HAMPTON -- Birdwatchers in salt marshes are heralding the arrival of a lesser known harbinger of spring: the greater yellowlegs.

Greater yellowlegs (Tringa melanoleuca) is one of more than two dozen shorebird species that use local marshes to rest and replenish fat reserves on their annual migrations. The rather large sandpiper sports long bright yellow legs, a long bill and a conspicuous white rump. Most yellowlegs that visit the Hampton area are heading north to breed throughout the boreal forest of Canada.

The N.H. Audubon Society and its research partners are especially interested in the presence of greater yellowlegs and other shorebirds because they reveal information about the entire ecosystem. The same food items eaten by shorebirds are ultimately important to many other marine animals, including the fish that sustain the region's commercial and recreational fisheries.

To study bird distribution in salt marshes, N.H. Audubon launched a volunteer-driven program to document feeding areas across the salt marsh habitat. The 2007 field season focuses on why some areas of the estuary are used selectively over others by shorebirds. The answer will provide insight on the marine invertebrate prey base and water and substrate quality.

In addition to providing ecological information, the Hampton-Seabrook estuary study will help the community identify and implement restoration and conservation projects. Once the natural function of an area is restored, the benefits can be enjoyed by both birds and people.

Peter McKinley is the N.H. Audubon Seacoast biologist. Eye on our Estuaries is an educational column initiated by the New Hampshire Estuaries Project about coastal watershed issues. For information, visit www.nhep.unh.edu.