Have you ever heard them? They're LOUD! In the event you haven't, go have a listen: Peepers
As to HOW they "sing" they have vocal pouches that vary in size and stretch like balloons. These sacs serve as a resonating chamber, allowing the frogs to SING!
Male frogs vocalize by squeezing their lungs with their nostrils and mouth shut. Air flows over their vocal chords and into their vocal sacs blowing it up like a bubble gum balloon. This increases the volume of the sound, reaching out to female "ears." There's a great searchable website called "All About Frogs" that has tons of information: All About Frogs
One day long years ago, when we were living across the road in the old farmhouse, I took a walk down to one of our ponds to see if I could catch a peeper. No small feat, believe me!
I wondered at their size....or, maybe more to the point, just how many there were! The chorus was ear-splitting close up and shrill. There must have been hundreds, maybe even thousands ringing that pond. Their blended voices are an eternal feature of summer. I know you've all heard the sound, at least in movies as background outdoor noise.
Searching for one in "real time" I got down on hands and knees, stealthy as all get out, and sneaked (I like the word "snuck" better, but it's still listed as "improper usage"...but "snuck up" seems to nail it) up on the sound. Even with all my soft stepping, they still heard me and all went silent for a moment. But I held my ground and my breath and waited. Soon, they started up again, and I set out determined to snag one. As I got closer and closer the peeping stopped again. I froze. I was halfway to that grass clump where the piercing sound was coming from and nary a peep. I waited and waited. Finally, one timid peep; then another. I zeroed in on the sound coming from the clump. Patiently, I waited, and before long the entire chorus was in full throat once more. I exhaled. Sneak. Sneak. Sneak....hold still.....POUNCE! And I got him!
Slowly, I opened my hand, just enough to see him. without losing him. I could not believe how tiny he was! About 3/4 of an inch and smaller than the tip of my little finger! All that noise coming from this little creature?
From a museum in Nova Scotia, here's a broad description of their emergence:
"These thumbnail-sized tree frogs leave their woodland hibernation sites as early as late February or early March. Perched on grasses and sedges at the edge of ponds or roadside ditches, the males call mates with a shrill "peep peep peep". Their brown or gray colour, always with a dark stripe on the sides of the head and dark markings on the back provide excellent camouflage against the dead spring grasses. If the night is cold, Peepers retreat under leaves and stems. You'll likely hear hundreds before you ever see one."
And I can personally vouch for that last fact. They're a noisy bunch! And they're awake! I only hope last night's cruel temperature plunge hasn't discouraged them. It's supposed to warm up today. Welcome back, Peepers!