The Displacement of Terns by Herring Gulls at the Weepecket Islands

Abstract

For over forty years Common and Roseate Terns (Steraa hirundo and Sterna dougalli) have nested at the Weepecker Islands.With an adult population of 3500 terns, this colony has been about fourth in size among the tern colonies of southern Massachusetts.Tern Island, Chatham; Ram Island, Mattapoisett; and Penikese Island are the sites of larger colonies.In some seasons the colonies at Muskeget Island, Billingsgate Island, and Egg Island, Hyannis, have been of comparable size.Since 1940 no terns have nested at the Weepeckets.In their place is a flourishing colony of Herring Gulls (Larus argentatus).This report is a description and analysis of the factors responsible for this displacement of terns by gulls.The Weepecket Islands consist of one large island and two very small ones.Large Weepecker is 1560 feet long; but at its widest only 650 feet.Its area is about 12 acres.Middle Weepecket and Outer Weepecket are much alike.Each is about 100 feet long and half as wide.The soil is the original glacial till, even on the little islands where the highest point is only 10 to 12 feet above high tide mark.In spite of rather severe erosion, accelerated by the hurricanes of 1938 and 1944, the islands retain their shape and total area.In this respect they differ from Tern Island and Muskeget where the action of storms may change conditions greatly from year to year.Large Weepecker is at lat. 4130'40" N, long.7044'30" W, lying 2000 feet north of Naushon Island in Buzzards Bay.Middlc Weepecker