Artificial floating islands for nesting Black-throated Divers Gavia arctica in Scotland:: construction, use and effect on breeding success

Sixty-three artificial floating islands (rafts) were sited at Black-throated Diver Gavia arctica territories in Scotland, the majority during 1992-95. Rafts were mainly 2.4 m x 3.6 m platforms made of polystyrene blocks on a wooden frame, covered with growing turf. Rafts were sited at lochs (lakes) where breeding success was low and/or nests had been flooded. Territory occupancy, nest site and breeding success were monitored at territories with and without rafts during 1980-97. Rafts were used at least once at 44 territories, representing about one-quarter of the national population. Most rafts were used for the first time in the first or second year of provision. At territories where they where used, rafts improved chick productivity by a factor of 2.7 (95% confidence limits: 1.3-6.2). Raft provision probably improved the chick production of the Scottish Black-throated Diver population by 44% (7-130%).