The introduction of rat species (Rattus spp.) is a conservation concern for island avifauna throughout the world. I employed 3 commonly used monitoring techniques for rats: live-trapping, snap-trapping, and apples as indicator baits at several sites on Langara Island, British Columbia, with and without the presence of breeding seabirds. Capture rates of Norway rats (Rattus norvegicus) in snap traps in an ancient murrelet (Synthliboramphus antiquus) colony while murrelets were actively breeding ranged between 0.0 and 0.7 captures per 100 trap-nights (C/100 TN), while concurrent capture rates in other regions of the island outside of the ancient murrelet colony ranged from 2.2 to 17.1 C/100 TN. Live traps in the ancient murrelet colony also had low capture rates (0 to 0.5 C/100 TN) while murrelets were present in the colony. Once murrelets departed following their breeding, capture rates in snap traps in the ancient murrelet colony rose to 9.9 to 14.0 C/100TN, rates comparable to other areas of the island without breeding seabirds. Apples were a useful monitoring tool and detected the presence of rats in seabird-nesting areas where no rats were trapped with snap or live traps. I conclude that the presence of breeding seabirds undermines the utility of traps as monitoring tools and that research and management efforts dependent on the capture of rats would best be carried out before or after the breeding season of these seabirds.
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