In 2007, the Dummerston Conservation Commission received a grant from the New England Grassroots fund to inventory the vernal pools of Dummerston develop an ongoing monitoring program, and work to protect the town’s most important pools. Oh yes, and to put together the information on this website. From here you can navigate to general information about vernal pools, learn more about their inhabitants, see a map of the vernal pools of Dummerston, and find out how to become a vernal pool monitor.
What is a Vernal Pool?
There are many ways to define “Vernal Pool.” Because we are interested in the specialized habitat they provide for a suite of creatures, we like the definition provided in Elizabeth Colburn’s book, Vernal Pools, Natural History and Conservation:”
Woodland context: vernal pools occur in or next to forests or other wooded areas
Isolation: vernal pools lie in confined basins with no continuously flowing inlet or outlet, and they have no continuous surface-water connection with permanently flooded water bodies.
Size: vernal pools are small and shallow.
Hydrology: vernal pools fill seasonally attaining their maximum water levels and volumes in the spring; they dry up annually or every few yearsâ€”standing water either disappears completely, or water levels drop substantially during the summer, exposing most of the pool bottom and retaining only a fraction of the peak volume
1) Hold water long enough so the young amphibians and invertebrates have time to
2) Dry up often enough that larger aquatic predators such as fish, bullfrogs, and certain dragonflies, can’t
Usually the pools are located in the woods where they’re protected from the sun, and form in shallow basins where spring rains and snow melt collect. Each spring and early summer they teem with life, which then disperses into the forest when the amphibians mature, making vernal pools an important part of the entire forest food chain.
Vernal Pool Amphibians
A member of the group called the mole salamanders, the Spotted Salamander, Ambystoma maculatum, leads a life similar to that of those little gray mammals. They spend most of their lives alone in dark subterranean networks of mammal tunnels. Here they stalk their wily prey, earthworms and other soil invertebrates.
The big event on the Spotted Salamander calendar is their annual sojourn to their breeding habitat. The preferred habitat for this activity is a woodland vernal pool. It is on these treks to their breeding pools that we have the best opportunity to see these amphibians. They are up to 9 inches long, gray to black, and each salamander has a distinctive pattern of yellow polka dots on its back. The belly is usually pale gray, but can sometimes have lighter speckles.
The females can be distinguished from the males on their way to the pools because their sides are plump with eggs. Once in the pools, the males gather in groups called congresses. The congress at its peak can be a sphere of up to 200 undulating swimmers, yes it’s the Salamander Ball! The bottom of the pool will be dotted with spermatophores, the white packets of genetic material excreted by the males. When a female arrives and has been sufficiently stimulated by gyrating males, she and a suitor will leave the ball, and he will beckon her to follow him with his waving tail. He will lead her to his spermatophore. If she is suitably impressed, she draw it into her cloaca to fertilize her eggs. She will lay a cluster of 100 – 300 eggs attached to a stick or pond vegetation. After the eggs have been laid, courtship is over and that salamanders return to their lives. (There are many accounts of Spotted Salamander courtship, and the details don’t always match. According to some, females select spermatophores at random. I suggest that you visit a pool on the night after salamander migration and see for yourself.)
The young salamanders wriggle free of their jelly coating after a month or two. The warmer the water temperature, the sooner they hatch, but the warmer the temperature, the sooner the pond will dry up. Each year it is a race with the sun. The larval salamanders have feathery gills and very soon develop legs, but it takes a few more months for them to be ready to join their kind on land. Many vernal pools will dry before this metamorphosis can be completed. Fortunately, Spotted Salamanders can live 20 years, so the adults have other opportunities to reproduce.
Rare in most of Vermont, the Jefferson’s salamander is common in some of Dummerston’s vernal pools, and even outnumbers spotted salamanders in some of them. These salamanders have light blue flecks on a brown to gray background. The flecks are mostly on the stomach. Jefferson’s can be up to 7 inches long. Like the spotted salamanders, Jefferson’s migrate from upland habitat to vernal pools each spring to lay their eggs. They often arrive at the pools earliers then the spotted salamanders.
