Throughout the Chesapeake Bay watershed, winter thaws and spring rains are creating temporary pools in woodlands, wetlands and meadows. These seasonal pools, while often small and inconspicuous, are coming alive as frogs, toads, salamanders and other amphibians converge on them to breed.
Seasonal pools have four distinct features: surface water isolation, periodic drying, small size and shallow depth, and they support of a unique biological community. Seasonal pools experience regular drying that excludes fish and are critical breeding habitat for amphibians in the mid-Atlantic region.
The Greek word "amphibios" literally means creatures with a double life. Amphibians spend part of their lives in water and part on land. Most amphibians lay soft eggs in water. The eggs hatch into an aquatic larval stage that looks and acts quite differently from the more terrestrial adult stage. For instance, toads and frogs eggs hatch into tadpoles, which can only survive in water. As the larvae grow they experience radical physiological changes, a process known as metamorphosis, which transforms them into adults.
Some salamanders, like the marbled salamander (Amystoma opacum), actually begin their breeding cycle in fall, migrating to pools and depositing eggs. The larvae overwinter in the pool. Other salamanders, like the spotted salamander (Amystoma maculatum), wait until spring to visit pools and lay their eggs. Many salamanders return to their birth pool to breed.
Unlike quiet salamanders, toads and frogs converge on vernal pools and call to attract mates. Frogs produce their calls by moving air back and forth over their vocal cords, making them vibrate to produce sounds. Although you may not see them, you can identify what species are breeding by listening to their calls.
Wood frogs (Rana sylvatica) migrate to vernal pools early in the spring, often before snow and ice have completely melted. The call of the wood frog is a hoarse clacking sound, reminiscent of a quack. The wood frog is an explosive breeder, usually laying a large mass of eggs in a few days and leaving soon after.
The spring peeper (Hyla crucifer), a tree frog, follows the wood frog by a week or two. From February to March, spring peepers leave their trees to mate in open water. Its unmistakable mating call, the peep, and large geographic range makes the spring peeper one of the most familiar frogs in North America. The mating call can sometimes be heard up to half a mile away.
Another familiar amphibian is the American toad (Bufo americanus). Its habitat ranges from mountain wilderness to suburban backyards. One is likely to find the American toad almost anywhere, as long as there are moist places, plenty of insects to eat and shallow waters, where they breed from March to July. Despite their warty appearance, their mating call is a pleasant musical trill.
Around the world, amphibian populations are declining with the loss of seasonal pools to development. In the mid-Atlantic region, 26 percent of all state-listed threatened and endangered amphibians are dependent on seasonal pools.
Many amphibians return to the same ponds and wetlands where they were born to breed. If natal areas are disturbed or lost, those amphibians will not breed. Deforestation reduces woodlands needed by adults. Fragmentation is also a problem. As wooded tracts shrink in size, the remaining amphibians 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 and thus can absorb pollutants that are in the soil and water. Like a canary in a coal mine, a decline in local populations may indicate a contaminant problem.
Amphibians contain many foul-tasting chemicals in their skin and glands that protect them from predators. Some of these chemicals have medicinal value. Drug companies are looking to replicate some of 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 toward preserving amphibians. Rivers and floodplains provide excellent corridors to connect isolated woodlands. Amphibians use these corridors to move between woodlands and wetlands.
We all benefit from such actions. These same areas are also habitat for a multitude of 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.
You can help scientists monitor amphibians in your area by volunteering in one of these programs:
- North American Amphibian Monitoring Program, Patuxent Wildlife Research Center www.pwrc.usgs.gov/naamp/.
- Frogwatch USA, National Wildlife Federation, www.nwf.org/frogwatchUSA/.
Footnote: In the evening, as I head home, I encounter one of the most delightful sounds of spring. I drive past small forest. Within this forest is a little wetland spot, a seasonal pond that you can't see but can hear. I slow down, turn off my radio and roll down the window. And for an instant, I am serenaded to an almost deafening song of spring peepers.
There is also a For Sale sign nearby. If the woods are developed, the pond where these very vocal frogs visit each year to mate will likely disappear. And so will that song.