During the winter of 1990 in the Fraser Delta of British Columbia, Canada, nine birds of prey were found with symptoms of anticholinesterase poisoning. Immediate surgical removal of crop contents of three birds decreased mortality and recovery time. Chemical analysis was conducted on crop contents, which contained mainly duck parts. A bald eagle (Haliaeetus leucocephalus) contained 200 micrograms/g and a red-tailed hawk (Buteo jamaicensis) 2.2 micrograms/g carbofuran, while the crop of another red-tailed hawk contained 30 micrograms/g fensulfothion. There was evidence that granular carbofuran and fensulfothion persisted long enough in the wet, low pH conditions of the Fraser Delta to kill waterfowl and cause secondary poisoning of raptors several months after application of the pesticides.