Are reptiles and amphibians likely to be on the roads tonight?

What a Big Night is

Many frogs, toads and salamanders spend most of the year in the woods and travel to small ponds and wetlands to breed. In much of the eastern United States and Canada, they make that trip on rainy nights in late winter and spring. Most of this movement happens after dark, and much of it is packed into a few nights each year.

Crossing programs in New England and New York call the biggest of these nights a “Big Night.” Most years bring one or two Big Nights and several smaller ones.

Their routes often cross roads and long driveways, and animals die there even where traffic is light. On one small two-lane road in California, where nighttime traffic averaged about 27 vehicles between 8 pm and 5 am, about 39% of the newts crossing during one breeding season were estimated to have been killed. On four roads surveyed in Indiana for about 17 months, 95% of the 10,515 dead animals counted were amphibians and reptiles. A study of spotted salamanders found that losing more than about 1 in 10 adults to roads each year can lead to a local population disappearing.

Warm rain after a cold spell

In the Northeast, crossing programs look for three things together: thawed ground, evening air above about 40°F, and rain falling after dark. The mid-40s and warmer are treated as clearly good conditions. Programs watch for a day or two of mild weather followed by a soaking rain that lasts into the night, especially the first rainy nights of the season.

Rain matters most. In studies that counted animals at drift fences (low fences that guide animals into traps so they can be counted), rain was usually the strongest predictor of movement. If the ground dries out or the air turns much colder than 40°F, movement slows to a stop. Later in the season, a light rain, fog or simply damp ground can be enough.

The numbers differ by species and region. Wood frogs handle colder nights than spotted salamanders, western tiger salamanders move on nights above freezing, and one Florida salamander moved most around 57°F, with none caught on nights above about 72°F. Our 40°F line is a working rule from Northeast crossing programs, not a law of nature.

It is not just spring, and not just frogs

Crossing season depends on where you live, and turtles and snakes have seasons of their own. Here is what the season calendar behind this page expects right now, before any weather is taken into account.

Turtles

From late spring into midsummer, female turtles leave the water to lay eggs and often cross roads. In the North this peaks in May and June; in Florida it can start in late March. Turtles found on roads are more often female than male, and road deaths of nesting females can leave populations with too few females. Box turtles are most often seen after summer rain.

Turtle hatchlings move in late summer and fall. Some, like painted turtles, spend the winter in the nest and come out the next spring.

Snakes

Snakes travel away from winter dens in spring and back to them in fall. In Manitoba, for example, garter snakes emerge in late April or early May and return in early September; in southern Illinois a well-known “Snake Road” closes from mid-March to mid-May and again in September and October. Some snakes use roads to warm up, which puts them in danger, but scientists are not sure how often snakes seek out warm pavement.

Young amphibians

Young frogs, toads and salamanders leave their ponds in summer and early fall, often on rainy nights.

If you are driving

• Slow down at night near wetlands, ponds and woods, especially on rainy nights in your area’s crossing season.
• Watch the road surface: salamanders can look like sticks, frogs like leaves, and small frogs like pebbles.
• If one animal is crossing, others may follow.
• Some snakes freeze when a car passes, which keeps them on the road longer.
• Slow or stop only when it is safe for you and the drivers behind you. Do not swerve or brake hard for an animal.

If you want to help an animal across

Only where it is safe: help only on quiet, slow roads where you can stand well off the pavement. Never try on a busy road or where drivers cannot see you.

• Wear a reflective vest and carry a bright light; a phone light is not enough.
• Walk facing traffic, and step off the road whenever a car comes. Never dart into the road for a rescue.
• If no car is coming, you can often just let the animal finish crossing while you watch from a safe spot.
• Move the animal in the direction it was heading and set it down well off the road. If you put it back where it came from, it will try to cross again. Do not take it somewhere “better”: leave it where it was going.
• Frogs, toads and salamanders: use clean, wet hands (rainwater is fine) or clean gloves, and have nothing on your skin: no lotion, sunscreen, bug spray or hand sanitizer. Amphibians absorb chemicals through their skin. Hold them gently around the middle, never by a leg or the tail.
• Turtles: never pick a turtle up by the tail; it can injure the spine. Hold a small turtle by the sides of its shell with both hands. Leave large snapping turtles and softshell turtles alone unless you know how to move them safely: they have long necks and strong bites. Experienced helpers slide them onto a car mat or blanket, or nudge them from behind.
• Snakes: do not handle a snake unless you are sure it is harmless, and never put any part of yourself within its reach otherwise. Wildlife rehabilitators advise the public not to handle snakes at all.
• Wash your hands with soap and water afterward.
• Children should help only with an adult, one adult for each child.

Found an injured animal? Contact a licensed wildlife rehabilitator or your state or provincial wildlife agency. Do not feed it or try to treat it. Never put an injured turtle in water; rehabilitators advise a ventilated box lined with a towel, kept somewhere warm and quiet.

Join a crossing project

Many areas have volunteer crossing programs that train people, send alerts when conditions look right, and count live and dead animals. Volunteer counts have led to road closures on migration nights and to planning for wildlife passages.

Our Ways to Help finder lists the in-person, after-dark reptile and amphibian programs we know of.

Find a crossing project

Record what you see, including roadkill

Photos of animals killed on roads are useful records for scientists and road planners. Only take photos when you are safely off the road, and never while driving.

On iNaturalist (opens in a new tab), set the “Alive or Dead” annotation (opens in a new tab) (an extra label on your observation) to “Dead” for roadkill. You can also add roadkill to the GLOBAL Roadkill Observations project (opens in a new tab), run by the Road Ecology Center at UC Davis. Some states also collect crossing and roadkill reports, including Ohio (opens in a new tab), Wisconsin (opens in a new tab) and Vermont (opens in a new tab).

Laws on picking up or collecting animals from roads differ by state. In Texas (opens in a new tab), for example, taking wildlife on a public road or its right-of-way is unlawful except in narrow, licensed cases for reptiles and amphibians. Helping an animal across is not the same as collecting it, but keeping one may need a permit.

How this reading is made

This reading estimates how favorable conditions are for animals to be moving. It does not detect animals.

It combines a season calendar for your region with the National Weather Service forecast for tonight: rain after dark, the evening temperature, and whether a warm rain follows cold or dry weather (the last few weeks of weather come from NOAA’s Regional Climate Centers). Each group of animals gets a score, and the highest sets the level. Big Night is kept for the full set of triggers at the peak of the breeding season.

The temperature and rain cutoffs come mostly from long-running crossing programs in the Northeast, adjusted by region. Some are our own best judgment and will be adjusted as we learn. Even experts who forecast Big Nights by hand say they are tricky to predict, and nights that look alike can turn out very different. Animals also follow their own calendar, not just the weather.

It cannot know your local habitat, which species live near you, or your road, and it accounts for elevation only roughly. Forecasts made for one region may not fit another. When recent weather records are not available, the “after a cold or dry spell” part is left out and the reading may be low. Without a forecast (Canada for now, or when the forecast service is down), the page shows the usual level for the season, never above High, and says so.

Season calendar version 0.1.0-sci1.