Listen now for the frogs
Diary entry for March 29, 2021: “Drove to Farmer’s Valley and stopped several times, hoping to hear wood frogs.”
Although the temperatures have been low at night, our days are sunny, and I thought perhaps the wood frogs might have begun their mating rituals.
The wood frog’s breeding season is in early spring, even before that of the well-known spring peepers. Often, the wood frog’s breeding season begins while patches of snow are still on the ground and the water’s edge is still frozen. The wood frog migrates to water to breed. Most of these water breeding sites are low areas in the woods that have filled with water from the spring runoff.
Since these water areas are short-lived the wood frogs’ breeding season has to be early and quick. Occasionally, in a cold snap, both the adults and eggs will freeze. According to the Pennsylvania Fish and Boat Commission’s book entitled “Pennsylvania Amphibians and Reptiles” the eggs do not die but simply lie dormant, while awaiting warmer temperatures to develop.
The wood frog is a diurnal amphibian, meaning the frog is primarily active during the day. However, the wood frog, with its secretive and solitary manner, has the ability to blend in with the background, making it almost impossible to observe. The exception to this is during the breeding season.
Male wood frogs seem to arrive at the breeding ponds at the same time. A warm rain and temperature reaching 50 degrees are usually needed to entice the wood frog from hibernation. This sometimes occurs in late February, however, in Bradford County, it is usually not until the middle of or late March when I hear the male wood frogs calling.
While floating on the surface of water, the male begins to make a series of short, raspy duck-like calls. A single call alone is not very loud but the chorus of hundreds of frogs can be heard a long way off.
Usually, the females are attracted to the water a day or two after the males begin calling. Once a female enters the water, the males dash to her and a slight scuffle occurs. The winning male grasps the female around the body with his forelegs (a position referred to as amplexus), and then, both swim to an egg laying site, which is usually in a sunny area. After the female deposits two to three thousand eggs into the water, the male will fertilize the eggs.
The egg cases, which are black and encased in a clear jelly mass, attach themselves to the growing green vegetation. The black of the egg collects the sun’s heat, while the jelly coating helps to insulate the egg. Heat is also generated by a normal metabolic process, which increases the temperature of the embryo.
Occasionally, there are communal egg-laying sites in which females deposit eggs on to other female’s egg masses. Sites have been documented where several females laid their eggs in one large mass. When this occurs the eggs on the inside of the egg mass are about six degrees warmer than eggs on the outside of the egg mass.
After the egg masses are in the water for about a week, they begin to flatten; float upward to the surface and spread out, appearing to be green scum on the surface of the water. From this point, the tiny eggs take less than a month to hatch. The tadpoles leaving the eggs are a greenish olive in color, with a high tail crest. They remain as tadpoles for approximately two months.
After breeding occurs, the adult frogs depart the breeding area as quickly as they arrived. The wood frog’s breeding season seldom lasts for more than a 10-day period. They will spend the summer far away from the water. The wood frog is found throughout Pennsylvania and is the only frog residing in the frosty environment found north of the Arctic Circle. Since the wood frogs favorite haunt is shade and moisture, woodlands are a likely area to find them. As winter settles over its forest home, the wood frog burrows beneath the forest debris to hibernate under the leaves or beneath moss-covered logs.
The typical amphibian’s life begins in the water, and since each egg has a small yolk, the embryo has to hatch within a short time.
The tadpole has to change drastically as it grows. The external gills are soon lost, and within a few weeks, tiny hind limbs appear, followed by forelimbs. As the frog tadpole grows, the tail diminishes until the little creature has finally changed completely to its adult form. An important internal change has also taken place in the digestive system. Tadpoles (plant-eaters) and adult amphibians (flesh eaters) have completely different types of digestive systems.
Frogs never die of old age since they have many enemies, such as herons, turtles, snakes, larger frogs, fish and of course, man. Our population of frogs has been on the decline but not because of predators. The decline is because amphibians have very small lungs, and part of their breathing is through the skin. The skin cannot prevent the entry of the many chemicals, which are used today in agriculture, that are usually lethal to amphibians.
Our word frog comes from Old English frogga, which was probably said as a playful alternative to the more serious frosc, which was used as a derogatory word for a French person. The word goes back to the 18th century and was presumably inspired by the French appetite for frog legs. Frogs and toads make up an order known as Anura, which means without tails.
Frogs are amphibians. Our word amphibian comes from two Greek words: amphi, meaning on both sides and bios, meaning life. Translated as “living in two places,” referring to the amphibians dividing their lives between land and water.
When the breeding season for the wood frog is almost over, the breeding season for the spring peepers will begin. There could be a time period when both the wood frogs and the spring peepers are heard calling, a sound similar to sleigh bells.
Bill Bower is a retired Pennsylvania Game Commission Wildlife Officer. Read his blog and listen to his podcasts on the outdoors at www.onemaningreen.com.