It was 5 p.m. Feb. 27 and unseasonably warm when I decided to stop at a local park on my way home, anticipating the signal that spring has arrived. The park is really a sports complex, several acres of sterile, barren ball fields. But around the edge is a patchwork of woodlands, streams and meadows. Recent rain had saturated the ground and I was hoping that enough water had filled slight depressions on the landscape to create temporary shallow pools.
As soon as I got out of the car I heard what I was hoping for. Although they were probably a half-mile away, spring peepers, a tiny species of frog, had left the trees to converge upon one of these pools, singing or rather "peeping" to attract a mate and breed.
I couldn't see the pool but followed the sound. The peeping reached an almost jingle bell tone as I closed in on the tiny tea-colored pond. I couldn't see them, but did occasionally pick out an individual's song among the chorus. Did this frog's voice stand out and attract a mate that night or was it better to be in tune with the rest of the crowd?
Throughout the Northeast, temporary pools, known as vernal pools, are coming to life as spring peepers and other frogs, toads and salamanders converge on them to breed. The pools form as shallow depressions in forests, flood plains and meadows fill with water from rain, snowmelt and high water tables.
Because vernal pools are not directly connected to flowing water sources, they do not support fish that would prey upon amphibian eggs and larvae, making them a secure place for these animals to reproduce.
Most of the year, spring peepers live in the forest. Adhesive disks on their toes make them expert tree climbers. Peepers are brown, grey or olive and sport a dark "X" on their backs. These small frogs, only 0.75– to 1.50 inches in length, can jump up to 28 inches, more than 20 times their body length!
During their breeding period, from February to March, spring peepers leave the trees to mate in open water. Spring peeper breeding follows the wood frog by a week or two. But the unmistakable mating call and large geographic range makes the spring peeper one of the most familiar frogs in North America. Spring peepers can be found from Manitoba to the Maritime Provinces in Canada, south through central Florida and west to Texas.
Frogs produce their calls by moving air back and forth, passing it over the vocal cords, which causes them to vibrate and produce sounds. Peepers also have vocal sacs that resonate their calls. These are stretchy sacs near the frog's throat. The male inflates its vocal sacs by pushing air through slits in the floor of its mouth. Peeping reaches a crescendo on the warmest nights and almost ceases if temperatures drop below 30 degrees Fahrenheit.
When they are ready, the females arrive and choose their mates. Mating occurs in shallow pools. The male sits on the female's back and fertilizes the 800–1,300 eggs she deposits. The eggs, only 1/200th of an inch long, are laid singly on underwater vegetation. Depositing eggs can take about one day to accomplish. Once breeding is completed, peepers return to trees. The cycle begins again the next spring.
After two or three weeks, eggs hatch and tadpoles, less than 0.2 of an inch in length, emerge. They spend most of their time eating and growing. Tadpoles are herbivores. They feed by inhaling water and filtering out blue-green algae. One ounce of tadpoles can clean 12 gallons of water every day.
In five months, tadpoles metamorphose into adults. Gills are replaced with lungs, legs grow, and tails are reabsorbed into the body. Adult frogs are carnivores, so the tadpole's intestines shrink and the mouth becomes larger to adapt to eating and digesting animal material. The new tiny frogs leave the water for their woodland habitat, continuing to grow and mature. Spring peepers reach sexual maturity in three to four years.
Because spring peepers and other amphibians require such unique habitat conditions to breed, they are very vulnerable to land use changes. Many amphibians return to the same ponds and wetlands in which they were born to breed. If these natal areas are drained or filled, those amphibians will not breed.
These animals need both an aquatic environment to reproduce and develop and a terrestrial environment the rest of the time, so the loss of the woodlands surrounding their seasonal pool can also be devastating. As wooded tracts shrink in size, an amphibian population can become isolated and inbreeding may occur, weakening the species.
Why should we care? Amphibians help us to measure the health of the environment. Amphibians exchange water and air primarily through their skin. In addition, they can absorb pollutants that are in the soil and water. A decline in a local amphibian population may be an indicator of a contaminant problem.
Amphibians possess many foul-tasting chemicals in their skin and glands to protect them from predators. Some of these chemicals have medicinal value. Some companies try to replicate these compounds for heart medications, organ glues and pain killers.
Aesthetically, many amphibians are extremely beautiful creatures that we should all have the opportunity to observe and enjoy.
Protecting forested wetlands and woodlands is a first step to preserving amphibians. Adults require wooded tracts but need access to shallow aquatic habitats to breed. Vegetated buffer strips along waterways are equally important. Rivers and flood plains provide excellent corridors to connect isolated woodlands. Amphibians use these corridors to move between small pockets of existing woodlands and wetlands, helping to ensure healthy and diverse populations.
These same areas are also habitat for other wildlife including invertebrates, fish, birds and mammals.
Protecting woodlands, wetlands and river corridors also reduces the amount of nutrients and sediment entering rivers and the Bay.
And, in this increasingly concrete world, we can all use a natural place to escape to, no matter how small. These springtime pools offer a retreat to enjoy the serenades from the woods.