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Other types of beak deformities have been attributed to parasites or disease, such as psittacine beak and feather disease. However, laboratory examination and testing of deformed Black-capped Chickadees did not find evidence of disease or parasites.
Overgrowth of the beak can be a symptom of liver disease (Harrison 1986). Necropsy and histopathology of deformed chickadees did not reveal any abnormal pathology of internal organs, including liver, spleen, and thyroid. Blood serum biochemistry did not indicate that deformed chickadees were responding to any type of infection. There was no evidence of infection with the parasitic scaly mite Cnemidocoptes pilae,which can cause lesions on the beak. Tests were negative for both avian polyomavirus and the circovirus that causes psittacine beak and feather disease, which is not currently known to infect passerine birds (Tully et al. 2000) |