These salamanders often hybridize with blue-spotted salamanders the next salamander on this list. The hybrids are nearly impossible to tell from the purebreds, so we call the salamanders that look like Jefferson’s Jefferson’s complex salamander’s.
Blue Spotted Salamander
Blue-Spotteds are significantly smaller than Spotteds, measuring only 4 – 5 inches in length, and a Windham County rarity. They have bright blue to white spatters on a bluish-gray to black background. These spots are sprinkled liberally and randomly over the whole salamander. The pale flecks on a Jefferson’s tend to be concentrated on the sides and belly.
If you read about Jefferson’s salamanders, above, you know that where these species’ ranges overlap, hybrids are often more common than either pure species.
These two species and their hybrids form a group we call Jefferson’s Complex. Most sensible sexually reproducing species have chromosomes that are arranged in matching pairs in most of their cells, a condition called diploidy. Eggs and sperm each contain one set of chromosomes (haploid). These chromosomes merge when an egg is fertilized and a new diploid life begins. Many of the hybrids, however, are triploid, tetraploid, or even pentaploid. Most of the hybrids are females. Many of these hybrids reproduce by gynogenesis. This means that the egg requires a male sex cell to become activated, but it does not fertilize the egg. When the female produces eggs, the numbers of chromosomes are not reduced. The egg develops into a clone of the mother.
However, some research indicates that gynogenesis in these salamanders is temperature dependent. When temperatures are 60 degrees F or warmer, the egg will be fertilized, and the male chromosome will be added to the female’s (making the offspring of a diploid female a triploid, etc.) If water temperatures are cooler than 41 degrees F, reproduction will be through gynogenesis.
So, what do we call those speckled salamanders that don’t have yellow spots? Nearly all of them in our region look more like Jefferson’s than Blue-Spotteds, and since we can’t tell without checking the DNA, we consider them Jefferson’s Complex. If you find one speckled like the one in the picture above, though, it might be the less common Blue-Spotted, or a hybrid in which those genes are more numerous. Note such salamanders as Blue-Spotted, and please take a picture!
The Wood Frog, Rana sylvatica, is the frog with the most northern distribution in North America and can be found in the forests of Alaska and Canada. These frogs overwinter beneath the leaf litter, and by increasing the percentage of glucose in their cells, are able to withstand the freezing of up to 1/3 of the fluids in their bodies with no ill effect.
A favorite meal of many predators, wood frogs rely upon their ability to blend in with leaf litter to survive, that and their prodigious ability to procreate. Each female will lay between 750 and 1,500 eggs per year. Although only 4% of these survive to become fully metamorphosed froglets, according to one Alaskan study, that still results in 30 to 60 little frogs per coupling. Even if, as another study indicates, seventy percent of these move up the food chain in their first year, that still means that the frogs that arrive at the pools to breed each spring have a good chance of replacing themselves. It also indicates the importance of wood frogs to the rest of forest life.
In spite of these attributes, these frogs, like all amphibians, have vulnerabilities. When vernal pools dry early, the entire year’s offspring might be lost. The frogs are also susceptible to bacterial diseases, environmental toxins, and ultraviolet radiation. Your efforts to help them reach their breeding pools will not only ensure the continued life of individual frogs, but will strengthen the local population of these important and interesting creatures.
No one knows for sure how these frogs find their breeding pools. There is evidence to suggest that they use olfactory and celestial cues. It might be that they follow gradients of increased humidity down hills to the pool basins.
Once there, the males begin the mating calls that make the pools sound like the cafeteria at a duck school. These frogs have vocal pouches near their front legs, so you will see their sides expanding as they croak, rather than their throats. Each female is likely to be swamped by suitors, and she is lucky if she can swim away with just one male gripping her back in the embrace called “amplexus.” Once she arrives at the egg laying site, often a site used by many females, and begins laying eggs, the male releases his sperm and stirs the water with his hind feet. After the eggs have been laid, they part, and without so much as a “See you next year,” the male heads back to try his luck again. The females usually sink to the bottom after this amorous encounter, and leave the pool as soon as they are able.