Vernal Pond Adventures
The largest of our vernal ponds in early April.
Once again I’m sitting beside our mountaintop vernal pond and wondering if this will be the year the wood frogs will make it out of the pond before the water disappears. A wood frog’s life span is about seven years, and for six years the pond has dried up before the wood frogs’ have fully developed. Some years their eggs are left high and dry; other years their tadpoles are.
A vernal pond is a temporary, fish-free wetland that fills in late winter or early spring and dries out by early summer in a good year. This pond is only several yards across and several yards long, depending on rainfall, and, unlike the tiny, 6-foot-wide pond at the base of First Field, I can’t get close enough to watch the courtship and mating of the frogs. I can hear their quacking calls, though, and I enjoy watching a wide variety of wild creatures that visit it even when I’m sitting quietly beside it, my back against an oak tree.
I find it incredibly peaceful to watch the pond as it reflects the trees in its still water. But this early March day a skim of ice over it glitters in the sunlight. Its surface has a medley of half circles and triangles artistically rendered by the ice-maker overnight.
On the thirteenth of March, as I near the vernal pond, circles appear in the water. I wonder if they can be disappearing wood frogs. I study the still, dark water and spot one small mass that I look at through my binoculars. A golden eye returns my gaze. I move closer and see a male wood frog stretched out in the water. Next to him is a stick with two clumps of wood frog eggs clinging to it. This unusually bold wood frog dives into the water but quickly resurfaces. Since I am still standing there, he sinks back under the water.
The vernal pond has already contracted, and I hope that the dark clouds rushing across the Allegheny Front will drop some rain on us and fill up the pond. But it doesn’t happen. Nevertheless, two days later, I find two wood frog egg masses in different areas. The gelatinous, fist-sized blobs contain several hundred eggs with black embryos.
By the 22nd of March, I count four separate egg masses, but the vernal pond is still shrinking. If the rain comes soon enough, the eggs may survive. And come it does, raining hard from 1:00 a.m. until mid-morning on March 24, filling up the vernal pond again.
The vernal pond in mid-March.
It’s almost a month before I return to the pond. At the beginning of April, while hiking on Sapsucker Ridge with my sixteen-year-old granddaughter Eva, she steps on a branch and I trip over it, my left leg landing hard on a pointed rock. Nothing is broken or fractured the doctors tell me, but my leg and foot swell up and turn black and blue. I have, after all, injured my tibia, the bone just below my knee. After days of being veranda-bound and more days of slow, short walks, I finally make it back to a vernal pond seething with insect life, most notably water striders walking atop the water and looking for mosquitoes resting on the water just after they have emerged from their “wriggler” larval stage.
Various species of diving beetles also swim in the water on the hunt for invertebrate and vertebrate creatures, including the wood frog tadpoles. I have always marveled at how these insects find a vernal pond, especially this one, isolated on a mountaintop half a mile from the nearest stream and that one intermittent near its source. Apparently, they are able to fly to it from such water. But some species of diving beetles actually overwinter in the basin formed by a dried up vernal pond.
The wood frog eggs have long since disappeared from sight, colonized by the symbiotic algae Oophila amblystomatis, which turns them green. It’s been cold most of the month, delaying the hatching of the eggs. But near the pond I stop to admire the patch of spreading spring beauties, the only place they grow on our property. This is an open, mixed-oak forest close to our neighbor’s logging operation that took place several years ago. Not much has regenerated and the vernal pond is not as shaded as it used to be.
It’s now the fourth of May and torrid summer weather has returned. I practically stumble over a porcupine as I approach the vernal pond and send the creature scrambling up a large red oak tree. The vernal pond is a veritable tadpole soup—tadpoles by the dozens wherever I look, floating near the surface to warm themselves up now that the trees have leafed out and are shading the pond. They need the solar heat to develop quickly into frogs before the pond dries up. First they graze on the symbiotic algae still clinging to their gelatinous cradle, and then they feed on algae and leaf material on the pond’s bottom. They also may feed on each other, those that hatched first preying on the latecomers.
Three days of hard, cold rain follow, and once again the vernal pond is overflowing and seeping over into a series of wallow-sized pools. My pond-watching becomes an almost daily discipline as I sit and watch the tadpoles eating, swimming, and basking in patches of sunlight. In mid-May I hear clucking as a hen turkey circles behind me. Maybe she is hoping to catch some tadpoles for brunch.
Water striders
Often the tadpoles join in aggregations of ten on a submerged stick. Then there is a sudden flurry and they separate, but in a few seconds they gather together again, performing their own watery tadpole ballet. In addition to basking in the sun, perhaps they are finding refuge from predators in a crowd like flocks of birds do.
