Louisiana's State Amphibian: The Green Treefrog, Hyla cinerea

Monday, July 26, 2010

Nature Notes
by Bob Thomas

Green treefrogs (Hyla cinerea) are one of Louisiana's most recognizable frogs. They are common denizens of ponds, roadside ditches, canals, and swamps, often found on doors and windows where they feed on insects drawn by the porch light.

Green treefrogs are appropriately named. They have lime-green backs (often with yellow or golden spots) and pale bellies, separated by a heavy white lateral line that typically stops before it reaches the hind legs. This species has the ability to vary its color. When cool and inactive, a specimen may be olive drab to brown or gray; when warm and active, the same animal will be a beautiful shade of lime green.

In Louisiana, green treefrogs are usually inactive during the cooler months. They begin to move about with the warming weather and begin breeding in late spring, an activity they continue as late as August. A gravid female may contain as many as 700 eggs, but she usually deposits them at the surface of pools in clutches of up to 40 eggs each. The norm is for a female to develop one complement of eggs per season, but there have been rare records of green treefrog females doing so three times in one season. In any case, the eggs hatch after two days and the tadpoles metamorphose into froglets in about two months. Those little frogs will be ready to breed by the following spring.

One of the common names for this species is the Bell Frog. This name comes from the mating call for the species which sounds like a ringing bell: quonk, quonk, quonk. When calling in a chorus of individuals, they frequently harmonize and the call seems to be quonk-quack, quonk-quack, quonk-quack. To make matters more interesting, each male varies its call depending on circumstances. Females rarely vocalize. Studies have shown that green treefrogs tend to use a territorial call at dusk. This call tells other males to keep their distance. Following this, the frogs slowly move toward the breeding pool. During this time, they use an encounter call which is rather antagonistic if they accidently bump into other males. When they reach the pool, they switch to their courtship (mating) call that is intended to attract the females for breeding. This call is the most familiar to local citizens, and research has shown that female green treefrogs can hear the call 300 yards away.

For most frogs, the mating pattern is for each adult male to sit and croak until a female is attracted. Our little critter, however, has an additional behavior. It is not unusual for one or more noncalling males to crouch silently near a calling male. Since they are scattered around the calling male, they are termed satellite males. Their purpose in the grand scheme of things typifies how Mother Nature works. Croaking all night to attract a mate consumes a lot of energy. Somewhere along the line, green treefrog males discovered that, if they simply crouch down and wait, the calling male will eventually either tire out and leave its prime territory, or it will be successful and its new female friend will hop away toward the breeding pond with him holding on for dear life. When this happens, one of the satellite males will assume the role of Excellent Croaker. Yet another way satellite males might save energy is by grabbing a female that is moving toward the dominant calling fellow who has expended all the energy. Even frogs don't always want to work for their pleasures.

Green treefrogs eat just about anything they can get into their mouths. This usually includes insects, spiders, and the like. They seem to be an important part of the food chain, because they are eaten by many critters such as snakes, birds, turtles, fish, and mammals like raccoons and otters.

The facts that green treefrogs are so abundant and distributed throughout Louisiana makes them an excellent choice as the state amphibian (assuming the legislature should expend its time with such designations).

Also published in Nature Profile, The Times Picayune, May 27, 1982.
Also published in Delta Journal, The Times Picayune, May 24, 1989.

                                      

Louisiana's state amphibian, the green                                 Mating pair of green treefrogs.
treefrog, Hyla cinerea.                                                        Photo by Bob Thomas.
Photo by James Beck.

                              

A calling male green treefrog.                                             A mushroom makes a nice perch for a
Photographer unknown.                                                  
green treefrog in Big Thicket National
                                                                                        Preserve, Texas.
                                                                                          Photo by Bob Thomas.

                              

Green treefrog foraging on the base                                Typical view for many people of a green
of a tupelo gum tree in Jean Lafitte                                  treefrog feeding near lights on the front
Nature Park.                                                                  porch.
Photo by Bob Thomas.                                                 Photo by Bob Thomas.