Ecotoxicological Risk and Exposure: A Comparison of Western Burrowing Owls Nesting in Agricultural and Non-Agricultural Areas in the Morley Nelson Snake River Birds of Prey National Conservation Area

In some portions of their range, western burrowing owls (Athene cunicularia hypugaea) nest in higher densities near irrigated agricultural areas when compared to non-agricultural, arid habitat. Previous research suggests that owls may associate with agricultural areas because of more reliable and abundant prey, particularly invertebrates. One potential cost of this association, however, is an increased risk of exposure of owls to pesticides that are applied to agricultural fields. I investigated the exposure to and possible effects on burrowing owls of organophosphate, organochlorine, and carbamate pesticides in the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA) located in southern Idaho. I used plasma cholinesterase as a biomarker to investigate in vivo organophosphate and carbamate exposure, footwash samples to investigate potential external exposure, and chemical analysis of whole egg contents to investigate organochlorine (p,p1-DDE) exposure in nesting adult females. I also compared eggshell thickness in agricultural and non-agricultural areas to determine the potential for thinning caused by pesticide exposure. Cholinesterase levels and eggshell thickness did not differ between owls nesting at agricultural burrows and non-agricultural burrows. Additionally, there were no pesticide residues detected in footwash samples. Therefore I found no evidence that owls nesting in agricultural areas were exposed to high levels of pesticides while breeding. However, a metabolite of dichlorodiphenyltrichloroethane (DDT), p,p1-DDE, occurred in 27 of 58 eggs sampled. Thus, despite DDT being banned from use in the United States since 1973, burrowing owls breeding in southern Idaho were exposed to residues of this organochlorine pesticide. I detected no DDT or metabolites of DDT in the soils that I sampled from areas in which owls bred in the NCA, and presence of p,p1-DDE in eggs occurred irrespective of (1) whether owls nested in agricultural or non-agricultural areas, or (2) the distance to the nearest agricultural field. Considering these results, and that organochlorine pesticides are lipid soluble and have long retention in exposed animals, it is possible that owls were exposed to p,p1-DDE during migration and/or on their wintering grounds, and not on their breeding grounds in the NCA. With one exception, p,p1-DDE concentrations in eggs in my study were lower than those known to cause reproductive impairment in other avian species. Additionally, p,p1-DDE concentrations in eggs were not correlated with eggshell thickness, so there was no evidence of the well-known eggshell thinning effects of DDT and its metabolites. These results suggest that exposure to p,p1-DDE in burrowing owls breeding in the NCA was not causing widespread reproductive impairment, regardless of where exposure may have occurred