WHY DID THE WOOD FROG CROSS THE ROAD?: To get to the temporary vernal pools where their life began. The call of spring brought the tiny creatures out of hibernation and on their journey to the vernal pools in the Sourlands. Shown here in the hands of a nature enthusiast on a Sourlands Conservancy hike, the eggs were observed by visitors after the amphibians had been helped to reach the pools last month. Each black speck surrounded by a glob of a protective jelly will likely hatch into a wood frog in about four to six weeks. (Photo by Caroline Katmann)

After March rains, visitors to the Sourland region could not have failed to notice the appearance of temporary vernal pools.

Because there are no fish in these pools, they provide a safe spot for numerous species of amphibians newly emerged from hibernation to mate and lay their eggs.

But because the pools and the places where the amphibians emerge are in many instances divided by a road, a little human help is needed to make sure creatures such as spring peepers that are less than an inch long successfully reach their destination.

This is where Caroline Katmann, executive director of the Sourlands Conservancy, County Naturalist Jenn Rogers of the Mercer County Park Commission, and volunteers step in, each year.

“During the first heavy rains when the evening temperature reaches between 40 and 50 degrees, there is an amphibian migration,” explained Ms. Katmann. “The frogs and the salamanders know instinctively when it is time to emerge from hibernation. They then follow the paths that have followed for generations to their natal vernal pools where they breed and lay their eggs. Unfortunately, over the years, roads have been built across these paths.”

The volunteer effort is part of a statewide Amphibian Crossing project by the Conserve Wildlife Foundation of New Jersey. The Sourland region is home to the spotted salamander, red-backed salamander, slimy salamander, northern two-lined salamander, northern red salamander, northern dusky salamander, jefferson salamander, american toad, fowler’s toad, spring peeper, bullfrog, green frog, wood frog, pickerel frog, and northern gray tree frog. State biologists estimate that one car passing every four minutes can potentially kill 75 percent of these species.

In some places a road might be closed in order to facilitate an amphibian crossing but on Mountain Road in East Amwell, volunteers came out to gently push or carry the amphibians across the road. As if to reward their efforts, the volunteers were treated to a spring chorus of wood frogs and peepers that had successfully reached the breeding pools to ensure another generation of their species.

Not every egg will produce an adult, however; many will be eaten as part of the food chain. According to Ms. Rogers, a large amphibian population is necessary to maintain the region’s ecosystem. Adult amphibians are meat-eaters; they control the numbers of slugs, worms, even small mammals, such as mice. In turn, the amphibians are eaten by snakes, foxes, dogs, fish, hawks, and other birds.

Last month, a recent hike to the same location by 15 participants in the Sourland Conservancy’s vernal pool walk discovered masses of shimmering flecks of gold that are the eggs of pickerel frogs, as well as wood frog eggs and spotted salamander eggs. During the walk, which was led by Ms. Rogers, participants got to check out the results of the previous month’s amphibian crossing efforts.

“Easily mistaken for lifeless bodies of water containing nothing but twigs and leaves these vernal pools are teeming with life,” said Ms. Katmann, whose personal favorite is the spotted salamander. “Seeing one was the highlight of my life; they look like they should be in the tropics.”

Free, guided hikes are a part of the Conservancy’s stewardship program. Since 1986, the Sourland Conservancy has worked to protect the ecological integrity, historic resources and special character of the Sourland Mountain region. Upcoming “Sourland Stewards Hikes,” which are limited to just 15 participants, will take place Saturday, May 16, from 9 a.m. to noon, led by Jim Amon, Sourland Conservancy Trustee and former director of Stewardship for the D&R Greenway Land Trust; and Saturday May 30, from 9 a.m. to 12:30 p.m., led by Dave Harper, former president of the Geological Association of New Jersey.

For more information, including other Sourland Conservancy-sponsored hikes, visit www.sourlandorg/stewardship. To help with the project next year, contact lcleveland@sourland.org or jrogers@mercercounty.org.

In addition, the D&R Greenway Land Trust is offering a guided tour of the Rockhopper Trail in West Amwell Saturday, May 9, from 10 a.m. Led by former D&R Greenway trustee and trail crew leader Alan Hershey, the walk is free, but space is limited and early registrations is advised. For information on other hikes by the Land Trust, call (609) 924-4646, or visit: www.drgreenway.org.