CONCORD, N.H. (AP) — Northern New England’s annual amphibian migration is always perilous, but critters that cross roads to breed are facing an additional challenge this year: a delayed start after the long winter.

Every spring, several species of salamanders and frogs travel to vernal pools — temporary bodies of water created by melted snow — to mate and lay eggs, and the resulting offspring need several months to develop and grow legs before the pools dry up in summer. Wildlife officials say the migration is running a week or two behind this year, cutting into that critical development time.

That could affect millions of animals across Vermont, Maine and New Hampshire, said Eric Orff, a wildlife biologist with the National Wildlife Federation.

“With a late spring and climate change predicting hotter, drier summers, we’re really in a race against time before these vernal pools dry up, leaving these animals stranded to die,” he said.

Mike Marchand, a wildlife biologist with New Hampshire Fish and Game, said the state is home to five species that depend solely on vernal pools: the wood frog and four types of salamanders, including one that is endangered in the state and two that are “of conservation concern.” All serve key ecosystem roles — salamanders eat mosquito larvae, and the frogs are an important food source for other animals at all stages of their development, he said.

The critters start moving on rainy nights when temperatures are in the 40s and 50s, and officials are urging residents to do what they can to help the amphibians survive their trek.

“If you can get that gallon of milk on the way home from work and avoid driving when rain is predicted after dark, that’s the best thing — to stay off the road if you can,” Orff said. “If you must drive when it’s raining at night, slow down. Slow way down, and think ‘frog.'”

In southwestern New Hampshire, last Monday was what those in the know call “Big Night,” — the season’s first significant migration. Nearly 100 volunteers took to the streets, shuttling nearly 3,000 amphibians across the road. Wearing reflective vests and holding flashlights, they scooped up spring peepers, wood frogs and salamanders and carried them either in their hands or buckets, then documented each find.

The Harris Center for Conservation Education has been training volunteers for its “Salamander Crossing Brigades” since 2007, and more recently has begun photographing the markings on yellow spotted salamanders, said program director Brett Thelen. Amphibians tend to return to the pools where they were born to breed, and the photos helped confirm that several of the salamanders that were helped on Monday were repeat travelers, she said.

Volunteers also count the critters that end up as road kill, though the focus is on the living, Thelen said. Most of the dead amphibians get scavenged by other animals or are “pulverized beyond recognition” within hours, she said.

“If you’re driving the roads in the middle of the night on a migration night, you will see the dead, but by morning, you won’t know that it happened,” she said. “It’s not like a deer or a raccoon that will stay on the road for a long time.”

Thelen acknowledges that asking people to avoid driving on rainy nights sounds ridiculous, but she hopes they will at least slow down and witness the migration.

“It’s an incredible, incredible spring phenomenon,” she said. “It’s a magical time when all of these animals who spend most of their lives underground out of sight are emerging.”

Orff agrees.

“Really, in the next few weeks New Hampshire will have more life than any other time of year, with all these frogs and salamanders hatching into tadpoles,” he said. “It brings life to New Hampshire’s forests.”