Getting ready for The Big Night

Sun is shining and birds are singing! You know what that means: spring is upon us, and some very important ecosystems are becoming active once again. Among the most critical and vulnerable of these ecosystems is the vernal pool.

What’s a Vernal Pool?
The quintessential vernal pool is an isolated, semi-permanent wetland that comes to life seasonally. These natural depressions fill up with water in the fall due to a rising water table, or fill with snowmelt and spring rains. Vernal pools can be found in meadows, floodplains, woodlands, and even sandplains across the state.

Vernal pools often freeze over during the winter, but as temperatures rise when spring approaches, a vernal pool becomes an active breeding zone for many creatures from invertebrates to amphibians and turtles.

Vernal pools are vulnerable to development. Even if a vernal pool itself is saved from destruction, changes in the surrounding upland may disrupt the habitat and life cycles of the resident species. The removal of the surrounding forest during the construction of houses, driveways, and lawns, for example, may degrade a nearby vernal pool to such an extent that the amphibian population is eliminated.

Home Sweet Vernal Pool
Vernal pools host several obligate species, or species that require the use of a vernal pool for either a portion or the entirety of their life cycle. Importantly, due to the temporary nature of this environment, vernal pools do not accomodate populations of fish, which would eat the eggs and other life stages of most vernal pool-related organisms.

New England is home to many easily recognizable obligate vernal pool species, including:

• Salamanders Yellow-spotted, marbled, blue-spotted, and Jefferson salamanders rely on vernal pools for reproducing (critical for the latter three as they are rare, state-listed species). Most of these critters live in burrows on the forest floor, or underneath logs and rocks. On the first warm rainy nights in the spring, watch for salamanders crossing roads on their way to vernal pools.
• Wood frogs During the first few weeks of the breeding season when the temperature hovers around 50°F, males join in a quacking chorus from vernal pools, calling out to potential mates. After mating, wood frogs return to their moist woodland habitat, where they spend the year. Their eggs hatch in the vernal pool, and the resulting tadpoles develop before following the adults upland.
• Fairy shrimp These incredible creatures range in size from ½ inch to 1 ½ inches, swim upside down with 11 pairs of legs, and spend the entire year in vernal pools. They survive dry periods as eggs, which hatch when the pool refills  with water. Fairy shrimp need only a few weeks of water in the pool to complete their entire life cycle.

Experience Big Night
Every year, during one of the first warm, rainy nights of the spring season, wood frogs and salamanders begin the migration to vernal pools to breed. That evening is referred to as The Big Night.

Mass Audubon’s wildlife sanctuaries across the state celebrate the event with all sorts of wonderful programs throughout the month.

Had the chance to see it for yourself this year, or in years past? Tell us about it in the comments!

– by Emma Evans