Each spring, from 2008 through 2011, volunteers and the project biologist looked forward to the first visits to vernal pools in the Deerfield River watershed to listen for the sounds of calling wood frogs. The arrival of wood frogs and spotted salamanders at their breeding pools depends on local weather conditions and varies from year to year. Melting snow, temperatures about 40 degrees F, and rainy conditions prompt spring migration. In years when little or no rain occurs, animals still leave their wintering tunnels and leafy beds for breeding pools. The pools in Greenfield are checked first because the Connecticut River valley is usually warmer and has less snow cover than pools in the higher elevations such as Dubuque Memorial State Forest in Hawley.
The small white objects in the photograph above are spermatophores -- packets of sperm placed on the pool bottom by male spotted salamanders. Females pick up the sperm (located at top of packet) to fertilize their eggs.
In the watershed wood frogs are usually heard calling between March 30th and April 29th. This is for a small sample of 6-7 pools over a four-year period. Wood frog egg masses appear in pools around the same time. The wood frog breeding season is short – usually occurring over a 3-week period in early spring. Males arrive first with females not far behind. Pools were usually checked for the start of activity between March and May. Once we knew that breeding had commenced, we documented vernal pool species by photographing the egg masses of wood frogs and spotted salamanders. This method was the easiest way to prove, for the Massachusetts NHESP, that the pool was certifiable. In 2011 three pools in Dubuque Memorial State Forest were checked every one to two weeks until the end of July. These pools were located along the side of a small hill with each pool at a slightly higher elevation than the last. Each pool was about 200-225 feet away from the other. Here is the chronology of the amphibian breeding season at a pool identified as Hawley St. 3 in 2011:
- April 22: wood frog egg masses observed, as well as mole salamander spermatophores; pool still about one-third ice-covered.
- April 29: spotted salamander egg masses observed.
- May 6: hatch has occurred - hundreds of wood frog tadpoles observed.
- May 26: embryos observed in spotted salamander egg masses.
- June 7: first spotted salamander larvae are observed and their egg masses look “spent” (e.g., eggs have hatched).
- June 26: both wood frog tadpoles and spotted salamander larvae have legs.
- July 15: Dozens of wood frog metamorphs observed at pool edge; in pool are small wood frogs with and without tails.
- July 27: Spotted salamander larvae are 1.5 inches long and walk along pool bottom.
Hawley St. 3 was a fairly large pool with dimensions of about 100 feet by 40 feet. The pool held water all summer, with depths ranging from a high of 18 to 20 inches in spring to a low of 9 to 11 inches on July 27th. During a visit in mid-August the pool was almost as full as it was in early spring. Because of the many rain events that occurred in the watershed during the summer, vernal pools that usually dried up completely or those that usually lost a lot of water, remained filled.
These newly-hatched wood frog tadpoles are staying close to their spent egg masses
Hawley St. 1 was a smaller pool, about 85 by 35 feet. It was located at the highest point on the hill and water depth was 18 inches on April 29th. Here is the chronology of breeding events at this pool:
- April 22: 1 wood frog egg mass observed, as well as mole salamander spermatophores and spotted salamander egg masses.
- April 29: about 20 spotted salamander egg masses observed.
- May 6: dozens of wood frog tadpoles observed – hatch has occurred.
- May 13: pool depth is about 9 inches and some spotted salamander egg masses are exposed to the air.
- June 7: no water in the pool and several spotted salamander egg masses are laying on dried leaves on what was the pool bottom. No amphibians observed.
Vernal pool in process of drying up in mid-August
After June 7th, no water was observed in Hawley St. 1 during three subsequent visits in June and July. The hydrology of these two pools demonstrates several important facts. There is quite a bit of variability in hydrology, amphibians present, and type of soils among pools that are close to each other. In other words, we could not assume that pools that were close together would have similar characteristics. Instead, among these three pools, we observed different plant communities, numbers of wood frog and spotted salamander egg masses, and length of time that each pool held water.
Several spotted salamander egg masses stranded on leaves after pool dried up in late spring
In addition to breeding pools, upland habitats surrounding vernal pools are essential to preserving amphibian communities in the watershed. Biologists studying these animals observed that mole salamanders and wood frogs venture quite far from pools after the breeding season. These animals actually spend most of their time in the forests surrounding the pools. Wood frogs may travel up to 1,600 feet from their wintering sites to their breeding pools, and spotted salamanders up to 1,000 feet. Characteristics of woodlands where spotted salamanders spend their non-breeding time include abundant amounts of logs, stumps, and small mammal burrows. Wood frogs are found in more habitats than mole salamanders, but forested habitats are critical to them as well.