NESTING RAFTS AS A MANAGEMENT TOOL FOR A DECLINING COMMON TERN (STERNA-HIRUNDO) COLONY

A Common Tern (Sterna hirundo) colony at the Eastern Headland, Toronto Outer Harbour, has been declining since 1982 due to habitat loss caused by vegetative succession and erosion, competition with Ring-billed Gulls (Larus delawarensis), predation, and human disturbances. Four wooden rafts (5 m x 5 m), covered with sand and gravel, were installed in the spring of 1990 to provide artificial nesting sites. They were provided with tern decoys, driftwood, chick shelters and ramps. Common Terns colonized the rafts and defended them against Canada Geese (Branta canadensis) and Ring-billed Gulls. Incubation began in mid-May and between 23 May to 1 June there were 115 nests and 356 eggs on the four rafts. After a storm on 3 June, we found 23 nests and 51 eggs destroyed. Between 7 June and 5 July, we recorded 128 nests and 361 eggs. A total of 170 fledglings (greater-than-or-equal-to 20 days of age) had been counted by 27 july. The mean fledgling success of pairs using the four rafts was 1.3 +/- 0.2 (xBAR +/- S.E.) fledglings per nest. Improvements to raft design are suggested.