there shelter salamanders and spadefoot toads. The native salt-water marshes between Plum Island and the mainland (Great Marsh) are visible from the western edge of the island. Salt marsh hay which grows there has been harvested for feeding farm animals. Less visible in "the low marsh" at the margin of the water is smooth cordgrass. Also in the marsh are the sedges, Cyperus and Carex. In the 1940s and '50s the wildlife service created two freshwater marshes, North and South Pools, from island runoff by diking a section of the marsh contiguous to the island. It serves as a nesting area and stopover for migrating birds. Originally the common cattail dominated the freshwater marshes, but two intrusive plants, the common reed and purple loosestrife, have replaced much of it. Mammals The mammals are typical of Massachusetts woodland: the striped skunk, the raccoon, the red fox, the meadow jumping mouse, the white-tailed deer, meadow vole, white-footed mouse and others. Avians Plum Island and its surrounding estuaries are a popular destination for birders. Plum Island Sound is on a migratory route for many varieties of birds, as well as being a nesting area for piping plovers. Much of the beach in the National Wildlife Refuge is closed to visitors during the nesting season, which can last most of the warm months. Several prepared observation posts of birds are usually populated by birders with equipment ranging from simple binoculars to expensive telephoto cameras. Some posts are blinds; others are simply a paved shoulder with a sign. Birds are usually observed in the native salt-water marshes, the artificial fresh-water marshes and the thickets and isolated trees of the refuge. The birds most commonly observed are listed in the visitor center in the refuge. They are the greater yellowlegs, mallard duck, least sandpiper, great egret, snowy egret, herring gull, great black-backed gull, osprey, Canada goose, tree swallow, gray catbird, killdeer, glossy ibis, red-winged blackbird, northern mockingbird, least tern, piping plover and peregrine falcon. Beach and dune pests Greenhead flies The greatest visible pest to humans is the greenhead fly. Before insect control they swarmed the beach and dunes so thickly as to make human presence there difficult if not impossible from June through September. In recent years the near elimination of the population with traps has reduced their impact to an occasional bite. Ticks The dog tick and the deer tick enter the clothing of