Hunting the loud but elusive Gray Treefrog
On many occasions, I’ve searched high and low for wild animals, only to turn around and find them staring at me. I get the feeling they’re laughing at me; they certainly can get me to laugh at myself. That was the case one fine June day this year when I encountered a little frog I had been looking for for days.
A male Gray Treefrog (Hyla versicolor) had been calling from the copse a few feet from my deck, with two or three more of the same species calling further off in the surrounding forest. Although Thomas Tyning, in the Stokes’ A Guide to Amphibians and Reptiles, talks about being ignored when he observed males of the species when they were calling, I’ve often gone on hunts to try to track one down, only to have him fall silent when I get close.
The Gray Treefrog looks almost identical to the less-common Cope’s Gray Treefrog (Hyla chrysoscelis). Their voices and, in some cases, their location, are the only way to distinguish the two without testing their DNA. I've never heard the singing of the Cope’s, which is distinct enough from that of H. versicolor to easily tell them apart, and only the latter not been documented in Rappahannock County, so I’ll stick to the Gray Treefrog here.
Only 1.5–2 inches long, the Gray Treefrog is well-adapted to escape notice. While it lives off the ground, away from terrestrial predators, its best protection is being able to change color to match its background. Its species name, versicolor, means changing color. It can change from brown or gray to blend into the bark of trunks and branches it perches on, or green to match foliage around it. A net-like pattern of dark lines further helps with blending into the frog’s surroundings. The only real contrast in color from normal background hues is a mostly hidden splash of bright yellow-orange on the underside of each hind leg. As a further hedge against predation, the Gray Treefrog calls mostly during times when light is dim—dawn, dusk, and heavily overcast days.
In Virginia, males of this species will start calling as early as March on warm days from near small, temporary (vernal) pools where they breed. But the breeding usually doesn’t get going until April, running through August. Some males can continue to call after that until they move to winter shelter.
I’ve managed to see Gray Treefrogs from time to time but never on a plant, where their camouflage works best. Such was the case in 2018, when our hollow received up to 100 inches of rain in some spots. That spring and summer, a couple of males were hanging out near my landlord’s Scanoe, a boat that wasn’t being used much at the time and collected water during the frequent rains. Checking the boat often after hearing males calling in the vicinity, I finally found and photographed one of them sitting on a piece of plywood under the boat’s seat, against a gray background. While his coloring blended in pretty well, his shape didn’t in this humman-made environment, so he was easy to spot.
With the male I heard singing near my deck this spring, I decided one day to try to find him after dark, using a flashlight. Frogs don’t recognize a flashlight beam as a threat and have a hard time seeing us at night, so that’s how I’ve managed to see a lot of frogs that readily disappear in the daylight, including the Gray Treefrog in the Scanoe.
That morning, a light rain was falling, and I decided it was a good time to pull some weeds in a tiny garden I’d planted this year with vegetables, herbs, and native wildflowers. I was down on my knees pulling weeds around my tomato plants. I was training the tomatoes to grow up string attached to a fan-shaped metal trellis that’s about four feet tall. When I looked up from pulling, I found a Gray Treefrog perched on a crossbar directly in front of me, just over a foot away.
The frog was totally still, which is this species’ normally does when not calling—to avoid predators and to ambush prey. His huge toes, specially designed to cling to pretty much any surface, were tightly wrapped around the thin bar, which is about a quarter inch in diameter. Around him was foliage from tomato plants, and in back of the plants was the gray foundation of the house. (See more about the toes and other cool facts for this species at the end of this post.)
The frog on the trellis was about 1.5 inches long. Although he wasn't singing, I could tell it was a male by his dark throat; females’ are white. I took a lot of photos, silently grumbling to myself about the poor light in these overcast conditions while trying not to get my camera too wet. But, true to this species’ nature, the little frog seemed to ignore me, not even moving its eyes as I moved around within inches of him to get the best angles.
I went back into the house for another camera battery, but he was right where I left him when I returned. I had found him around 6:30 and photographed him on and off over the next three hours. The earliest photos show the frog as mostly brown, with just a hint of green, but getting greener as the morning wore on.
With the rain increasing, I finally left the frog alone, knowing that if the sun did break through, he would likely seek a cooler, shadier spot, as treefrogs prefer. The sun finally did come out, the day heated up, and the frog disappeared.
