts to trills and whistles.

The male spring peepers' call is a series of sharp, shrill bird-like peeps of a single clear note usually lasting about three seconds. This breeding call is repeated at intervals of about one second. Experts tend to agree that the calls are primarily used to attract females and that these breeding calls become infrequent to nonexistent after the spring reproduction season.

Specific calls are unique to members within the same frog species. This eliminates the possibility of females breeding with males from different species. The spring peepers continue to be active, but because of the silent period after mating it seems as if they have disappeared altogether.

Physical activity tapers off as fall temperatures begin to drop and the spring peepers' activity eventually slows to the point where it stops eating. Just before its heart and respiration functions drop to hibernation levels, the spring peeper digs down below the frost line to await warmer conditions. When conditions become favorable again in late winter and early spring, it returns to the surface.

The spring peeper and its cousins, the wood frog and the gray tree frog, leave their cozy hibernation areas months before other frog species. They have the unique ability to manufacture extra amounts of glycerol, a chemical that serves as natural antifreeze, thus preventing the frog's cells from freezing during very cold conditions. They survive subfreezing nights and extended cold periods that might occur after they emerge from hibernation.

The spring peepers, like all other amphibians, are cold-blooded, or ectothermic. Body temperature is derived from the temperature around them. Birds and mammals produce their own body heat and are not dependent upon external environmental temperatures.

The ectotherms regulate their body temperature by moving from place to place. When the area becomes too warm they move to a cooler spot. They move back and forth between shaded and sunny areas or into and out of water. This allows them to continually adjust their body temperature.

The spring peepers, like other tree frogs, have small toe pads that aid in movement for climbing and grasping. Tree frogs eat the same kinds of insects as do their terrestrial cousins. Frogs are carnivorous during their adult stage. Most species are stimulated to feed by the movement of their prey.

Be sure to listen for the spring peepers in your neck of the woods before they become silent for another year.

That's the way I see and hear it!

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