Why did the Salamander Cross the Road?

APRIL 2024

You can tell it’s spring from the classic harbingers of the season: ephemeral flowers such as skunk cabbage and trout lily pop up, maple trees bud, and insects buzz. Or you can turn to a calendar. With no concept of weeks, months, or daylight savings—frogs and salamanders rely entirely on environmental cues of temperature and precipitation to tell them when it’s time to start their vernal lifestyle. What does this seasonal shift look like, and how have humans affected it?

Frogs and salamanders in winter

Amphibian’s winter survival strategies vary depending on species. Some frogs such as bullfrogs (Lithobates catesbeianus) and green frogs (Lithobates clamitans) spend the winter nestled under ice in wetlands and in the lake’s shallows, and typically remain there to breed in the spring and summer months.

This is not the only method. Other frogs such as spring peepers (Pseudacris crucifer) and wood frogs (Lithobates sylvaticus) as well as “mole salamanders”—a group of salamander species unique to North America with a tendancy to burrow underground—including Jefferson salamanders (Ambystoma jeffersonianum), blue-spotted salamanders (Ambystoma laterale), and the iconic spotted salamander (Ambystoma maculatum) employ a different strategy. They all overwinter in wooded upland areas: the mole salamanders tucked deep underground beneath the frost line, spring peepers a bit shallower in mud and duff, and wood frogs in the upper layers of the forest floor where their bodies freeze solid for up to eight months.

Big nights out

The frogs and salamanders who spend the cold months in the upland woods get moving once temperatures rise and the land begins to defrost. They need to make the journey from their wintering grounds down into lower lying wetlands to mate. It takes a combination of environmental factors to trigger the migration—thawed ground, temperatures above 40 degrees F, and wet weather. When these three conditions are met, it’s go time.

Migrating amphibians move at night to avoid predation. They travel upwards of a quarter mile (a considerable distance for such small creatures) to breeding pools. On the first warm, wet night of the year, frogs and salamanders can be seen heading to wetlands in droves during what herpetology enthusiasts term the “Big Night”. Really, these migrations happen in pulses, so it’s more apt to call them “Big Nights”.

Typically, Big Nights occur between mid-March and mid-April. With climate change increasing the volatility and variability of temperatures in late winter and early spring, amphibians may emerge from hibernation earlier or over the course of more “Big Nights”. Changes in phenology, or the natural seasonal timing of a species’ activities, can create new challenges in community structure and resource availability. And that’s not the only way we’ve created problems for amphibians on their mating journey—our roads add stressors and can make for a perilous trip.

Roadway threats to amphibians

One issue that may not immediately come to mind is the heavy salting of thoroughfares in our region. Road salt dissolves and increases the salinity of ground and surface waters, including the vernal pools in which wood frogs, spring peepers, and mole salamanders breed. According to research from SUNY College of Environmental Science and Forestry in Syracuse, spotted salamanders and wood frogs are particularly sensitive to salt. They are only half as likely to be present in salty breeding pools near roads and larvae survival is significantly reduced in conditions of moderate to high salinity.

However, cars have the most direct roadway effect on amphibians. It’s common for them to have to cross roads when moving between their upland hibernation areas and lower lying breeding zones. The fragmentation of these two habitats can be fatal to them—research indicates that mortality from automobiles can significantly decrease local populations of mole salamanders and the extirpation of certain species is almost entirely attributed to car strikes.

How you can help

The good news is you can get involved locally to help the frogs and salamanders! Homeowners can take action by reducing or foregoing salt use on driveways and paths—check out LCC’s tips on salt reduction here for more information. When possible, you can also avoid driving on potential “Big Nights” when it’s warm and rainy.

For additional hands-on participation in springtime migration and conservation efforts you can help amphibians cross the road. The New York Department of Environmental Conservation organizes the Amphibian Migrations and Road Crossings Project, and the North Branch Nature Center in Montpelier VT runs an Amphibian Road Crossing Program. Both entities provide a host of training materials and guides on how to become an amphibian crossing guard, record what species you encounter, and safely ferry them across byways. Volunteers often bring family and friends or coordinate with each other to make a social night of high-vis vests and frog spotting. While our transportation corridors hinder amphibians and contribute to their population declines, participating in programs like these can help more of them live to see another spring.

Lake Look is a monthly natural history column produced by the Lake Champlain Committee (LCC). Formed in 1963, LCC is a bi-state nonprofit that uses science-based advocacy, education, and collaborative action to protect and restore water quality, safeguard natural habitats, foster stewardship, and ensure recreational access. You can joinrenew your membership, make a special donation, or volunteer to further our work.