Three wet mornings later, again under overcast skies, I was checking on the garden and found the treefrog was back, perched exactly where I’d seen him the first time. This time he was decidedly greener, blending in better with the expanding tomato foliage surrounding him. As before, he disappeared as the day heated up, but that evening I spotted him on the black garden hose coiled and hanging from a rack around the corner from the trellis. He had turned grayer, but he still stood out on the hose.
I had wondered what vernal pool he might be coveting and realized that it was probably the two large plastic buckets near the hose that I use to catch a little water off the roof. They were half full after the rain. They seemed a poor choice for a vernal breeding pool, but there was no other water nearby. (See a video of Gray Treefrogs mating on YouTube.)
I dug out a large garden tub, about 6 inches deep, that I use to mix soil. I placed a large rock in it to make getting in and out easier and to keep it from moving around and added a bit of water from one of the buckets. In 2018, a Gray Treefrog had laid eggs in a plant-pot saucer that was only about one inch deep, and I hoped a female would find this little makeshift pool adequate for laying hers.
The male kept disappearing and reappearing, eventually spending several days high up on the house, above the garden. The frog couldn't quite blend in with the minty green of the wall, but he scrunched up against the white corner board, diminishing his profile while benefiting from the shade the eaves on the board offered.
But the days kept warming. And the rain disappeared, along with the little frog. Although I occasionally heard a male calling in the evenings from various locations, none have appeared in my garden since early July. I imagine the metal trellis and black garden hose got pretty hot in the sun, so perhaps the frog decided to look for more comfortable digs. (See the slideshow below for more photos of this and other Gray Treefrogs.)
After a long dry spell, we’re now getting storms, usually accompanied by thunder and lightning, and some drenching downpours. No treefrogs calling yet, but I'm keeping my ears open, hoping to hear one under my bedroom window again.
© 2020 Pam Owen
Cool facts about Gray Treefrogs
Feet. According to scientists Robert C. Stebbins and Nathan W. Cohen in A Natural History of Amphibians, the individual toe-pad skin cells of the Gray Treefrog are flat and hexagonal, with a fluid layer that can excrete sufficient mucous when needed to create dynamic tension on dry surfaces. This adaptation enables the frog to cling to almost any surface, vertical or horizontal, including glass. (Think of those shower hooks that have plastic suction cups—wetting the cups slightly, then pressing them to the wall achieves the same effect.) Treefrogs have the added benefit of a small bone or cartilage that lies between the terminal toe bone “that supports the pad and its neighbor, giving great flexibility of the toe tip and reducing the angle of contact of the pad with the substrate beneath it, providing “a more effective grip,”
Voice. Since it doesn’t congregate with others of its kind at pools in great numbers as some anurans do, the male Gray Treefrog has evolved another tool to attract a mate—a surprisingly loud voice for its size. As Stebbins and Cohen note, it burns off a lot of calories in the process, more so than other cold-blooded vertebrates that have been documented. Since these frogs generally breed in ephemeral pools, mostly created through rain events, they tend to go quiet during dry weather.
The loud voice has another purpose, according to Animal Diversity Web: “The males aggressively defend and use their voice to outline their territories with extended calls. Satellite males, often in their first breeding season or otherwise disadvantaged, do not call to save energy. Instead, they lie in wait near a calling male and intercept the female by claiming the caller’s position after he moves away.” This species also has an “explosive bark” that can ward off predators, such as shrews, according to Stebbins and Cohen. But the male’s loud calls can also attract predators, so populations of this species tend to have more females (which don’t call) than males.
Location. As in real estate, an important factor in a male Gray Treefrog’s breeding success is location, location, location. The quality of a male’s territory may in fact be more important than his voice, Stebbins and Cohen point out. His perch site, near a suitable breeding pool, appears to be “critical” in attracting a mate.
Toleration of freezing temps. Some early-breeding frogs, including Wood Frogs and Spring Peepers, have antifreeze in their blood, enabling them to come out of hibernation in winter quickly to be the first frog species to breed in Virginia. Although the Gray Treefrog usually starts to breed a bit later, it also shares this adaptation. This tolerance for cold does enable it to hibernate at or near the ground surface—“under leaves, rocks, logs, or among tree roots,” according to Stebbins and Cohen.
Food. Adult Gray Treefrogs mostly prey on adult insects and their larvae, particularly those of butterflies, moths, and beetles. Mites, spiders, harvestmen, plant lice, and snails are also on their menu. Like most frogs, they are opportunistic and may also eat smaller frogs, including other treefrogs, according to Animal Diversity Web.