Life at a Vernal Pond

It was not the year to observe our vernal ponds. But how was I to know that? After two years of more precipitation than usual, all the depressions on top of Sapsucker Ridge beneath the oak and black cherry forest had filled with water.

In late March, I counted four ponds. Three of them were clustered near each other. First were two old small ponds that had merged and formed a larger, figure-eight-shaped pond 30 feet long and eight feet wide. This pond was closely followed by a second small pond that was barely six feet in diameter. The last of the cluster, once a small pond, had become the largest of all–40 feet in diameter.

The fourth pond, farther along the ridge, had been the only reliable one over the years and had supported, until a couple dry years, a population of breeding wood frogs. That pond, though, now completely hemmed in by fallen debris from the ice storm, had become the second largest pond at 60 feet long by 15 feet wide.

Vernal ponds, also called “depression ponds,” “temporary ponds,” or “vernal pools,” are ponds of water that are mostly less than 120 feet wide and four feet deep and are created by snow melt and spring rains. Often these ponds dry up in mid-to-late summer or early autumn, which prevents permanent residency by fish. Without such predators, the larvae of some salamander and frog species can thrive.

Once the ice had melted from our ponds, I spent many hours watching not only the activity in them but the wildlife around their perimeters. On the last day of March, as I sat near the largest pond, I heard a rustle in the leaves nearby. Hen turkeys waded through the far end of the pond. A few looked over at me, but I didn’t move. They continued filing past, and altogether I counted 17. On the rise above the pond, and following well behind like an outcast, a tom turkey, sporting a medium-sized beard, silently fanned his tail while keeping a respectable distance. The hens foraged as they moved off through the forest and never seemed to notice him.

On April Fool’s Day, I heard the quacking calls of wood frogs from the oldest pond. I crept up quietly to glimpse them calling and swimming, but I wanted a better view of the action. I crossed to the other side of the pond and the frogs dove to the bottom. Making myself an elevated seat atop two fallen cherry trees wedged against a live chestnut oak, I sat motionless for half an hour, but the male frogs didn’t call. A few froggy heads did appear above the water and fixed their unblinking eyes on me.

Although the frogs provided little entertainment, other creatures did. A pileated woodpecker’s maniacal cry outdid the “pee-wee” song of a black-capped chickadee and calling golden-crowned kinglets and an eastern phoebe made themselves heard above the roar of Interstate 99 traffic at the base of the ridge. The next several days winter returned for what we hoped was its final blast. Terrific winds, cold, rain, and snow sent the wood frogs down into the pond muck, and on the fourth of April, a skim of snow still encircled the vernal ponds while a mica-thin, translucent layer of ice covered the larger ponds. Golden-crowned kinglets and black-capped chickadees foraged around the oldest pond as I sat there. Tufted titmice and a singing winter wren poked around in the tangled mass of ice-felled trees, and live trees creaked and groaned in the blessed wind that drowned out the traffic din below.

A cap of white crowned all the mountains, but the valleys were brown. A hairy woodpecker called, and I heard a singing golden-crowned kinglet. Then kinglets and chickadees landed and foraged on a witch hazel sapling three feet from my head, the kinglets fluttering down around me like animated butterflies. A chickadee bathed in a strip of open water near the edge of the pond. Once I heard a singing brown creeper, and then I watched one hitching its jerky way up a series of nearby tree trunks even as sodden snow plopped down from the tree branches.

Two days later, it was warm again. The largest vernal pond also held about 10 calling, swimming wood frogs, while the oldest pond contained 20 or more and four wood frog egg masses.

By the tenth of April, even the two smallest vernal ponds held large clumps of wood frog egg masses. But all the ponds were shrinking in the spring warmth, and on April 12, I was shocked to find the oldest pond dried up. Only four large gelatinous blobs containing both wood frog eggs and tiny, just-hatched black tadpoles lay in the mud.

The two small ponds had some water, but their egg masses were gone. Turkey droppings around the ponds’ edges made me suspect that turkeys had made a meal of the eggs.

The largest pond still held plenty of water, although it too was retracting. Several egg masses bobbed in its two-foot-deep middle. A sprightly breeze masked the interstate noise, and the brilliant, but drying sun blazed down from a deep blue sky.

Day by day I kept my vigil beside the remaining vernal pond. Soon I was sitting at the base of a large black cherry tree that had previously been surrounded by water. Water striders skated over the pond’s surface, and a dead white moth floated in the water. Looking closely, I spotted a few wriggling mosquito larvae. Wood frog eggs were hatching, and some tadpoles had already swum off. Another egg mass lay marooned on the dried shore. A few eggs wriggled in it, so I threw it back into the pond.

No rain fell throughout most of April and into May, as I watched the incredible shrinking pond. The wood frog tadpoles swimming in the water were losing their race against time. In early May I surprised a mother bear and her three small cubs near the pond. The cubs bounded away, up and over Sapsucker Ridge while the sow paused to watch me. Three days later the vernal pond was as large as a small car and three piles of fresh bear scat surrounded it. The wood frogs had lost their gamble, but their eggs and tadpoles had fed turkeys, bears, and probably other wildlife as well.

