Successful restoration of the Ice Island Common Tern colony requires on-going control of Ring-billed Gulls

Ice Island, a small (0.17 ha) island in the St. Lawrence River near Mallorytown Landing, Ontario, Canada, supported 121 nests of Common Terns (Sterna hirundo) in 1976. By 1989 the island had been completely taken over by 181 pairs of nesting Ring-billed Gulls (Larus delawarensis). During the 1990-1993 breeding seasons, the tern colony was gradually restored by excluding gulls through the installation of monofilament lines, the repeated removal of gull nests, and the placement of wooden tern decoys. Tern nest numbers increased from 2 in 1990 to 135 in 1993. During the 1994-1996 breeding seasons, no lines were installed and not all gull nests were removed. During this 3-year period, the number of Ring-billed Gull nests increased from 2 in 1994 to approx. 250 in 1996, while the number of Common Tern nests first continued to increase to 149 in 1995, but then steeply declined to 3 in 1996. On-going gull control is required to main rain the Ice Island tern colony.