|The Question: I work at a home office in a housing development situated in hilly northern New Jersey. It’s near a group of small ponds – which I think are natural ones – surrounded by a perimeter of patchy woodland. There are places where people’s back yards go right down to the water, and walking paths nearby. So the human element is right there, but it’s quiet enough so wildfowl use the ponds in transit in spring and fall, deer stop by, and at least one great blue heron takes up residence.
In June and July when I walk near the water at midday, I often hear an alarm call that sounds like a single high squeak or chirp, and hear a small splash as something dives into the shallows. What do you think it might be? (Not a loud enough plop to be a bullfrog, which are definitely present.)
Submitted by: Mary Ellen, northern New Jersey
The Short Answer: I’m pretty sure that what you’re hearing is the alarm call of either a Green frog (Rana clamitans) or a Bullfrog (Rana catesbeiana). Juveniles, especially, will make a squeak or chirp as they jump into the water. I tried and tried to find a recording of the alarm chirp of a green frog without success. (If anyone knows where I can find one, please let me know.) However, I did find a recording of the alarm call of a Bullfrog. Go to http://www.californiaherps.com/frogs/pages/r.catesbeiana.sounds.html. About the middle of the page, you’ll find a recording of alarm calls. My recollection is that the alarm call of a green frog is similar, but I wish I could verify that. Maybe you could record your chirps next spring and send me a file.
More Information: Green frogs and Bullfrogs are closely related and fairly similar at first glance when they are sitting in the water. The largest Bullfrogs are definitely larger, 6-7 inches (15-18 cm) not counting the legs, than the largest Green frogs at 4-5 inches (10-13 cm). Both are predominantly green in color, but can be various shades of green and brown. One simple way to tell them apart is that the Green frog has two prominent ridges that begin behind the eyes and run the length of the body. These “dorsolateral ridges” are absent on the Bullfrog.
The Green Frog’s mating call is a loud, twangy single note bark. The Bullfrog’s is a deeper sometimes two-noted thrum. You can hear the difference at this site: (Bullfrog #1, Green frog #8) http://www.nbii.gov/portal/server.pt/community/amphibian_monitoring/1527/east_tennessee_frog_calls/5318. You can also hear and see the difference between the two at these two Youtube videos. In the Green Frog video, note the prominent dorsolateral ridge.
Impress Your Friends: It’s easy to tell males from females in both the Green frog and the Bullfrog. Males have a yellow throat, and the tympanum, the visible round external eardrum located behind the eye, is much larger than the eye. Females lack the yellow throat and the tympanum is about the same size as the eye. In the pictures above, the Green frog is a female and the Bullfrog is a male.