Frog chorus

  • A Green frog (Rana clamitans) peers out from a pond in Arrowsic, Maine. There are nine species of frogs in the state and this common frog lives in Maine ponds, breeds in the summer, and hibernates either in pond bottoms or underground during the winter. AP

  • A gray tree frog is seen at the Houston Zoo in 2008. AP file

For the Monitor
Saturday, July 01, 2017

Spring is usually the season associated with frog calls. It’s a thrill to hear the first spring peepers and wood frogs sending their songs into the chilly April evenings, assuring us that winter is really coming to an end. But that was months ago. We are in the heat of summer now and those frogs have long ago left their nuptial vernal pools and returned to the woods for a quiet summer.

But this is not true for all frogs. The male gray tree frogs are also most vocal during the spring mating season, beginning to call when the nighttime temperatures warm up to a minimum of 50 degrees. But, they can also be heard calling at various times of day or night in spring and through the summer. Humidity may influence their calling and they frequently call when the air is warm and steamy, such as before a thunderstorm.

The gray tree frogs are most often heard singing from high in the branches of mature trees. For this reason and because their loud resonating trill is somewhat bird-like, many people think their sound is actually coming from a bird. Trying to locate the source of the sound isn’t easy. These frogs are only 1 to 2 inches in length and are extremely well camouflaged. They are able to change color depending on the surface they are attached to. While clinging to the trunk of a big old maple tree, they are greyish-white, resembling lichen that grows on tree bark. On a darker surface they can be nearly black. When they are young, and spending more time among the leaves, they are bright green. Their scientific name reflects this ability, Hyla versicolor. The other reason the gray tree frog is hard to find is that their voice has a ventriloquist quality to it, so the sound appears to be coming from somewhere other than where the frog is perched. But even if you can’t find the frog, their sound is a fine addition to the summer soundscape.

Other “summer frogs” include the green frog and bullfrog. These species are similar in appearance. The adult bullfrog is the largest North American frog, measuring from 3 1/2 to 6 inches in length. The green frog ranges from 2 to 4 inches. When their size overlaps, the raised ridges on the back of the green frog help to distinguish them from each other. Another way to tell them apart is by their sounds.

As you walk along the edge of a pond or lake, you might here the single but repeated “plunk” call of the male green frog, resembling the plucking of a banjo string. The male bullfrog by contrast has a deep, multi-syllable call which can be paraphrased as “jug-o-rum.” Both will call from the emergent vegetation around the edge of a permanent body of water.

This makes them much easier to locate than the tree frogs, but you must still be a keen observer. They often float mostly submerged below the surface with just the eyes on the top of their heads poking up to watch for danger or food. If you do happen to get a close look, notice the size of the eyes in relation to the round circular ear membrane behind their eye. If the ear is larger than the eye, it’s a male frog, if it is smaller or the same size as the eye, it’s a female.

Of course if you see them sing, you can also distinguish the sexes. Only the males sing and when they do, they inflate their throat like a balloon to provide resonance for the sound they are making. The color of the throat is another field mark to observe. Males of both bull frogs and green frogs have yellow throats, the female’s throat is whitish.

While these three species of frogs are common, several other species of frogs found in our state such as the northern leopard frog and Fowler’s toad are classified by New Hampshire Fish and Game as species in greatest need of conservation. Visit the New Hampshire Fish and Game website and learn how you can help these species and others by recording sightings of them and following guidelines from the Wildlife Action Plan wildlife.state.nh.us/nongame.