Being my favorite species of frog, the Gray Treefrog may get more than its fair share of exposure on the Naturally Curious blog. This amphibian is rarely noticed outside of its June mating season, when the males’ bird-like trills can be heard throughout the night from shrubbery bordering wetlands. Due to its emerald green coloration when young, and its mottled gray/green adult appearance, in addition to its nocturnal habits, this beguiling amphibian escapes detection by most of us throughout the rest of the summer.
However, if you keep an eye out in August, near where you heard those trills in June, you may be successful in spotting a juvenile Gray Treefrog. Having developed legs and lungs, absorbed their gills and tails, and reinvented their digestive system for insects, not plants, they are now permanently terrestrial, except during the breeding season. When a Gray Treefrog is young and newly metamorphosed, it usually remains near the forest floor. As it ages, it may transition to living in the forest canopy. (Photo: juvenile Gray Treefrog; inset – adult Gray Treefrog)
If there is an amphibian that is a master of disguise, it has to be the Gray Treefrog (Hyla versicolor). This remarkable frog is capable of changing its color (gray, green or brown) to match its environment within half an hour, a process called metachrosis. Shades of gray are most common with black blotches on the back while green colors are more prominent during the breeding season and in yearling frogs.
Being a treefrog, it has large, round, sticky toe pads that help it cling to trees and shrubs, where it spends most of its time. Survival is more likely if predators don’t detect you, so Gray Treefrogs have evolved to look a lot like bark.
When the temperature reaches 59° F. the males’ bird-like trilling can be heard coming from foliage next to and hanging over their shallow breeding pools. If you wish to set eyes on a Gray Treefrog, now is the time, as they are calling and a silent Gray Treefrog can be extremely difficult to find!
Congratulations to Naturally Curious readers for their familiarity with Eastern Gray Treefrog (Hyla versicolor) toe pads! This is the easiest time of year to find these amphibians, mainly because of their habits. During the fall, winter and spring treefrogs are usually silent, unlike the summer, when males can be heard calling their melodic trill from bushes and trees near bodies of water after the evening air temperature rises above 59°F. Because they are nocturnal, well camouflaged, and hibernate in the winter, you don’t often come across one except for the warmer months when males are calling. The colors of an Eastern Gray Treefrog (brown, green and pearl-gray) vary with the colors of its background and environmental factors such as season and humidity, but shades of gray are most common. Their green color is more prominent during the breeding season and in young frogs.
When hunting insects, or when disturbed, treefrogs can leap great distances and, thanks to advanced toe pads, when they land they can cling to practically any surface, including vertical branches and leaves that are wet. A very low angle between the toe pads and substrate as well as mucous glands located in channels between the hexagonal pattern on a treefrog’s toe pads have inspired the design for treads on car tires.
You can listen to an Eastern Gray Treefrog’s call by going to http://langelliott.com/calls-of-frogs-and-toads-of-the-northeast/ (Sound recording © Lang Elliott – langelliott.com)
Frogs and toads that hatched from eggs laid this past spring are now two to four months old, and are growing rapidly. Like snakes, frogs and toads shed their skin as they grow — unlike snakes, they eat their skin. Periodically toads and frogs stretch their bodies and then pull their loosened skin off in one piece, much like we pull off a sweater. Using their feet, they then stuff their skin under their tongue and swallow it. When frogs and toads are young and growing fast, they usually shed their skin more often than when they are older and their growth slows down. Not only is their skin a valuable source of nutrients and protein, but if it’s eaten, there is no sign left behind for predators to find.
Most young toads and frogs, with the exception of the Gray Treefrog, look like miniature adults. (Gray Treefrogs are emerald green in their youth, unlike the mottled gray/green adults they will become.) There is one characteristic at this stage that they don’t share with their elders, however, and that is their snub noses. If you’re wondering if the frog or toad you saw is a small adult or a youngster, take a closer look at its nose! If it’s unusually short and blunt, there’s a bit of growing left to do.
At this time of year, bird-like trills are often heard in wetlands, where male gray treefrogs (Hyla versicolor) are calling to potential mates. The chorus ramps up at night, but the songsters can be hard to find during the day, when they often hide in tree cavities or high up in the canopy. (Their large toe pads produce mucous which allows them to adhere to smooth bark.) The colors of a gray treefrog vary with the colors of its background and environmental factors such as season and humidity, but shades of gray are most common, with black blotches on the back. Variations of brown, green, and pearl-gray colors have been noted, with green being more prominent during the breeding season. Warm, humid weather seems to elicit calls from these well-camouflaged amphibians. To watch and hear a calling gray treefrog, go to http://www.youtube.com/watch?v=2kd5c4p8-0M. (Thanks to Rachael Cohen for photo op.)