Amphibians of the Chesapeake Bay Watershed
Serenades from the woods
Bay Naturalist / By Kathy Reshetiloff - Bay Journal
There is an explosion of activity happening in tiny wetlands throughout the watershed. Species are gathering to attract their mates and breed. Most of us won't notice the event because of the players and their stage. The breeders are amphibians. Their places of pleasure are the tiny, often temporary, wetlands of our forests. Moist depressions, small ponds, and puddles, seeps, and small streams provide the essential element, water, which most amphibians need to breed.
The class of animals known as amphibians include salamanders, frogs, toads, and caecilians, worm-like animals with backbones. Amphibian comes from the Greek word “amphibios,” which means living a double life. The majority of amphibians are terrestrial as adults, but their larvae are aquatic. Most amphibians lay soft eggs in water. The eggs hatch to reveal a larval form. In the case of frogs and toads, the larvae are tadpoles, which depend on aquatic environments for survival. As the larvae grow, they experience radical physiological changes, a process known as metamorphosis, that transforms them into adults.
Forested wetlands are the main breeding sites. Because many forested wetlands are subject to periodic flooding from high ground water levels and heavy rains, temporary ponds form. These ponds may last from a few weeks to a few months and are critical to the life cycle of many amphibians. Forested wetlands contain a rich food supply of microscopic algae and a variety of invertebrates that contribute to the survival of amphibian larvae. Wetlands that are temporarily flooded often do not support predatory fish. These areas are safer for the development of eggs and larvae than permanently flooded areas or wetlands connected to waterways.
One of the most familiar amphibians in this region, yet the most difficult to actually see, is the spring peeper. On a warm night, wander near most forests and you will be serenaded by a chorus of these tiny frogs. The song, which sounds like the jingle of sleigh bells, signals an end to winter and the arrival of spring.
Most of the year, spring peepers live in the forest. Well-developed adhesive disks on their toes make peepers expert tree climbers. Peepers are brown, gray or olive. A dark cross, in the shape of an X, adorns their backs. These small frogs, often less than an inch long, can jump up to 28 inches, more than 20 times their body length!
From February to March, male peepers converge on their breeding grounds, singing to attract females. The mating call, a high-pitched ascending whistle, can often be heard up to a half a mile away. Males will often sing in duets, trios, or quartets.
Frogs and toads produce their peeps, clicks and croaks by moving air back and forth over their vocal cords. Like many frogs and toads, the spring peeper has a vocal sac on the throat that resonates the call. The male inflates its vocal sacs and as it calls, the inflated sacs resonate the sound. Peeping reaches a crescendo on the warmest night but ceases if temperature drops below 30 degrees Fahrenheit. When ready to mate, females arrive and choose their mates.
Often, males are so preoccupied with breeding that they will accidentally grab another male. A release call tells the offending suitor that he has the wrong partner. Frogs also vibrate their bodies to shake off mistaken males.
Mating occurs in shallow pools. The male sits on the female's back and fertilizes the 800-1,300 eggs as she deposits them. The eggs, only a fraction of an inch long, are laid singly on underwater vegetation. Depositing eggs can take up to one day to complete. Once breeding is finished, peepers return to the trees.
After two or three weeks, eggs hatch and tadpoles, less than 1/5 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 blue-green algae.
After five months, tadpoles metamorphose into adults. Gills are replaced with lungs, legs grow, and tails are absorbed into the body. Since adult frogs are carnivores, a 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 new woodland home, continuing to grow and mature. Spring peepers reach sexual maturity in 3 to 4 years.
Late winter and early spring rains and thawing snow contribute to the creation of open water areas that are breeding grounds for amphibians like the spotted salamander, wood frog, and American toad. Since the water in these areas is not permanent, the breeding season for these species may only last a few weeks. The larvae must develop quickly. Permanent water sources provide habitat for bullfrogs and carpenter frogs. Small, shallow streams serve as breeding grounds for the carpenter frog and a variety of salamanders. The marbled salamander, however, takes a different approach to breeding. During late summer the female lays her eggs at the bottom of dry ponds or in low depressions. The eggs will not hatch until rain covers them.
All across the country, there has been a drastic decline in amphibian populations. Scientists believe that degradation or loss of critical forested wetland habitat to be the main cause. Many amphibians breed in the same ponds and wetlands in which they were born. If these natal areas are disturbed or lost, those individuals may not breed. Deforestation results in a loss of upland forest habitat used by adults and dispersing juveniles. Fragmentation of habitat is also a problem. As wooded tracts shrink in size, the remaining amphibians become isolated and inbreeding may occur, weakening the species.
Protecting upland and wetland forests, particularly those adjacent to each other, is the first step toward preserving amphibian populations. Vegetated buffer strips along waterways are equally important to the survival of amphibian populations. Rivers and their flood plains provide excellent corridors that connect isolated or fragmented woodlands. These corridors are especially important in highly developed areas like the mid-Atlantic states. They allow amphibians to move between small pockets of existing forests and wetlands, helping to ensure healthy and diverse populations.
Amphibians are not the only ones to benefit from preserving woodlands and forested wetlands. These same areas are also habitat for a multitude of invertebrates, fish, birds, and mammals. By preserving woodlands, wetlands, and river corridors, we also reduce the amount of nutrient and sediment runoff entering rivers and the Bay. In addition to the ecological values provided by forests and their associated wetlands, these areas have important commercial, social and aesthetic values. These are excellent areas for hunting, fishing, hiking, camping and birdwatching. In this increasingly developed landscape, we often need a place to which we can retreat. Forests and their wetlands offer us an alternative to our concrete world, a place where we can be serenaded by a chorus of frogs.
Kathryn Reshetiloff is with the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office in Annapolis.
Serenades from the woods
Article from Bay Journal - March 1994