Reflections in Nature:Gray treefrog not always gray

Bob Bastion, of East Troy, recently called to ask if I could identify a frog that his grandson caught. The frog was found hanging on the side of their air conditioner. So, with the state Fish and Boat Commission’s book, “Amphibians and Reptiles,” in hand, I went to their home.

At first glance, it was easy to see the frog was one of Pennsylvania’s tree frogs because what appeared as large suction cups were on the bottom of the frog’s toes; however, identification became more difficult after that.

The book stated that the round sticky toe pads aid the frogs when climbing and also enable them to adhere to windows, which are adjacent to porch lights, to catch insects.

After eliminating quite a few frogs, I was able to identify the frog as the Eastern gray treefrog. However, I still was confused because this frog was green and not gray.

The Eastern gray treefrog’s scientific name is Hyla versicolor versicolor. As the scientific name implies, the gray tree frogs are variable in color because they have the ability to camouflage themselves from gray to green, depending on what they are sitting on.

However, they change colors at a much slower rate than a chameleon. One source stated that it takes about 30 minutes for the frog to change colors. This tree frog can be green, gray or brownish in color.

The Eastern gray treefrog, which is found all across Pennsylvania, is most common in forested areas where their calls often are heard. It spends the day either beneath the loose bark of a tree, in a hollow of a tree or clinging to the trunk or branch of a tree, where its colors and pattern create a natural camouflage, blending in with the bark.

For an easy identification of this species, check the thighs of the hind legs of the males, which will be a bright yellow-orange on their inside and underside; however, these areas are usually concealed from view and only visible while the frog is jumping.

In the females, the under part of the legs are pale olive green in color.

Breeding season is in the spring when nighttime temperatures begin to warm. At this time, the Eastern gray treefrog climbs from his perch to join others in a chorus, which signals the beginning of the mating season.

Compared to the spring peepers, tree frogs rarely have large choruses; however, the males might vocalize competitively at the height of the breeding season. This is about the only time the Eastern gray treefrog can be seen on the ground.

Mating occurs between April and August, with the later months probably the time when most treefrogs enter the water. The male grabs the female around her chest with his front legs and clings to her until she releases her eggs, which then are fertilized by the male.

The female can lay 700 to 3,800 eggs, usually in small floating groups of 40 eggs each. The brown and cream-colored eggs hatch in a few days.

The tadpoles that emerge from the eggs are a golden color, with a red to orange-red tail. In six to eight weeks, the tadpoles metamorphose into young frogs.

The young frogs, which are a greenish color at this stage and about a half-inch long, will stay close to the water. By the end of summer, they will go to nearby trees and bushes. It is an adaptable frog because it is often found in populated areas and around homes.

I’m sure most of us have heard the calling of the Eastern treefrog. The call is almost flute-like, somewhat compared to the American toad. It is described as a short trill of one to three seconds, performed several times in succession.

During spring, the frog calls mostly through the night, and in early summer, the frog calls at either dusk or after a summer rain. However, individuals often are heard calling during the daytime in response to thunder or other loud noises. The call comes from a single throat sac, which is a large inflated bubble. The female, which is larger than the male, does not call. She has a white throat, while the male has a black/gray throat.

During the winter months, this tree frog actually freezes. It survives by producing large amounts of glycerol, which is changed to glucose and then circulated throughout the frog’s cells. This glucose acts as an antifreeze and prevents ice crystals from forming in the cells. The remainder of the frog’s body freezes, and its heartbeat and breathing stop. When temperatures warm up in the spring, the tree frog thaws out.

Bower retired after 34 years as a wildlife conservation officer for the state Game Commission. He has published several books about his experiences. Questions and comments may be sent to him at 153 Redington Ave., Troy PA 16947.