The Effects of Ditching a Salt Marsh on Colony and Nest Site Selection by Herring Gulls (Larus argentatus)

Abstract

Herring gulls recently invaded and now nest on salt marsh islands in New Jersey. In 1971 about 50 pairs nested in an area of Spartina patens that contained a few Iva bushes on Sandy Island. In 1972 one half of the island containing the herring gull colony was ditched with internal ditches connected to the surrounding bay, and the other half of the island was ditched only internally. Although in 1971 the vegetation on both sub-islands was similar (primarily Spartina), the sub-island with ditches connected to tidal areas underwent major changes as bushes moved into over 80% of the area. No significant vegetational changes occurred on the sub-island with only internal ditching, and the gulls moved to this area. Gulls nested in Spartina patens, on spoil piles near bushes. As the highest in the marsh, these areas are thus less susceptible to storm and flood tides. The gulls nesting on spoils built higher nests, laid bigger eggs, and had a higher mean clutch size than birds that did not nest on spoil piles. This suggests that spoil piles are the preferred habitat of the older, more experienced birds. We discuss the nesting behavior of the gulls in terms of the vegetational changes coused by different methods of ditching.