The sign said the road was closed, but a fisherman told us it might be passable. Trusting his local knowledge, we drove around the warning sign.

Violent spring weather has washed out some of these little-used coastal back roads. The berm was badly eroded, and storm-tossed flotsam was scattered across the road. Concrete construction debris was dumped in an attempt to stabilize the shoreline. A faint scrim of pebble and sparse sand obscured the water's edge.

This unlikely beach was our destination. Pat gingerly inched the car to the side of the uncertain road. Ruddy turnstones, semipalmated sandpipers and dunlins were here by the hundreds. Laughing gulls and ring-billed gulls added a noisy soundtrack to the feeding frenzy. Out of the car, we spot the real reason for our trek across the Delmarva-a shorebird with a brick-red breast.

The red knot (Calidris canutus) is the largest of the sandpipers called peeps. The robin-size bird weighs almost 5 ounces. Its bill and legs are relatively short, stocky and black. The red knot gets its name from the salmon-hued breeding plumage on its head, neck and breast. Its back is gray and the underside white. Although these are handsome birds, they are visually less arresting than the calico-colored turnstones inches away.

Red knots live on every continent except Antarctica. They winter in isolated spots from California and Massachusetts down to the tip of South America. Small numbers can be found along the Maryland and Virginia shoreline. What makes these birds remarkable is the subspecies rufa.

This race of red knots breeds a thousand miles north of the Arctic Circle. It spends its winters half a world away along the coasts of Patagonia. These birds make the 9,000-mile trip annually, and this rubble-strewn beach plays a key role in that migration.

Every April, the red knots of Tierra del Fuego work their way up the Argentine coast, congregating in southernmost Brazil. There, they eat prodigious amounts of snails and shellfish, amassing strength for the journey ahead.

The red knots, bulging with stores of energy, then take to the wing. They fly for the next week non-stop-an estimated 130-190 hours of flying without rest.

For many, the route is a 7,000-mile arc that takes them around the bulge of Brazil and then directly here to the shores of the Delaware Bay. The birds arrive emaciated and exhausted from their marathon flight.

Their arrival coincides with the spawning of the horseshoe crab. These prehistoric creatures predate the dinosaurs and are more closely related to spiders than crabs. A dinner plate-size gray carapace and 8-inch spiky tail give them an alien appearance.

Red knots and horseshoe crabs have parallel migration patterns. The ancient crab's trip is arduous, but pedestrian.

They slowly scuffle from the edge of the continental shelf and out of the depths of the Delaware Bay to procreate on these hardscrabble beaches. The breeding peaks with the high tides that accompany the last full moon of May.

A female can grow to 2 feet, and biologists estimate that she can lay as many as 80,000 tapioca-size, greenish eggs every season. This extraordinary productivity is necessary. Only a tiny fraction of the eggs will be fertilized and fewer still will survive to maturity.

For the red knots, too, the eggs are essential. The birds need to recover from their journey. For two weeks they will restore themselves and prepare for the last leg of their journey. It is still 2,000 miles to their breeding grounds. The eggs must exist in quantities that defy the imagination. Two species' survival hangs in the balance.

Since the mid-1980s, the South American red knot population has dropped by more than half. A sudden burst of commercial harvesting of the horseshoe crabs for use as bait is generally blamed for the steep drop. Even a casual observer like me has seen the decline. Recent fishery restrictions imposed by coastal states may slow the trend.

Less plentiful than before, the eggs are still present in staggering numbers. From yards away, the beach glistens green and globular. As the tide continues to come in, more shorebirds and gulls join the fray. The beach is seething now with thousands of birds and crabs. We watch for hours.

Sitting on a boulder with so many birds in easy view, I try to comprehend the scene. The impossible is a daily occurrence in the natural world. We are witness to an annual miracle of timing, fecundity and strength. Unfathomable flights and endless eggs have converged in this most unlikely place.

In spite of all the signs to the contrary, it appears that the way here remains open, at least for a time.