It’s Not Easy Being Gray
Though autumn is here, let’s look back at just a few weeks ago, when the hot days of summer had taken hold and even the woods and fields which were normally filled with sound and motion got quiet and still.
The occasional bird song or cicada call echoed through the air and a grasshopper or butterfly might venture out on the wing to take short flights. Even our amphibian friends around the pond had grown more hushed in the heat of those sweltering days. Another frog, away from the pond, was heard and seen. Whether drowned out by its more vocal and conspicuous kin, this frog is easily overlooked. But not today and not as we take walk in the wood at Harmony Hill.
Away from the waters of the pond, we encounter treefrogs. The one species of treefrog (Family Hylidae) we have documented so far at Harmony Hill is the Cope’s Gray Treefrog (Hyla chrysoscelis). We’ve been hearing their trill vocalizations throughout the summer, echoing from upland pine forests to bottomland hardwoods. Quite often, we hear them call from their perches in trees during the lazy warm days, but they tend to do most of their singing once the day has begun to give way to evening time. To many, the call of this frog is often written off as background noise. And their cryptic colors and patterns mean they aren’t the most eye-catching frog at Harmony Hill. However, if you’ve joined us for even one walk in the wood, you know we don’t simply write anything off as background noise and we find beauty and fascination in all flora and fauna on this beautiful landscape.
Why don’t we begin by looking at the namesake of the Cope’s Gray Treefrog? Edward Drinker Cope (1840-1897) was an American naturalist from Philadelphia. Known for his knowledge and passion for everything from frogs and fish to fossils and physiology, Cope was mostly self-taught and looked for nearly any excuse to get outside to study nature. Driven by curiosity, Cope was keenly interested in paleontology. His demeaner, determination, and approaches were known to cause problems in his personality and character, even blinding him to the humanity and ability of others. It is for him that this mostly gray-colored and mottled tree frog is named.
The genus name of Hyla means “wood”, “forest” or “timber”. This is a clear reference to the members of this genus being found in trees. Chryso is the Greek word meaning “gold”, while kelis is the Greek word for “stain” or “a spot”. Combining those two words gives us the species name of chrysoscelis, referencing both the metallic sparkling found in the granular skin of the frog and the bright gold-orange coloration hidden on the inner thigh of the frog.
Cope’s Gray Treefrogs depend on their cryptic colors and pattern to provide extremely effective camouflage to hide from predators. Whether found perched on pine, holly, oak, or hickory trees, they blend in and look like little more than a bump or knot on the trunk or limb. If discovered; however, they will leap away at the last minute, displaying the flash of orange on the inside of their groin. This flash of color serves as a distraction to potential predators, causing a cautious pause and allowing the frog to escape.
Like other frogs, being an amphibian, Cope’s Gray Treefrogs are dependent upon water for reproduction. Males will find a pond or ephemeral wet area, one without fish whenever possible, and begin calling from somewhere high up in a tree. At Harmony Hill, there happens to be just such areas found in various habitats around the property. The two separate Cope’s shown in the photographs this week were found not too far from wet areas that have been drying in the recent weeks.
When the females arrive to investigate the singing, the males maneuver down the tree to the ground, where they mate. The females later lay their eggs in “packets” of between 30-40 eggs and attach them to vegetation in the pond or wet area. Hatch times and tadpole development times are entirely dependent upon water temperatures. Under most summertime conditions at Harmony Hill, the time from the egg hatch to tadpoles and, finally, metamorphosis to Cope’s Gray Treefrogs emerging from the water usually spans a timeframe of 45-60 days.
Cope’s Gray Treefrogs are physically identical to Gray Treefrogs (Hyla versacolor) and should never be identified by appearance alone. For many years, they were thought to be the same species, perhaps simply being two subspecies of the same species. Genetic research and DNA sampling proved them to be separate from one another.
But, if they look just alike and we don’t have DNA laboratories at Harmony Hill, how are we to distinguish them as Cope’s Gray Treefrogs or Gray Treefrogs? We have a wonderful tip for you!
The calls of the two frogs are quite different and provide a definitive way to identify the two species. The calls are also different enough that females of the two species do not tend to mate with a male of the other species. And if you’re wondering what that difference is, well the trill of the Cope’s is faster than the trill of the Eastern. If you ever have the chance to hear both species, the difference is pronounced enough that you can confidently tell them apart once you learn them. And, since you’re all our fellow naturalists, we believe in your identification abilities!
The genetic research we mentioned that led to the separation of the two species also led to the discovery that Cope’s Gray Treefrogs have diploid chromosomes, or two sets of chromosomes in each cell nuclei. Their relative, the Gray Treefrog, has tetraploid chromosomes, or four sets of chromosomes in each cell nuclei.
Before we part company this week, there’s one last cool fact about Cope’s Gray Treefrogs. They are capable of secreting a slightly toxic substance from their skin. While this toxin will not harm you directly if you handle a Cope’s Gray Treefrog, please be absolutely certain to wash your hands thoroughly after you handle this, or any, frog species. As a matter of fact, let’s make that a rule after handling any wild animal!
This toxic skin secretion from Cope’s Gray Treefrogs is known to irritate eyes, mouths, mucus lining of noses, and open wounds of mammals. Humans can be especially sensitive to the secretion and it is an effective deterrent to predation. To avoid forgetfully wiping your eyes or nose and having a potential reaction, be very careful and mindful while handling the frog and please wash your hands well immediately when done.