We investigated the influence of dieldrin, a persistent organochlorine, on a top trophic level raptor, by comparing productivity and survival of Great Horned Owls (Bubo virginianus) using contaminated and uncontaminated areas. Between 1994-1996, we worked on a Superfund hazardous waste site, the Rocky Mountain Arsenal National Wildlife Refuge in Colorado. Productivity of owls did not differ between those using the contaminated and uncontaminated areas. Adults in the uncontaminated area had nominally higher survival from 15 January-15 August. Mortalities related to dieldrin in adults were most likely the result of mobilization of dieldrin from other tissues due to nutritional stress associated with reproduction. Interval survival of juveniles in contaminated and uncontaminated areas was similar, however, dieldrin residue in plasma at nine weeks of age was strongly and negatively related to survival; juveniles with higher dieldrin residues died during dispersal. Plasma dieldrin concentrations in juveniles correlated with dieldrin levels in soil and prey within parental home ranges. Consequently, sampling dieldrin in juvenile plasma is a more reliable method for monitoring the impact of dieldrin than counting number of young fledged per nest.
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Frank et al. (1999) studied this question.
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