I mark the progress of spring by the succession of frogs that raise their voices to court and reproduce. My favorite, gray treefrogs, pipe up in late May, long after the wood frogs, peepers, and American toads have had their say. With this spring being particularly cold, treefrogs are only now reaching their peak.
On warm, humid June nights, I listen for the males trilling from the saplings and reeds of a marsh near my home in Thetford. The treefrog song is harsher and shorter than that of the toad, lasting only five seconds or so compared with the toad’s 30 seconds or more. Gray treefrogs are much larger than spring peepers, and their inner thighs are bright orange. The color of their warty backs – etched with irregular black lines – can change from gray-brown to light green to pearly gray depending on the season and the habitat. I’ve caught gray-brown males along the edge of open water where they blend into the mud. Those trilling from the trees are gray-green. Late in June, when I catch treefrogs in my flashlight beam high in the aspens, where they forage for insects, they are a bright green – the color of young leaves, which I assume camouflages them from foraging jays and crows.
I’ve heard a treefrog as early as May 6, which is extremely early, calling from the saplings behind the baseball field at Thetford Academy. As the month grows warmer and more humid, they follow moisture downhill and collect in the alders and aspens that flank the marsh near my home. When the treefrogs are calling, the chorus can be deafening. Early one June, I went into the marsh with hip waders and a headlamp looking for frogs. Three males trilled from a tangle of alder – a counterpoint to the peepers that still chorused in the background. Finding the treefrogs was a challenge. As I hacked my way closer to the songs, the frogs stopped. So I eased away from the brittle vegetation and into the shallows. Although the frogs resumed their chorus, I had made a bad choice. Five feet from the reeds, I stepped into a soft spot and settled up to my waist in ooze.
By mid-June, finding gray treefrogs is much easier. Around our local marsh, the chorus has swelled to 20 or so males, and the breeding season is at its peak. The nights are warm and, caught in their frenetic courtship, the treefrogs pay little attention as I wander the shoreline.
Once while wandering I found a male in a spit of cattails. Each time he trilled, he filled his vocal sac with air, lifted his head toward the sky, and vibrated his entire upper torso. After each trill he lowered his head and waited. Whenever a neighboring frog sang, he started up again. After more than an hour of discordant music, a large gray female treefrog hopped over and stood on the male’s back, choosing him over the six frogs in the adjoining chorus. The male moved out from under her, climbed onto her back, and locked into amplexus, the frog’s mating embrace. Eventually the frogs piggybacked into the shallows. Almost as soon as they were gone, another male hopped over and began calling from the exact spot the first male had left, as if that cattail spit had been blessed.
Last week I began visiting the marsh after sundown, just before darkness settled into the valley. No treefrogs were yet in the water – they were calling from the aspens, alders, and red oaks 30 or 40 yards from the shoreline. As night congealed, the treefrogs moved ever closer to the shore, jumping from tree trunk to tree trunk as though playing follow the leader. When one treefrog left one perch for another closer to the open water, the next frog moved up from the back to take his place. The wave of several dozen frogs continued until the last one had made it all the way to the water to secure a calling site – and continue the annual amphibian chorus well into the summer.