Exploring The Last Green Valley: Gray tree frogs produce nightly lullabies

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Exploring The Last Green Valley: Gray tree frogs produce nightly lullabies

It was a chilly, sunny autumn morning when I discovered a frog in the grass below a maple tree in my yard. The cool weather had slowed its metabolism, and it hardly moved when I picked it up and held it in my hand. Its mottled gray and light brown color and round “suction cup” toe disks used for climbing identified it as the unique gray tree frog – Hyla versicolor.

I cupped my hands together until the warmth of my enclosed palms woke its senses. I felt it moving, opened my hands, and out he jumped back to the grass below the tree. I left it there to make its way to its winter habitat in the soil below the nearby shrubs and brambles.

These small frogs are only about 2.5-inches long and are well camouflaged to resemble the bark of trees, where they reside undetected by predators. But come the spring mating season, the males are very vocal with their loud rough trill heard in the evening.

These past few weeks, I have been reminded of that chilled tree frog by the seemingly constant loud calls of the males. One night last week, the sound was overwhelming and seemed to be coming from everywhere. I heard it within the tall trees lining our stonewall, from the tall wet grass of our back pasture and even far away in the boggy wetland of my neighbor’s woods.

I ventured outside into the moist, warm evening to listen to the frogs and record the sound of their calling. As I approached the trees along the stonewall the sound suddenly stopped, and with each step as I walked under the trees along the wall the frog songs ceased as I passed. When I reached the edge of the pasture, I could still hear the sound coming from further away in the tall grassy field and my neighbor’s wetlands. Clearly my presence near the trees had caught the attention of the elusive, shy singer of warm spring nights.

It is obvious to me we have an abundance of gray tree frogs this year. My guess is the increase in tree frog activity is a result of our wet spring. I emailed Peter Picone, wildlife biologist at Connecticut Department of Energy and Environmental Protection, and he confirmed increased moisture in spring and early summer will result in more tree frog activity. He also indicated he has been hearing more tree frogs on his own property.

The key word is “hearing” instead of “seeing” tree frogs. The single tree frog I found in my yard a few years ago is the only time I recall seeing one. Their ability to hide within their tree canopy habitat is the obvious reason I don’t often see them. My status as a “retired” climber of trees also keeps me from venturing into their arboreal home.

Here is some interesting information about the gray tree frog gleaned from the Stokes Nature Guide to Amphibians and Reptiles:

Adults are a mottled gray on the back and legs with bright yellow flash patches on the rear of their thighs. The large rounded toe disks, “suction cups” which help it climb, distinguish this species of tree frog.

In April the tree frogs emerge from overwintering in the ground beneath leaf litter or inside small burrows, and then they move to trees where they keep silent for several weeks. The males begin singing during warm days and then start to migrate to trees and horizontal branches near or above breeding ponds.

The males have three types of calls, the “advertisement” call, courtship call, and aggressive call used if another male is nearby. The sound we typically hear is the loud and prolonged trill of the advertisement call. This call has excellent carrying power and that certainly is true with the tree frogs at our house in Putnam.

Once the female has chosen a mate, the male and female will stay on the perch for several hours before she’ll move into the water to deposit her eggs. Groups of 10 to 40 eggs are scattered on the surface of the pond until almost 2,000 eggs are laid.

The eggs of gray treefrogs are light colored, gray above and white below and, generally, deposited in globular clusters. They hatch within two to five days of being laid. The tadpoles are only ¼-inch in length when hatched and grow to 2.5-inches with olive green body and distinctive brick red tail.

Newly metamorphosed gray treefrogs are small, about 1.5 inches in length, and are a beautiful bright green color.

According to DEEP, the gray tree frog is widely distributed but has been declining since the 1930s due to the loss of shrub swamps, their preferred breeding habitat. Their habitat loss is the result of draining of wetlands and the conversion of large tracts of shrub swampland into ponds and lakes.

According to DEEP, “this is a common development practice in many areas, driven by the legal mandate not to lose wetland acreage, but without regard for the vegetational structure, ecological function and biological complexity of the wetland. The wetlands that result from these conversions are usually biologically impoverished and serve as habitat for only the most hardy and adaptable amphibians and reptiles.”

The wet weather we experienced this spring has benefitted the gray tree frog. We are hearing more and more of them and hopefully that bodes well for this unique and fascinating amphibian of the trees.

If you’re interested in hearing the call of the gray tree frog you can find them on YouTube.

We live in a beautiful place called The Last Green Valley National Heritage Corridor. Our region is still 77 percent forest and fields, green during the day and dark at night. I hope you’ll join me and others as we care for, enjoy and pass it on.

Bill Reid is the chief ranger of The Last Green Valley National Heritage Corridor and has lived in the region for more than 35 years. He can be reached at bill@tlgv.org.

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