Frogs are the birds of the night.

Henry David Thoreau

There is something magical about the sounds of frogs and toads. In my museum days, I used to do a workshop activity where participants got a call sheet for a local frog or toad species. Each sheet had a photo and a description of the amphibians’ song. Teams imitated their call and then we would listen to a recording, and each group would try to identify their species’ real call. People always loved imitating the sounds and hearing the recordings, but few could match the quality of the actual amphibian voice.

Part of the reason may be the special adaptations that frogs and toads have for communicating with one another. The most visible asset is their vocal sac.

Upland Chorus Frog calling (click photos to enlarge)

The vocal sac is an elastic membrane originating from the floor of the mouth of most male frogs. It tends to be thinner on many of the smaller frog and toad species that call in air, and more thick-walled on the larger species, like Green Frogs and Bullfrogs, that call in water. Vocal sacs come in a variety of shapes and sizes, and can be single or paired. To initiate a call, a frog inflates its lungs, and closes its mouth and nostrils. Air is then forced out of the lungs through the larynx and into the vocal sac, which then enlarges. To create the series of sounds typically categorized as the advertisement or mating calls, the air is passed back and forth from the vocal sac to the lungs without being expelled. While it appears that the vocal sac helps to radiate and amplify the sound, studies have shown that other body parts, especially the “ears”, or tympanic membranes, also play an important role in amplifying the call notes of certain species.

When seen from behind, as in the short video clip below, it is clear that this sound-producing activity must be a lot of work for a male frog.

Some scientists also speculate that the act of calling is both the most energy-draining and predation-risky behavior that a male frog or toad exhibits. But, aren’t we glad they do? It is a fascinating behavior to observe, and the sounds produced are a wonderful addition to our natural sound-scape. I imagine the female frogs and toads appreciate it as well.

Below are a few photos I have taken over recent years of frogs and toads calling in a variety of habitats in North Carolina. I look forward to adding photos of more species in the coming months.

The Pickerel Frog has paired lateral vocal sacs that produce a low-pitched call sounding like a human snore.

Pickerel Frog

One of our earliest frog songsters, the Spring Peeper repeats his high-pitched note about once every second. One reference stated that researchers estimate a male Peeper may repeat his call up to 4,500 times in a single night.

Spring Peeper

The harsh trills of the Cope’s Gray Treefrog can be heard in many North Carolina forests and neighborhoods throughout much of the summer.

Cope’s Gray Treefrog

Considered by many to be our most beautiful frog, the Pine Barrens Treefrog is found primarily in the Sandhills. It became the Official State Frog in North Carolina in June, 2013.

Pine Barrens Treefrog

Fowler’s Toads are abundant in the Piedmont. Their nasal call (“waaaaah”) can be heard from about April through July.

Fowler’s Toad

A chorus of trilling American Toads always reminds me of what a group of distant alien space ships might sound like in early sci-fi films.

American Toad

Thoreau (no surprise here) had a more eloquent take on the sound of the American Toad…

Close by, it is an unmusical monotonous deafening sound, a steady blast (not a peep nor a croak – but a kind of piping). But far away, it is a dreamy, lulling sound, and fills well the crevices of nature.

American Toad reflection

Thoreau also had some intriguing insights on how we may share some similarities with the amphibians singing in our neighborhood wetlands…

I see the relation to the frogs in the throat of many a man. The full throat has relation to the distended paunch.

Not sure where ol’ Henry was going with that one, but this final thought seems clear enough…

The music of all creatures has to do with their loves, even of toads and frogs. Is it not the same with man?

Cope’s Gray Treefrog vocal sac backlit