Burrowing owls and agricultural pesticides: Evaluation of residues and risks for three populations in California, USA

We examined selenium, organophosphorus, and organochlorine pesticide residues in egg, footwash, and feather samples from burrowing owls in three populations in central and southern California. Eggs from ail sites contained detectable levels of p,p'-dichlorodiphenyldichloroethylene, with the San Joaquin Valley site containing up to 33 mu g/g (geometric mean (x) over bar = 7.52). Only low levels of polychlorinated biphenyls were detected, however (geometric mean (x) over bar = 1.98, n = 2). Selenuim concentrations were low in all samples (geometric mean (x) over bar = 0.426, n = 20). Eggshells collected in 1996 were 22% thinner than eggs collected prior to 1937. In addition, feather samples contained low levels of dichlorodiphenyldichloroethylene, and footwash samples indicated exposure to the pesticide chlorpyrifos. Pesticide-use records indicated that one population might also be at risk from applications of aldicarb near nests during the breeding season.