Owls as biomonitors of environmental contamination

Much like the caged canary used by miners, a plethora of wildlife species have been promoted as biomonitors of environmental contamination. These species provide an "early warning system" for toxic contaminants in the environment. Species promoted as useful biomonitors share many common life history characters, such as wide distribution, territorial, non-migratory behavior, high trophic status, and high reproductive rates. Raptor species generally possess these characteristics. The Bald Eagle (Haliaeetus leucocephalus) and Osprey (Pandion haliaetus) have been widely used as biomonitors of aquatic contamination. However, few higher order consumers have been studied in detail or proposed for use in terrestrial systems. Exposure and effects of environmental contaminants on owls has been largely understudied. The studies done to date on owls and environmental contaminants have been conducted on both captive and wild owls, and have focused on a few selected species. Most of the captive studies have been conducted using Eastern Screech-owl (Otus asio) and Barn Owl (Tyto alba) colonies at the USFWS Patuxent Wildlife Research Center, Laurel, MD. The relatively few studies conducted on wild owls have included many different species, but have concentrated on the Great Horned Owl (Bubo virginianus), Barn Owl, and Eastern Screech-owl, and have focused heavily on analyzing contaminant levels (residue analyses) and post-mortem examination for cause of death of individual owls found dead. As higher order consumers, owls are susceptible to secondary poisoning and can bioconcentrate many different environmental contaminants through their prey. Owls have proven to be sensitive to a wide variety of toxic compounds, including pesticides, PCB's, metals, and fluoride, and are highly susceptible to secondary poisoning from consuming pesticide-poisoned prey. Endpoints examined include reproductive effects, eggshell thickness, residue analyses, cholinesterase inhibition, and induction of liver detoxifying enzymes. Much more work remains to be done using owls as biomonitors of environmental contamination, particularly with captive populations, salvaged individuals, raptor rehabilitation center birds, and with wild populations in areas around hazardous waste sites, smelters, landfills, agricultural croplands, and other major sources of environmental contamination.