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.
Southern Leopard Frog
Last weekend, Jasmine uploaded three photos of a frog encountered at Harmony Hill (see the previous post in this channel). This frog is one that can be a bit confusing to identify by sight, but this species is almost unmistakable by voice.
Why would this species be confusing to identify by sight? That is the most important question to answer and, when we answer that question, removing the confusion will make this frog MUCH EASIER to identify!
This species sort of looks like another species or two found in the same genus, but there are field markings that differentiate this species. This species of frog also comes in a WIDE variety of colorations, all in the brown to green spectrum. Some individuals are all brown, with spots. However, some individuals are all green, with spots. And there are quite a lot of individuals that are gradients of brownish/greenish over different parts of their bodies, with spots! AND, as if that weren’t enough confusion, the spots can be various shapes and sizes!
Now that we’ve introduced as much confusion as we can, let’s start clearing the clouded waters. Let’s look at the constants that we can look at to identify this species. Found on this species of frog are prominent, light colored ridges on each side of its back that start just behind each eye. Furthermore, there is a light band in each eye that extends onto the light ridges on the back.
Next, let’s look at the tympanum (or external eardrum) seen just below and behind the eyes. A definitive field mark to look for on the tympanum is a light-colored dot right in the middle. (I’ve included a closeup of one of Jasmine’s photos that highlight this field marking. I have placed a red arrow pointing to the dot in the middle of the tympanum.)
This species also has a pale upper lip and belongs to the family Ranidae, the true frogs.
Having covered what to look for to identify this species, that leaves one major question… Well, Josh, what is it?! It’s a Southern Leopard Frog (Lithobates sphenocephalus)! Those spots that show up on all members of this species are responsible for their common name. They’re spotted, like a leopard.
There are some who still list the scientific name of this species as (Rana sphenocephalus). It’s also not uncommon to see it listed with both genus names and have it written as (Lithobates [Rana] sphenocephalus). What’s that all about?
The older genus name, Rana, is a direct link to the name of the true frog family of Ranidae. Rana and Ranidae are different names indicating “true frogs”. The new genus name, Lithobates, is Greek for “rock walker” (Litho, meaning stone and Bates, meaning one who walks upon.) Their species name, sphenocephalus, means “head shaped like a wedge”. I’ve placed a red circle on the snout of the photo to highlight that pointed nose.
There are 8 other members of the genus, Lithobates (or still listed as Rana), in South Carolina. However, Harmony Hill is definitively in the range of two other species in this genus, Bullfrog and Green Frog. The land is potentially in the range of three other species in this genus, Carpenter Frog, Gopher Frog and River Frog.
As an amphibian, Southern Leopard Frogs are tied to water. To lay eggs and to keep their skins moist, they must be in the vicinity of water. Their eggs have to be laid in water and, with this species, that water is most likely shallow water that has little predation (usually fish). They also lay their eggs so that they’re anchored to some vegetation. However, Southern Leopard Frogs are often found quite some distance from water. While doing the snake research at Carolina Sandhills NWR, I regularly found Southern Leopard Frogs over half-a-mile from standing water. So, don’t be surprised if you encounter them away from where you might expect them!
Their diets are pretty varied, including any insects or invertebrates that might fit in their mouths. I’ve seen them munching away on crayfish. Their especially fond of crayfish that have recently molted. With that varied diet, Southern Leopard Frogs are apt to be active anytime of the day or night.
As for that unmistakable call… I’ve always said it reminds me of the sound of a balloon being twisted, much like the sound you might hear when a clown is making balloon animals. I’m attaching a YouTube video of their call for you to listen to. What do you think? Do you agree with me? Does the call sound like a balloon being rubbed or twisted to you?
No other frog in the Harmony Hill area sounds like the Southern Leopard Frog. With that in mind, this is a GREAT species to begin our toad and frog journey as we learn a little more about the Story of the Land. When you see those light-colored ridges, those dots in the middle of each tympanum, that pointed snout, those spots and when you hear that twisted balloon croak, you have Southern Leopard Frogs on the land!
As I’ve made a concerted effort to do in previous posts, I’ve also made sure to look into a species that can also be found easily in Florida. And Southern Leopard Frogs can be found throughout the Sunshine State.