Alaska Science Center
We have some evidence indicating that contaminants may be a contributing factor in beak deformities among Black-capped Chickadees. For more information about contaminants and beak deformities, follow the links below.
| Background | Results |
Large clusters of birds with beak deformities are rare and those that have occurred have been associated with exposure to contaminants. Beginning in the 1970s, fish-eating birds in the Great Lakes region exhibited high rates of congenital deformities, including beak abnormalities. Evidence suggested that these birds were exposed to industrial sources of PCBs, PCDDs, and PCDFs (Gilbertson et al. 1991, Ludwig et al. 1996). Another cluster of deformities among aquatic birds occurred in the early 1980s in California. These deformities, including embryonic beak defects, were attributed to exposure to high concentrations of selenium from agricultural runoff (Ohlendorf et al. 1986, Hoffman et al. 1988).
Potential local sources of contaminants within southern Alaska include pesticides used in recent spruce bark beetle outbreaks, military installations in Anchorage; multiple Superfund sites; contaminated seed or suet from local suppliers; fungicides and insecticides used in agriculture; fire-retardant chemicals that have been sprayed to control several very large fires in the affected region within the past decade; and a host of other state and regional toxic release sites.
Long-distance atmospheric transport could also be a significant source of contaminants within southern Alaska and the Pacific Northwest. Persistent, semi-volatile organochlorine compounds, including agricultural pesticides and industrial pollutants such as PCBs, have been transported long distances through the atmosphere to remote regions of the earth. Atmospheric models indicate that airborne contaminants released in east Asia may reach south-central and south-east Alaska, and western Yukon Territory, British Columbia and Washington State (Blais et al. 1998, Bailey et al. 2000).
Bird species could be exposed to contaminants through direct ingestion of contaminated foods, natural or human-provided; by foraging on contaminated surfaces; through ingestion of chemicals during cavity excavation or nest building; or through inhalation of airborne contaminants.
We tested Black-capped Chickadee adults, eggs, and nestlings for contaminants, including metals and trace elements, organic pesticides, PCBs, PCDDs, and PCDFs. We found no evidence that selenium or any other element was responsible for the beak deformities, but some evidence that organochlorine compounds may be contributing factors. Adults with beak deformities had an elevated level of chromosomal damage, which was correlated with lipid level and concentrations of several organochlorine compounds. However, concentrations of these contaminants were relatively low in tissues and none is known to cause beak or keratin abnormalities. Laboratory tests for PCDDs and PCDFs, the most toxic of the organochlorine compounds, were not sensitive enough to detect potential differences between normal and deformed birds and require further study.
We also tested sunflower seeds, which are frequently used in backyard feeders, to determine if the chickadees could be exposed to contaminants through human-supplied foods. Concentrations were low in the seeds, suggesting that sunflower seeds are not a significant source of ingested contaminants.
Future research will include additional testing of affected birds for PCDD-Fs, polycyclic aromatic hydrocarbons, and emerging contaminants such as brominated compounds.