Environmental Contaminants and Beak Deformities in Alaskan Chickadees

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A recent study by the U.S. Geological Survey (USGS) provides some of the first environmental contaminants data for a species of passerine bird (perching birds) in Alaska but leaves unanswered questions as to the cause of beak abnormalities found in this species.Beginning in the late 1990s, biologists and members of the public reported an unusual number of beak abnormalities among black-capped chickadees (Poecile atricapillus) in south-central Alaska. The frequency and distribution of observations increased during the ensuing decade, and subsequent studies have since revealed the highest rates of gross abnormalities reported in a wild bird population. To determine if environmental contaminants might be associated with beak deformities in Alaska, the USGS tested for a broad suite of inorganic and organic compounds in the tissues of affected and unaffected adult chickadees, their nestlings, and their eggs.

Small bird with crossed beak

Typical beak deformity in a black-capped chickadee (Poecile atricapillus) affected by avian keratin disorder in Anchorage, Alaska. Photo credit: Colleen Handel, USGS.

Results from toxicological analyses did not point to any individual compoundas a cause for the beak abnormalities in chickadees; however, affected birds had elevated levels of chromosomal damage, a biomarker that has been associated with exposure to environmental contaminants in other species. In addition, strong correlations between levels of chromosomal damage, and lipid concentrations of select organochlorine pesticides (such as dichlorodiphenyldichloroethylene [DDE]) suggest a possible relation between beak abnormalities and exposure to lipophilic contaminants. Further analyses of additional compounds, including polycyclic aromatic hydrocarbons, polychlorinated dibenzo-dioxins and polychlorinated dibenzofurans, and brominated flame retardants, are necessary to answer outstanding questions about the role of environmental contaminants in the development of beak deformities in black-capped chickadees. Although generally detected at low concentrations, organochlorine compounds were detected in chickadees at all life stages.

Chickadees are nonmigratory and have small home ranges, which indicates that the contaminants detected in the tissues of these birds are present in the local environment. This study provides contaminant data for a terrestrial passerine in North America and offers important baseline information for birds in Alaska.

This study was funded by the USGS Wildlife: Terrestrial and Endangered Resources and Contaminant Biology Programs and the U.S. Fish and Wildlife Service Environmental Contaminants Program.