CASPIAN TERNS (STERNA-CASPIA) BREED SUCCESSFULLY ON A NESTING RAFT

The Caspian Tern (Sterna caspia) occurs in Ontario on Lake Ontario and Lake Huron, where is provincial status is rare. The colony at Hamilto n Harbour is one of five Lake Ontario colonies, but its present locati on within the harbor is threatened by development plans. In an effort to determine the feasibility of relocating Caspian Terns, a raft was b uilt and installed as an alternative nesting site during the 1993-1995 breeding seasons. In 1993, one pair established a nest and raised two chicks to at least 25 days, in 1994, six pairs nested and six chicks fledged and in 1995, 50 pairs nested and raised 97 chicks to fledging. In 1993, colonization of the raft by one pair occurred within 11 days of removal of a tarpaulin put in place to discourage nesting by gulls . In 1994, the raft was not colonized until late in the breeding seaso n, some 42 days after it became available. Factors influencing the lat e nesting in 1994 are unclear, but may relate to either a renesting of failed pairs from mainland sites, or a loss of habitat in the mainlan d sub-colonies due to encroachment by Ring-billed Gulls (Larus delawar ensis) and increasing vegetation. In 1995, the raft was colonized by 8 May and at least 50 pairs nested, raising approximately two young per nest. Heavy predation by red fox (Vulpes vulpes) on mainland sub-colo nies resulted in the raft providing the majority of fledged young in 1 995.