Ospreys are once again harbingers of spring across Chesapeake Bay, thanks largely to regulation of DDT and other pesticides that had devastated the species’ population during the mid-1900s. But the emergence of new environmental contaminants, including flame-retardant compounds known as PBDEs, is raising concern among scientists who study the birds.
VIMS Professor Dr. Rob Hale, a leading authority on the behavior of PBDEs in the environment, is collaborating with avian experts from around Chesapeake Bay to determine the exposure of osprey to these new contaminants, and to traditional pollutants such as DDT, PCBs, and mercury. Hale’s collaborators include Research Associate Reese Lukei of the Center for Conservation Biology (CCB) at William & Mary, as well as scientists at the Patuxent Wildlife Research Center, the U.S. Fish and Wildlife Service, the University of Maryland, and the U.S. Department of Agriculture.
Results of their research appear in the latest issue of the Archives of Environmental Contamination and Toxicology. Hale is also teaming with CCB and W&M undergraduate Catherine Potter to study the effects of PBDEs on peregrine falcons. Because peregrines feed on other birds of prey from their perch atop the food web, researchers suspect they may be especially likely to concentrate contaminants in their tissues.
Hale’s role in the osprey study was to analyze PBDE levels in eggs taken from nests along the Elizabeth River, Baltimore Harbor, and the Anacostia, Patapsco, and mid-Potomac rivers. These are some of the most highly polluted areas of Chesapeake Bay. The researchers removed a single egg from nests in these sites and compared their contaminant levels with eggs taken from nests along tributaries thought to be largely contaminant-free (a typical osprey nest contains 3 eggs).
They also followed the fate of the remaining eggs until they hatched and the chicks fledged. Ospreys in all but one of the contaminated sites showed only marginal success in breeding. Nests in the Elizabeth River and the pristine sites were sufficiently productive to maintain the local population. Analysis of eggs from the contaminated sites showed that they often contained higher concentrations of PBDEs, PCBs, and DDE (a breakdown product of DDT) than eggs from the pristine sites. There was, however, no clear statistical correlation between individual contaminant concentrations and nesting success.
“There are likely additional factors at play that preclude a simple correlation between contamination levels and nesting problems,” says Hale. “There may be other contaminants that we didn’t sample for, or some of our known contaminants may have already been transformed by organisms and eliminated. Habitat loss probably also plays a role.”
The migratory nature of many of the osprey’s fishy prey, together with the bird’s extensive hunting range, may also help explain the lack of a clear correlation. Most troubling, notes Hale, is that PBDE concentrations appear to be increasing in the osprey population. Levels are now 4 times higher in the Anacostia and Potomac rivers than in pristine sites.
Previous laboratory studies by Hale and graduate student Mark La Guardia show that exposure to PBDEs can alter reproduction and nervous system development in many organisms.