Backyard Naturalist: Salamander season on the horizon

  • A wood frog makes its way across the road during the spring migration season. Photo by Brett Amy Thelen

  • A spotted salamander seen during a Big Night. Photo by Brett Amy Thelen

Published: 3/31/2021 5:16:20 PM

This is the time of year when I start obsessively checking the weather. On any given day, you’ll find me playing and replaying the weather radar, pausing at key moments for closer inspection of the map, and scrutinizing hourly forecasts on four (yes, four) different apps for subtle differences. Will temperatures hover at 41 degrees after sunset or dip to 39? When, exactly, will the predicted rain arrive, and how long will it last? What percentage of the forest floor is still covered by snow in Peterborough? How about in Keene?

Though I spend as much time jawing about the weather at the post office or general store as any self-respecting New Englander, the true focus of my fixation is not meteorological, but herpetological. The spring amphibian migration will soon be upon us and – unlike some migrations that are triggered by shifts in daylight or food availability – it all depends on the weather.

When conditions are right, spotted salamanders, wood frogs, spring peepers, and other amphibians migrate to their breeding wetlands in a dizzying explosion of life known as “Big Night.” It’s a nocturnal affair of mythic proportions.

Big Nights are spurred by three elements acting in synchronicity: thawed ground, nighttime temperatures at or above 40 degrees, and rain after dark. All three must be present to some degree, but there are an infinite number of variations and, as I’m sure you know, spring weather in New England is notoriously fickle. Hence the obsession with weather forecasts.

Classic Big Nights occur after several weeks of warmth – enough to melt any lingering snow and to thaw the forest floor to a depth of several inches or more – when temperatures remain around 45 degrees well into the evening, and soaking afternoon rain continues through the night.

However, if it’s been a dry spring, some amphibians might make their move after a light rain or in heavy fog, when the ground is simply damp. Wood frogs and spring peepers, who famously survive winter by freezing solid, may be more active at marginal temperatures than spotted salamanders or American toads, who need those extra few degrees to really get going. In addition, amphibians will migrate all night long if conditions are favorable, but movement will slow if the ground dries or the mercury drops below 40 – a common occurrence early in the season.

Temperature fluctuations and varying spring snow depth often mean that Big Night occurs at different times in different parts of the region. It’s not unusual, for instance, for Keene’s first migration to take place while Peterborough is still blanketed by snow or, conversely, for Hancock’s salamanders to still be on the move after Westmoreland’s migration has come and gone.

Though it’s tempting to think of Big Night as a singular event, most years see one or two Big Nights, a handful of Medium Nights, and sometimes a smattering of Small Nights. In our neck of the woods, amphibian migrations can occur any time from mid-March through early May.

Whenever it happens, Big Night is pure magic. Under the spell of the spring rain, thousands of amphibians will emerge from the underground burrows where they’ve spent the winter and clamber through the forest – up to a quarter-mile, on tiny feet – to vernal pools and other wetlands for the sole purpose of courting and laying eggs. Their urgency eclipses even their need to eat. In many cases, they’ll return to the very wetland where they first hatched, an unwavering attachment to place biologists call “site fidelity.”

As one friend said, going out on Big Night is “like stepping into another world.” Except, of course, it’s our world.

Like any hero’s journey, the migration is fraught with peril – particularly in places where frogs and salamanders must cross roads to reach their breeding sites. The statistics on amphibian roadkill are sobering: in Canada, biologists recorded an astounding 30,000 dead amphibians over the course of just four seasons along a mere two-mile stretch of road. Researchers in western Massachusetts concluded that roadkill rates on even rural roads were likely to lead to extinction of local spotted salamander populations in as few as 25 years. It doesn’t take a lot of cars to do a lot of damage.

As an individual, one of the very best things you can do for migratory amphibians is not drive on Big Nights. If you’ve got an errand to run and it’s a warm, rainy night, ask yourself if it can wait. You could save the lives of scores of amphibians simply by staying home.

The next best thing – especially if you’re a night owl who doesn’t mind getting a little wet – is to join the Salamander Crossing Brigades, an intrepid crew of community scientists who move migrating amphibians across roads by hand, keeping count as they go.

For fifteen years, I’ve coordinated the Crossing Brigade effort here in the Monadnock Region – complete with volunteer trainings, data forms, Salamander Crossing signs, frequent admonitions to never ever go out on roads at night without a reflective vest and bright flashlight, and even a five-day salamander forecast. We’ve now trained more than 1,200 volunteers, many of whom return, like the salamanders, year after year. Together, we’ve provided safe passage for 53,000 amphibians and counting.

A number of years ago, a fellow Crossing Brigadier affectionately referred to us as “slimy-fingered loonies” – a title I claim with pride. If you think you might like to become a slimy-fingered loony too, you can get more information at harriscenter.org/salamander-crossing-brigades.

Brett Amy Thelen is Science Director at the Harris Center for Conservation Education.




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