Orchard dormant sprays and exposure of red-tailed hawks to organophosphates

A pilot study of raptors live-trapped in the Central Valley of California suggested that they were being exposed to organophosphate insecticides (OPs) in winter dormant-season sprays (Hooper et al., 1989). Eight of 12 raptors trapped in the vicinity of orchards in Butte County had low blood cholinesterase (ChE); 4 responded to oxime reactivation, and OP metabolites were found in their excreta. This paper presents preliminary results of an enlarged study from a large number of hawks live-trapped in the Sacramento and San Joaquin Valleys of California during the winter of 1987-88. ChE levels of birds from rehabilitation centers and from hawks kept at the University of California, Davis (UCD) Raptor Center are also reported.