The red listed eagle owl (Bubo bubo) population in Norway is exposed to POP levels exceeding threshold values for adverse health effects

The eagle owl (Bubo bubo) population in Norway is today classified as critically endangered on the red list of endangered species. Because previous studies have detected high concentrations of Persistent Organic Pollutants (POPs) in birds of prey, concerns have been raised whether POPs exposure are a significant factor to the substantial decline of the eagle owl population.The aims of this study were to measure the levels of POPs in eagle owls and to assess whether POPs may represent a potential health risk. POPs were analysed in liver samples from 100 eagle owls collected between 1994 and 2014.The concentrations of POPs were generally very high and individual birds had levels among the highest measured worldwide. The contaminant groups analysed were highly correlated (p < 0.0001). The concentrations of sum of Polychlorinated Biphenyls (∑PCB) exceeded the threshold value from moderate to severe health risk in 90% of the birds. The birds with cachectic or lean body condition had significantly higher levels of contaminants than those with higher body condition scores. No significant temporal or spatial trends were noted.The lack of temporal trends, suggest that the downward trend of POPs, appear to be levelling off. The lack of differences between inland and coastal regions suggest that the risk of exposure may be comparable between predatory birds feeding in marine or terrestrial food webs. The significantly higher POPs levels detected in individuals with poor body condition may be due to reduced fat stores and thereby higher concentration in the remaining fat and/or the weight loss could be induced by toxic effects. The high proportion of birds exceeding the threshold values for severe and high risk of adverse effects, suggest that the high contamination load may reduce the eagle owl’s fitness and survival and, thus, contribute to decline of the eagle owl population.