(Originally posted March 25th, 2021, updated for 2024).

In like a lion, eh, Spring? The weather has been totally fantastic here in Burlington. We’ve got garlic shoots coming, grackles moving through in big numbers, house finches with nesting material see image below), and buds starting to green up on our lilacs. But of all the spring phenology events, my favorite is amphibian migration. My friend Ian sent me photos from some Eastern newts and spotted salamanders moving last night by North Beach. And it looks like we could be in for another early Big Night this year. The weather looks perfect at this point for a big movement of amphibians tomorrow night (Friday, March 26, 2021. In 2024, the movement may be as early as February 28)!! Read on for more.

Female housefinch with strands of grape bark in her mouth - it's nesting season! (Backyard, Burlington)

What are Big Nights?

Before moving to Vermont I’d had encounters with breeding amphibians. But I’d never really had any sense of the shifting patterns of frogs and salamanders over the course of a year. My first year in Vermont (back in 2008), my grad school adviser told me about “Big Night,” which conjured up some mystical and rowdy barn dance under a dark starry sky. That phrase has wholly captured my attention, and each spring I eagerly await the just right conditions to briefly encounter amphibians on their nuptial quest. And the phrase has definitely lived up to its reputation.

As I first learned it, Big Night refers to the first big movement of amphibians from their overwintering sites in upland areas down to their breeding grounds in wetlands. It more frequently happens in pulses as amphibians make the arduous journey (more cold tolerant species like wood frogs and springs peepers move earlier, toads, leopard frogs, and others move later; the call chart below is a good indication of their relative movement times), so it’s better to think of these movements as “Big Nights.” Throughout March and April, when the conditions are right, you can get hundreds and hundreds of sleepy frogs and salamanders rousing to the call of nature and stumbling over hummocks to the water’s edge.

Pair of wood frogs in amplexus, the male hitching a ride across the road on Big Night (Shelburne Pond, Shelburne)

Conditions for Big Night

I was told as a rule that amphibians didn’t start to move in the Burlington area until the 2nd week of April. But since moving here, this rule has failed more than it’s applied – I even recorded amphibians moving as early as March 8th back in 2012!! Here are the factors that I use to predict if amphibians will be moving (and the more these conditions all sync up, the more likely you’ll get a big flush of amphibians):

  • Snow has mostly melted: Spring peepers and wood frogs essentially freeze solid in the leaf litter, so you need for not just the snow to melt, but the ground to warm up above freezing as well. You can occasionally will get cold-adapted species (like spotted salamanders) moving over patches of snow.
  • Temps >37ºF: The warmer the better. Being poikilotherms, amphibians depend on ambient temperatures to warm up their bodies. Warm weather means warm (and therefore active) bodies. While they can move at temperatures lower than 37ºF, the warmer the better. Some species, like gray treefrogs and American toads don’t sing until it’s above 50ºF.
  • Wet roads and/or raining: A good soaking rain will bring out the amphibians. Remember that amphibians are moving through wooded areas, so even if it’s wet on the road from a light mist, this might not have wet the forest floor.
  • Night time: Running the gauntlet from winter site to breeding grounds is scary business. Amphibians move at night in part to stay hidden from predators. Keep your eyes up – I often see barred owls out hunting amphibians.
A spotted salamander who clearly didn't get the message about waiting for the snow to melt (Pond Rd, Shelburne)

Where to go for Big Night

There’s no one recipe we can use to cook up the life history of all our species of amphibians, but there are definitely some general patterns we can use to track down good spots to see them. Generally they overwinter in upland sites (some, like green frogs and bullfrogs, have tadpoles that overwinter in ponds). And generally they come down from their overwintering sites to breed in wetlands (some species, like red-backed salamanders, however, breed under rotting logs or rocks in upland sites). These vernal movements can be hard to see unless there’s a road in between their overwintering sites and their breeding sites. As exciting as these road crossings may be for us, they can be a devastating trial for the amphibians. I’ve found a few spots by driving around on warm wet nights with my windows down (listening for that tell tale “peep”) and my brights on. There are a few really stellar spots – Pond Rd in Shelburne or Monkton Rd (link) – but there are just as many other smaller spots that are equally exciting. So get out and explore when the weather’s right!

The paparazzi discovers a wood frog at Big Night for amphibian crossing (Shelburne Pond, Shelburne)

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