By the twentieth of May a few of the larger tadpoles are developing back legs. I sit close to the water and watch as the tadpoles continually surface to feed on the detritus floating on the water, then submerge, each tadpole swirling the water into a circle. I try counting the circles to figure out how many tadpoles still inhabit the pond, but the confusion of circles quickly confuses me. Instead, I settle back and enjoy the ambiance of the pond and surrounding woodland having long ago learned to tune out the occasional train whistle and the constant traffic noise on Interstate 99 at the base of the ridge.
A mourning dove sings without ceasing. Red-eyed vireos, eastern wood pewees and a scarlet tanager frequently add their songs to that of the doves. Water striders skate along the water. A common green darner dragonfly buzzes over the pond. Then an American crow flies in like a kamikaze fighter plane, veers when it sees me, and silently retreats.
There are more days of rain and again the pond overflows. The pond water is so dark that I can’t glimpse the tadpoles, but dozens of circles that gradually subside as I sit in front of the pond indicate their presence. Sitting beside the pond, a sudden nearby gunshot startles the tadpoles as much as it startles me. Not only do they have sharp eyes but sharp ears too.
Near the end of May, I’m serenaded by a robin and scolded by a hairy woodpecker while I sit beside the pond. I also see a dark-eyed junco, which should have been breeding farther north on the Allegheny Front or beyond by now. A mourning dove flies in to catch insects from the pond and goes off in a flurry when it realizes I am there. A black-and-white warbler sings. Chipmunks scold. Mosquitoes that probably have hatched in the pond circle me and force me to move on after I catch a glimpse of a few more tadpoles with back legs.
My vigil continues in June. By then, I wonder if those tadpoles will ever change into bandit-masked wood frogs. On June 8 many heads pop up from the water and stay up even though most tadpoles still have tails. Two male robins hold a song fest while a female chases all comers to the pond as her spotted youngster bathes. Later a tufted titmouse takes a bath. Chipmunks chase around the pond and one scampers up to me, pauses at my feet to look, and then continue its race with its rival. A pileated woodpecker pounds on a nearby tree trunk.
Wood frog in mating season (in the tiny, spring-fed pool at the bottom of First Field)
All the while a pleasant breeze blows, keeping biting insects away. The pond is slowly shrinking, but it is still a bathing and watering hole for birds and mammals alike.
The following day I spend another session at the vernal pond serenaded by the same two robins. Little mouths surface to catch detritus spread atop the pond, and once I see a tiny froglet hopping over a small section almost as if it could walk on water. Froglets are supposed to be between a half and 7/8th of an inch when they metamorphose. Their watery life is ending and none too soon.
A chipmunk approaches me with much trepidation, and when I don’t move, it goes to the pond and drinks. Then it scampers off.
Suddenly, the robins begin high octane scolding as if, after half an hour, they finally notice me. On and on they scold, but at last they subside.
When I am too stiff to sit any longer, I get up and walk back to the field path. There I find an enormous pile of fresh bear scat that wasn’t there before. It looks as if the robins were scolding a bear.
A couple days later, as I’m sitting by the pond, I hear crashing in the woods that sounds like a bear. Sure enough, one approaches the pond, and I ponder my position. It’s obviously hoping for a drink and doesn’t see or scent me. At last I stand up, and the bear looks up, sees me, and flees.
The vernal pond continues to fill every time it rains, and slowly the froglets depart, although I don’t see them. But there are fewer circles in the water, less little heads surfacing, every time I visit. How wonderful that after so many springs when the pond dried up too soon, our aging population of wood frogs will finally get some newcomers. The young frogs will spread out, traveling up to several hundred meters in all directions, making new homes in the leaf litter, and preying on a variety of arthropods.
But even as the pond shrinks and the froglets leave, I still seek quiet time beside it. One day, late in June, I encounter an eastern box turtle, floating in a couple inches of water, its eyes closed. At first I think it is dead, but when I touch it, it opens its eyes. Later, I learn that eastern box turtles like to soak and feed in vernal ponds.
Wood frog found under a rock in Plummer’s Hollow Run in September
On another day, two doe wander past me and water at the pond while I sit a few feet away. Then they continue on their way. They never do detect my presence.
I can only wonder how many other wild lives are impacted by this small pond. Even though knowledgeable foresters will steer logging operations away from such places, most loggers either don’t know or don’t care about such refuges. Or they begin their logging operations in the fall when the ponds are dried up and they don’t recognize them for what they are.
My own life has been enriched by our vernal pond this water-full spring. Even after it is completely dried up, in broiling hot, droughty July, I wander back to sit under the oak shade. Where have all the wood frogs gone?
One day, on my daily walk, an adult wood frog hops across my path.
“There you are,” I say out loud as it hops quickly out of sight.
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.
Marcia with golden eagle (photo by Todd Katzner)
Marcia Bonta is the author of nine books and over 300 magazine articles. The blog portion of this website includes her popular “Naturalist’s Eye” column from Pennsylvania Game News, reprinted here on the 1st of each month. Unlike typical blog entries, these columns are written months in advance, usually about things that happened during the previous year. Read more…
