Vernal Pools – A Road Less Traveled

by Jamie Bogart, Lloyd Center Research Associate

We are perhaps never more thankful for, or more in need of, a connection to the nature that surrounds us than now. While we miss large group excursions to natural areas for guided educational tours, we are fortunate to still have access to the landscape. Provided we obey current social distancing measures, some nature properties, including the Lloyd Center, remain open. If you’re lucky, you may possess a backyard large enough and located such as to see wildlife activity out of your own window.

Songbirds are a bonus during this time due to backyard feeders, to the tune of large flocks of hungry blackbirds that are currently taking over feeders as a signal that spring has sprung. These include the Common Grackle, Brown-headed Cowbird, and most notably the Red-winged Blackbird, the first spring migrant songbird to return. The Cornell Lab of Ornithology, which established Project FeederWatch to focus mainly on winter birds, has actually extended its season through May, to accommodate the stay-at-home advisory. On treks into the Lloyd Center to check on and feed animals during this time period, we continue to tally abundance and diversity as a year-round study, and will be continuing with Project FeederWatch surveys during this period.

But while backyard wildlife is a blessing, the coronavirus lockdown has us pressed for both time and space. We are less likely to see more hidden activity that exists across the vast landscape. From a woodland trail at the Lloyd Center, we might notice a wandering deer, turkeys feeding, a squirrel hoarding, a raptor soaring, a woodpecker drumming, a Barred Owl calling, a Carolina Wren singing, or a Northern Flicker in flight. If we’re lucky, we may see the flicker fly back to its nest hole in a tree cavity. But in this new world of “quarantine”, we probably won’t go bounding off trail through the forest to investigate a more obscure one.

An exception to this rule was on display on a recent trip into the Lloyd Center, when I noticed a sound that over the past few weeks has become commonplace, the “quacking” call of breeding Wood Frogs. The pandemic incidentally is coinciding with territorial activity of a variety of wildlife including the fabled American Woodcock which puts on highly visible displays, and at ground level, the precise breeding phase of certain vernal pool organisms that are seldom seen. Vernal pools are often the temporary water bodies that attract breeding amphibians, which at night, crawl to the pools to mate and lay eggs around the first spring rains. The Lloyd Center surveyed potential vernal pools (PVPs) on public property in Dartmouth (2001) and private properties in Rochester (2002) (click here for more information) through the then Buzzards Bay Watershed Initiative. Many of these pools now officially certified. Vernal pool certification prevents destruction of vernal pools and limits activities allowable in their buffer areas. For further information on vernal pool certification see www.mass.gov.

Vernal pools can be large and situated at a forest edge near trails, such as those at the Lloyd Center within its Red Maple Swamp and in the Kettle Pond (with the bird blind near), and therefore be convenient for education and study. But vernal pools can range in size from tiny to quite vast, with the primary criterion being a lack of fish populations that would prey upon the eggs. This usually means no connection to streams through which fish can travel, making small temporary ponds deep in the forest especially optimal for amphibians. It should be noted however, that many pools, including the Lloyd Center Red Maple Swamp and Kettle Ponds that contain amphibians, are permanently flooded wetlands.

The Wood Frog calls attracted me to two separate forest interior pools. The frogs quickly quieted as I approached and none were visible, but I saw eggs of the Spotted Salamander at the bottoms of the pools. Spotted Salamander eggs are either a clear or cloudy (pictured) mass, and always a more firm mass compared to Wood Frog eggs (pictured) which are a clear, loose mass that slips through one’s fingers. Another pool I had passed earlier, off of our Hardscrabble Trail close to the Slocum River, had just enough water to inundate Spotted Salamander eggs; the discovery of these egg masses being what prompted me to go back and investigate the source of the Wood Frog racket.

One trait common to all vernal pools is a tight window of activity within which to efficiently find evidence. Although Wood Frogs have tadpoles and Spotted Salamanders have larvae, the egg masses are more visible but present for a relatively short period. While the breeding time frame for these species is similar, the egg-laying window for Wood Frogs is often slightly earlier, and their egg masses may have already hatched at these particular pools. An invertebrate species, the Fairy Shrimp, also requires vernal pools, and when present, exists in high numbers for an even shorter time frame, about two weeks. Their short life cycle is perfectly adapted to the temporary nature of vernal pools. Wood Frogs, Spotted Salamander, and Fairy Shrimp are called “obligate” species because they rely heavily on vernal pools, and are considered evidence during the certification process. If obligate species aren’t present, pools can still be certified using a combination of “facultative” species (e.g. Pickerel Frog, Green Frog), those that don’t require, but frequently use, vernal pools. Biologists sometimes return to dry pools later in the season to complete vernal pool certification using other evidence left behind.

Vernal pools are critical wetland habitats for forest dwelling amphibians, and are an important and fascinating aspect of the biodiversity in the region that we are striving to preserve and protect. But even under normal circumstances, vernal pools are hidden jewels that fall under the radar. If you’re fortunate enough to live near a vernal pool, know where one is, or hear those Wood Frogs quacking on a forest walk, consider checking it out. Or if you miss the window and find yourself standing in a vernal pool gone dry, you can rest assured the picture will change next year when the cycle repeats itself.