Eradication of Norway rats for recovery of seabird habitat on Langara Island, British Columbia

Introduced Rattus norvegicus (Norway rats) caused the decline of Synthlibor amphus antiquus (ancient murrelets) and other seabirds breeding on Langara Island (approximately 3,100 ha), British Columbia. Using funds from the lit igation settlement following the Nestucca oil spill, Environment Canada era dicated Norway rats using a technique developed in New Zealand which involv ed dispensing wax baits containing the anticoagulant brodifacoum at 50 ppm from fixed bait stations. Bait stations were placed every 75 to 100 m on a grid over the entire island (1 station/ha). Rats removed bait for 26 days, after which crews placed baits in protective plastic bags in each bait stat ion. Stations loaded with baits were left on the island and rechecked four times over 2 years, after which bait stations and remaining bait were remov ed. The eradication succeeded. No signs of rats have been detected on Langa ra Island and its associated islands since January 1996. No rats were trapp ed during 1,700 trap-nights following the poison campaign. Incisor marks of rats were not found on apples or oil-dipped chew-sticks. Corvus corax (com mon ravens) likely suffered greater than 50% mortality from the eradication after apparently gaining access to the poison directly from bait stations and from scavenging rat carcasses. A monitoring and response system is bein g developed in conjunction with current users of the islands. The success o n Langara Island demonstrates how the technique proven on small New Zealand islands of less than 300 ha can be effectively extrapolated to much larger islands.