Outdoor Radio: The Hustle And Bustle Of Vernal Pools In Spring

Apr 29, 2015

On an early spring day, biologists Kent McFarland and Sara Zahendra stand in front of a vernal pool in Strafford. It’s noisy.

“The wood frogs are going berserk behind us,” says McFarland. “The sunlight has come down out of the clouds and warmed them up – they are ready to go.”

Zahendra adds that on top of the wonderful noise, you can see the frogs everywhere. “They are jumping all over logs, they are grabbing onto each other. There are these ice patches in the very middle of the vernal pool and they are jumping all over the ice patches. They are all here for one reason: getting ready to mate,” she says.

The Vermont Center for Ecostudies' Steve Faccio, who specializes in vernal pools, joins the biologists at the site. “This is one of my favorite vernal pools around,” says Faccio. “It’s got a wicked big population of wood frogs, spotted salamanders, Jefferson salamanders and fairy shrimp.”

Faccio says that the 50-degree temperature and sunshine, along with the fact that it rained last night, makes the conditions just right for the vernal pool. “This morning when I came, I saw signs that salamanders had definitely arrived by this morning,” says Faccio. “Now that it’s warm … the wood frogs, we can’t even disturb them, we’re standing here talking and they are still going.”

This isn’t always the case, explains Faccio. He says yesterday when he came to the same vernal pool, it was cold and snowy, and when he came near the singing wood frogs, they stopped. “And because it was cold, they didn’t bother to start up again,” he says.

This vernal pool is so full of life because of its size, according to Steve Faccio of the Vermont Center for Ecostudies. Faccio says that it's so deep, it can hold water through August in some years.
Credit Chris Albertine / VPR

McFarland wonders what makes this vernal pool so active and teeming with life.

“I think the size of this one, because it’s so large, it’s so deep, it holds water through July and some years even through August,” says Faccio.

“So, what exactly is a vernal pool?” asks Zahendra. “What makes it different from any other body of water? What makes it special?"

"Vernal pools are seasonal wetlands,” explains Faccio, “They are ephemeral or semi-permanent wetlands that have a few distinct characteristics. One, they don’t have connections to permanent ground water sources, so they are fed by surface water such as rain and snow melt.” He adds that vernal pools are depressions in the landscape formed by a glacier, and that they have been there for a long time.

Another important characteristic of vernal pools is that they eventually dry up each summer. “The big deal about that is it inhibits fish populations from becoming established. These frogs and salamanders evolved in these ephemeral pools without fish, so they didn’t develop defenses against effective predators like fish,” says Faccio.

Some species come to vernal pools particularly to mate because they don't have very many predators in them, says biologist Sara Zahendra.
Credit Kent McFarland

That’s what makes vernal pools so special, says Zahendra. “There are some species that come to these pools particularly to mate, to breed, for their larvae to grow, and it’s because they don’t have very many predators in them.”

Faccio says that there are predators in vernal pools, including invertebrates such as giant water bugs that can eat larvae or tadpoles, but that there aren’t any really effective predators such as fish.

“Last night, at my house, it was the first really good, spring storm we’ve had,” says McFarland. “Thunder, lightening, heavy downpours. That’s when the salamanders came up out of the ground and started walking.”

Faccio agrees and adds that for some, especially the females who have overwintered further away, it’s somewhat of a leapfrog. “They’ll go as far as they can until they start to either get too cold or too dry, and they get underground and wait for the next rain,” he says.

The biologists head into the vernal pool to get a closer look at the salamanders and frogs.
Credit Chris Albertine / VPR

But how do they know where to go? “They use their sense of smell,” explains Faccio. “They use olfaction to migrate to pools, but exactly how they know where the pool is, nobody really knows.” He says that studies have been done that look at where they enter and exit the vernal pools, showing that they enter and exit at about the same point. “Like they are going back to the same area they know,” says Faccio.

The three amphibian enthusiasts head down to look closer at the vernal pool. “I’m overwhelmed, we’re looking at a lot of cool stuff,” says Zahendra. “Is that a Jefferson salamander? We found the holy grail of salamanders.”

Faccio adds that Jefferson salamanders are pretty rare in Vermont. “They are considered a species of special concern. They aren’t state listed as threatened or endangered, but they are one step below,” he says.

Jefferson salamanders are fairly rare in Vermont and are considered a species of special concern.
Credit Kent McFarland

The females leave the pool immediately after they lay eggs, explains Faccio. “The males hang out, hoping to score with another female, and then the adults just go back into the forest. For both frogs and salamanders, this is just their breeding area. The adults, they high tail it out after they are done,” he says. Faccio says that in about a week, the frogs will leave the pool and it will get very quiet. A little bit longer after that, the adult salamanders will leave. 

Biologist Sarah Zahendra holds a wood frog at a vernal pool in Strafford. The adult frogs will leave the pool almost immediately after laying their eggs, leaving them to hatch on their own.
Credit Kent McFarland

They leave the eggs and larvae to develop in the shallow water. “So then when the vernal pool dries up, those who have completely developed, they leave the vernal pool and go into the forest just like their parents did,” says Zahendra.

“And that’s where they will stay until they are mature and ready to breed,” adds Faccio. “For frogs, that’s pretty quick; one or two years. Salamanders can live 15 to 20 years. That’s a long time for an animal that is 8 inches long, lives underground and is cold-blooded.”

The three head back up the hill to seek out the vernal pool that still has remnants of ice floating on the top.

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Outdoor Radio is produced and edited by VPR's Chief Production Engineer, Chris Albertine.