One of nature’s great migrations

The Big Night came as anticipated this year, after a warm day with steady rain. Nighttime temperatures dropped a few degrees and the rain tapered off by sundown, but across the region the amphibians took their cue and were on the move.

My son and I went out at twilight, and right away we saw evidence of wood frogs and spring peepers crossing the roadways. 

There are sections of certain state highways and busy secondary roads that are major migration corridors for amphibians as they emerge from hibernation and seek their preferred wetland types to breed.  

At these places the carnage is considerable, and we avoid them wherever possible on nights like these, but one special spot has a very productive vernal pool very near the road and we make a point of stopping here to help whatever frogs and salamanders are making the crossing.

On this night we got a surprise, for instead of the usual spotted salamanders (Ambystoma maculatum), with their bright yellow spots and torpedo-shaped bluish-black bodies, we found nearly half a dozen of a rarer variety.  

These salamanders were a grayish chocolate color, with paler bellies and flanks spangled with small blue spots. They were thinner than their more robust yellow spotted cousins but roughly the same length. Just to make things more interesting, they may have been hybrids of two mole salamander species that frequently interbreed.

The Jefferson salamander (Ambystoma jeffersonianum) is at the northern extent of its contiguous range here in western New England. These individuals certainly looked like Jefferson salamanders, but they could also have been the result of interbreeding with blue spotted salamanders (Ambystoma laterale). Both of these species were once the same but became isolated from each other by glaciation. There are more blue spotted salamanders east of the Connecticut River and it is safer to consider the two species where their ranges overlap as part of the Jefferson /blue spotted salamander complex.

Jefferson and blue spotted salamanders and their fertile hybrids are listed in Connecticut and Massachusetts. We also found spotted salamanders at two other locations on this night— each time where we previously encountered them — and wood frogs in many more places.

There are wildlife corridors at all scales in our region. Salamanders will travel between 300 and 1,000 feet from their winter hibernation areas beneath the leaves in the forest to the vernal pools where they breed, along with the more common spotted salamander and wood frogs that are likewise vernal pool obligates. 

Protecting the vernal pool does not assure that the rest of the upland habitat is available to these animals during the rest of their life cycles. Where the woods and wetlands are bisected by roads, the salamanders and frogs are at risk on rainy spring nights.  So we go out each spring to help them, as we have done since the kids were small, and are privileged to witness one of nature’s grand migrations that most of us do not even suspect is taking place.

Tim Abbott is program director of Housatonic Valley Association’s Litchfield Hills Greenprint. His blog is at www.greensleeves.typepad.com.