CHRONIC ORGANOCHLORINE CONTAMINANTS, ENVIRONMENTAL VARIABILITY, AND THE DEMOGRAPHICS OF A BURROWING OWL POPULATION

Abstract

We studied a population of Burrowing Owls whose eggs contained the organochlorine compound p,p′DDE and traces of other organochlorine contaminants to determine if the levels of contamination were associated with survival or reproduction when nonanthropogenic environmental and biological variables were also considered. Demographic data were collected in conjunction with sampling eggs for contaminants and analyzing pellets for dietary information. Levels of p,p′DDE in eggs varied over four orders of magnitude during the study but were not by themselves associated with reproductive failure. However, contaminant concentrations in combination with low rodent abundance in the diet were related to reduced productivity. The variation within and among years in egg contaminants suggests that patterns of egg contaminants are the result of immigrating owls from more contaminated sites, and to a lesser extent, to annual patterns in prey availability. Even low levels of chronic pesticide exposure may be detrimental when combined with other stressors, and documentation of the existence of a persistent pesticide in a biotic system is not enough to either infer the origin of the contamination or its potential effects.