The signs of spring are everywhere apparent, from blooming forsythia to the chortle of red-winged blackbirds. However, one of the signal events of the season is invisible to all but the intrepid nature-lover: the night-time migration of amphibians to small vernal pools in the woods, where they breed and lay their eggs.
Spotted, Jefferson, and blue-spotted salamanders and wood frogs breed only in vernal pools—small bodies of water formed from snow melt, which dry up in summer. The mole salamanders, as these species are called, spend most of their lives under a log or rock or in an abandoned rodent’s burrow in the woods, leaving on a rainy or wet night in the early spring to breed (the animals’ skin must remain moist, or they die). Ranging from a few dozen feet up to a quarter of a mile, their journey offers a brief window of opportunity for people to spot these unusual animals and even help save a life, given that many of the migrating salamanders and frogs unfortunately end up as road kill.
The amphibians lay their eggs in vernal pools because the isolated bodies of water lack fish and therefore are free from predators. Each year, it’s a race to mate and lay their eggs early enough so that the larvae, which have gills and tiny legs, develop in time to leave the pool before it dries up in July or August.
Four years ago, Laura Heady, biodiversity outreach coordinator at the New York State Department of Conservation’s Hudson River Estuary Program, launched a program recruiting volunteers in the Hudson Valley to help identify major crossings of the amphibians during the “Big Night,” as the migration is euphemistically called, and carefully carry individual animals across the road, to prevent them from getting hit by speeding cars.
To date, more than 165 volunteers in nine of the counties bordering the Hudson River have surveyed roads and documented migrations, recording 20 species (including other species of salamanders, frogs and toads, which don’t breed in vernal pools) and more than 7,000 individuals. Unfortunately, the mortality rates are high: last year, for example, 1,294 live salamanders and 860 live frogs and toads, and 424 dead salamanders and 196 dead frogs and toads were recorded.
While the wood frog and spotted salamander, which is the largest of the three species, measuring up to eight inches in length, is common, the Jefferson, blue-spotted, and a fourth species, the marbled salamander, which migrates to the pools in the fall, have declined and are listed as species of special concern by the state environmental authorities.
Heady has been traveling around the Hudson Valley giving presentations to the public in an effort to raise awareness about the ecological value of vernal pools, which aren’t protected by the state or federal government. These small woodland bodies of water have been wantonly destroyed by development. While many homeowners in the region unfortunately view vernal pools as mosquito-breeding waste places and bulldoze them away, in fact the pools are the basis of a rich food web, starting with the leaves that have fallen into the pools, which feed algae and larvae from the invertebrates. Heady calls them the “coral reefs” of the forest and noted that the pools also help absorb excess water, helping mitigate flooding.