Colleen Handel, a biologist studying bill abnormalities at the United States Geological Survey's Alaska Biological Science Center, has compiled reports of deformities in 28 bird species in Alaska, including year-round residents like Black-billed Magpies, Red-breasted Nuthatches, Downy and Hairy woodpeckers, Northwestern Crows, Steller's and Gray jays, and Common Ravens. Bill deformities in migratory species, including American Tree Sparrows, Lincoln Sparrows, Ruby-crowned Kinglets, Orange-crowned Warblers, and Dark-eyed Juncos, have also been recorded. Interestingly, Handel noted, "Every migratory bird observed with a bill deformity has been a juvenile bird," meaning the birds had not yet been outside of Alaska when the deformity was observed.

For the rest of North America, she only received a total of 21 reports of chickadees with deformed bills for the same period.

Handel's team of researchers has been banding birds to track individuals. They captured 2,186 Black-capped Chickadees between 1999 and 2005. Handel and her colleagues found 178 (8.1%) of the chickadees captured to have deformed bills. By recapturing banded birds, they have determined that some birds born with normal bills later develop deformities. The youngest chickadee they captured with a bill deformity was about six months old. The bird had originally been banded in September 2001 with a normal bill. The bird was recaptured in December with an overgrown bill. When they captured the same chickadee again in February 2002, the bill had become crossed. Handel documented 54 cases in which an individual that was captured originally with a normal bill was subsequently recaptured with a deformed bill. She found that these deformities were more likely to develop during late winter than during other times of the year.

By monitoring nesting chickadees, taking blood and DNA samples, and testing for possible contaminants, Handel and her colleagues are searching for causes. The researchers monitored nests where one or both of the adults had bill deformities, but because bill deformities do not seem to show up until the birds have fledged, they found no evidence of deformity in the nestlings.

Consequently, while they have found no evidence for a genetic basis for the deformities, they still cannot rule out heredity as a possible cause.

Handel tested DNA and found that chickadees with bill deformities had a significantly greater amount of DNA damage than normal chickadees. This damage could be caused by exposure to contaminants or by disease. Handel was unable to find evidence of disease in the deformed birds.

A calcium deficiency could be causing the deformities, but no direct relationship has been proven so far. A few of the chickadees in Handel’s study had broken or deformed legs, a symptom of calcium deficiency. The short winter days in Alaska might result in an insufficient amount of Vitamin D, which would cause a reduction in the amount of calcium chickadees can absorb in winter. Furthermore, a lack of natural foods could force chickadees to become overly dependent on seeds, which, in addition to reducing the calcium intake chickadees normally get from insects, could exacerbate a calcium deficiency since the high fat content of seeds could interfere with calcium uptake in the body.

Other researchers have shown that cormorants exposed to low levels of PCB and kept in captivity for two weeks without natural daylight developed bill deformities.* The potential of a combined effect between PCBs and calcium deficiency will be tested with captive birds in the next phase of Handel’s research.

Handel and her colleagues plan to begin studying Northwestern Crows in addition to chickadees. Reports of bill deformities in these crows have been increasing, and because of their large size, contaminants may be more easily found in crows.

Handel needs the help of citizens to report every deformed bill they see anywhere in the United States or Canada. Project FeederWatch participants can help by reporting any birds they observe with deformed bills.

Learn more about Handel's research.

*Kuiken, T., G. A. Fox, and K. L. Danesik. 1999. Bill malformations in Double-crested Cormorants with low exposure to organochlorines. Environmental Toxicology and Chemistry 18:2908–2913.