Roberto Borea, Associated Press The notches visible on both sides of the rear of the diamondback hatchling's shell are marks made by the researchers to designate it as having been born on Poplar Island in Chesapeake Bay.

Timing is everything. Visit the New Jersey shore before Memorial Day or after mid-July and you'll never see a diamondback terrapin.

These aquatic turtles spend most of the year in the streams and salt marshes between the mainland and the barrier beach islands along the East Coast south of Cape Cod. But for about six weeks in June and early July, females leave the marsh to dig nests above the high tide line and lay eggs.

Invariably and unerringly, they head for the barrier islands, which today are home to popular resort communities such as Avalon and Stone Harbor. On June 25, our first day at the beach this year, Sea Isle City teemed with terrapins. Dozens lumbered across streets and along sidewalks.

Their destinations were "lawns" landscaped with beach gravel. I observed one female, about the size of a dinner plate, just as she reached her nesting site.

Initially, she seemed to wander aimlessly about the yard. Then, for reasons known only to her, she selected a spot and began to dig with her hind legs. Working blindly, her broad paddle-like feet shoveled alternately to sweep a small area free of gravel. When she reached the compact sandy subsurface, the task got more difficult. Each swipe of a leg threw out a scoop of sand. Her effort reminded me of a two-armed backhoe. She continued relentlessly for about 15 minutes. The completed nest was flask-shaped -- wider at the bottom than the top -- and as deep as her legs could reach.

As I watched from 20 feet away so I wouldn't disturb her, she began laying eggs. In just a few minutes, she laid nine white, oblong eggs.

When the final egg dropped, she immediately began to backfill the nest chamber. After returning the excavated sand, she reached widely to pull in stones to cover the nest. The entire ritual lasted about 30 minutes.

When the nest was complete, the female headed back to the salt marsh. In 16-17 days, she will return to the same area to nest again. Most females produce two or three clutches during the six-week nesting season. The eggs, warmed by the sun, hatch in six to seven weeks. Some quarter-sized hatchlings emerge by late summer and head to the marsh; others overwinter in the nest and emerge the following spring.

Roger Wood, director of research at the Wetlands Institute (www.wetlandsinstitute.org) in Stone Harbor, calls the hatchlings "sea gull potato chips" because gulls, crows, crabs and other predators gobble them up. Wood estimates that only one in 100 hatchlings survive to adulthood.

High predation combined with the hundreds of road-killed pregnant females make terrapin life a struggle. In fact, that's what motivated Wood to get involved. He got tired of seeing hatchlings eaten by gulls and adult females smashed by cars. Through July 3, volunteers already had picked up 273 road-killed females this year.

For 19 years Wood has assembled a growing team of volunteers, interns and colleagues to help the turtles. They have developed a turtle excluder device that keeps most terrapins out of deadly submerged crab traps. They maintain "turtle patrols" during the nesting season to rescue females crossing busy roads. And in 2004 they began erecting "turtle fences" along the causeways to keep terrapins off the roads. This alone led to an 85 percent reduction in mortality along the causeway leading to Stone Harbor.

Terrapin conservation also includes an innovative "head start" program. Volunteers collect road-killed females, remove the eggs, and incubate them in captivity. Incubation temperature determines the sex of turtles, so all head-started individuals are reared to become females and thus replace their dead mothers.

Furthermore, head-start terrapins are kept active and well fed all winter, so one year after hatching they attain a size (about 3.5 inches) that takes four or five years in nature. Head-starters 1 year old can then be released with a greatly reduced risk of predation.

Ultimately, however, the fate of diamondback terrapins rests with educating the vacationing public. Understanding terrapin biology is the first giant step.