What do the frogs say: Frog mating season is here

Young bullfrog in duckweed - Photo by Kurt Schwenk

The University of Connecticut is in the midst of frog mating season, which is from early spring to July, Kurt Schwenk, ecology and evolutionary biology professor at UConn, said.

Their process of finding a mate involves the male frog calling, or croaking, at the breeding site to attract females, Schwenk said.

“The females get to choose which male frog they want to mate with and they primarily judge the quality of the male based on his call,” Schwenk said. “Sometimes frogs call to try and scare off a male competitor, and sometimes, if another male tries to mate with them, they make a special call called a 'release call', but virtually all the calling is related to reproduction.”

As the mating season progresses, the time that frogs begin to call gets later, Schwenk said. Most species call late at night, except for wood frog, which call during the day.

“Most calling happens at night, with a peak around 10 p.m. locally,” Schwenk said. “Most amphibians are nocturnal, meaning they are mostly active at night, and this is when nearly all the breeding occurs, as well as most other activity.”

Although one individual frog might not be too loud, a group of calling males, a large chorus, can be “absolutely deafening,” Schwenk said.

“I recently brought my herpetology class down to the Fenton River area at night, where we waded into a swamp in the midst of a huge chorus of spring peepers,” Schwenk said. “It's hard to describe what it's like. All I can say is that it is so loud, one stops hearing individual calls. It just becomes one loud noise that actually vibrates inside one's head! The sound is everywhere.”

Around UConn’s Storrs campus and the surrounding adjacent land, called the UConn Forest, there are eight species of frogs, in addition to seven species of salamanders, Schwenk said. This includes the pickerel frog and the gray tree frog.

Practically all types of frogs and salamanders must live in water, he said. During mating season, with the exception of red-backed salamanders and dusky salamanders, adult frogs and salamanders gather at ponds, wetlands or streams and mate.

“They deposit the fertilized eggs within the water so that the larvae can hatch out in the right place,” Schwenk said. “Nearly all amphibians simply lay the eggs and take off, leaving the embryos and larvae to fend for themselves.”

After mating, some frogs stay by the water while others go closer to land.

“Some frogs, like green frogs and bullfrogs, primarily remain around larger bodies of water, on the shore or in the water. Others, like wood frogs, head off into the woods once breeding is finished,” Schwenk said. “Frogs and salamanders can be encountered in surprising places, but with the exception of toads, they will always be someplace moist if not actually standing water.”

Although salamanders have similar mating habits as frogs, they do not call and have many differences to frogs, Schwenk said.

“Other than requiring standing water or at least, moist places to breed and live, frogs and salamanders are really quite different,” he said. “Although most people think of them almost interchangeably, they are actually not very closely related. They've been evolving as separate lineages since the earliest days of the first dinosaurs.”

Schwenk typically works with the feeding and chemosensory systems of lizards and snakes but has recently been studying the breathing habits of larval frogs, or tadpoles, he said.

“It is not well known that most tadpoles have functional lungs, despite living in the water and also having gills, as well as cutaneous respiration [which is] oxygen and carbon dioxide exchange through the skin,” he said. “Most people thought that the lungs only develop right before metamorphosis, [which is] when a tadpole changes into a terrestrial, adult frog, but we have found that they develop their lungs and start breathing air just 3 days after hatching from eggs.”

Schwenk said that he enjoys doing research with amphibians because of their unique and spectacular traits, such as the “explosive breeding choruses of frogs.”

“Frogs and salamanders are small, secretive and not usually an obvious part of the landscape, but when you start paying attention, they're an amazing part of our local wildlife,” he said.


Rachel Philipson is a campus correspondent for The Daily Campus. She can be reached via email at rachel.philipson@uconn.edu.