Not all vernal ponds met the fate that mine did last spring. Some of those on State Gamelands 176 are much larger, and one April afternoon my husband Bruce, son Dave, and I met Jim Julian there. Julian, a Penn State graduate student in ecology, has been studying vernal ponds, and he gave us a tour of one of them. Many wood frog egg masses bobbed in the water, but a few male wood frogs still hid under the leafy detritus waiting for females to appear. I even found two pink dead females, one of which had been chewed on probably by a raccoon, Julian said.

But, unlike our ponds, the gameland’s pond also supported spotted salamanders. One of three mole salamander species that depends on vernal ponds to breed in, they live mostly underground in holes or burrows dug by other creatures and only appear above ground in breeding season. Spotted salamanders are black with yellow spots and lay both clear and opaque egg masses, the latter resembling giant cotton balls.

According to Tim Maret, a biology professor at Shippensburg University who has been studying vernal ponds in Michaux State Forest, wood frog tadpoles eat spotted salamander eggs, and salamander larvae of the same or different species eat each other. As a result, less than one percent of salamanders and frogs hatched in vernal ponds survive to leave them, even if the ponds don’t shrivel up, as mine did, before summer.

Vernal ponds vary in the creatures they support. Another mole salamander, the Jefferson, comes and mates at a pond on a rainy night in late winter. Having previously visited the pond in November and then burrowed into the ground nearby, it will even migrate to the pond over snow, hence its nickname “snow walker.”

The third mole salamander species, the marbled, mates on a vernal pond’s dry land in mid-September. The female marbled salamander lays her eggs under rocks, logs, or in the leaf litter to keep them moist, and she stays with them until the pond fills up in late autumn or early winter. Under the ice-covered pond, marbled salamander eggs hatch and their larvae eat leaves and leaf fungus as well as fairy shrimp, which are inch-long crustaceans that swim upside down through the water. Nicknamed “sea monkeys,” the shrimp drop their eggs into sediment where they remain dormant for months or even years until the pond refills.

Many other species, such as red-spotted newts, pickerel and leopard frogs, spotted turtles, and spring peepers use vernal ponds, but if the ponds don’t contain mole salamanders, wood frogs, and/or fairy shrimp they are not true vernal ponds.

Even though most people are not aware of vernal ponds because they are temporary, many are incredibly old. Several on South Mountain in southcentral Pennsylvania are 15,000 to 21,000 years old, and another pond, near Lewisburg, is 13,800 years old according to pollen analyses of core borings.

Unfortunately, federal wetland regulatory programs don’t protect vernal ponds because they have no direct connection to navigable water. They are built on, bulldozed, or paved over, and developers sometimes use the depressons as storm water ponds. Then runoff from roads and parking lots flow into them, bringing pollution.

Even without direct destruction, vernal ponds can be ruined by logging. Julian says that it is essential to keep forested areas around vernal ponds intact because trees shade the water, reduce evaporation, and control silt runoff, which can suffocate eggs, into the ponds. Instead of the recommended 100-foot buffer zone, he says it should be closer to 500 feet because ponds with wider buffers usually have more species. The salamanders and frogs that visit the pond also need relatively cool, moist, shady conditions nearby to live the rest of their lives.

Wood frogs and salamanders will seek out new ponds if they must, but they are homebodies. Julian told us about one study of 350 marked adult wood frogs, which live up to seven years, that found they all returned to the same ponds year after year. In another study of those hatched in a single pond, he says, 82% came back to breed in their natal pond. Julian also mentioned that a study of spotted salamanders, which can live up to 20 years, found that they returned to their home pond even after it was paved over.

Applying pesticides and herbicides near vernal ponds is another threat to the creatures that live and breed in them. Roundup has a particularly bad effect on them, Julian says, and there are warnings on the label that landowners should read and heed if they care about preserving the vernal ponds on their property.

Acid rain is also hurting vernal ponds, according to Tim Maret. Some ponds he has been sampling have a pH of 4. While spotted salamanders and wood frogs can tolerate such acidity, the rare Jefferson salamanders die if the pH. reaches 4.5 (7 represents neutrality and lower numbers indicate increasing acidity).

Vernal ponds are now on the radar screen of many knowledgeable people. While Tim Maret and graduate student Joe Wilson are documenting the abundance and survival of amphibians in vernal ponds in Michaux State Forest as part of a Wild Resource Conservation Fund project, the Western Pennsylvania Conservancy has received a State Wildlife Grant to find and research seasonal ponds in Pennsylvania, a project that involves a partnership with academic scientists, nonprofit organizations, state and federal agencies and public volunteers. Ongoing studies of these ponds are also being done through the Pennsylvania Natural Heritage Program by biologists with the WPC and The Nature Conservancy.

With all this work perhaps vernal ponds will gain the understanding and protection they need to survive both on public and private lands. I hope so, because despite my disappointment last year, I’m once again watching my vernal ponds. For me there is no better way to celebrate the return of spring.