Tuesday, November 15, 2011

Deformed Black-capped Chickadee


On 14 November 2011, we banded a hatching-year, deformed Black-capped Chickadee near Dundas, Rice Co., Minnesota. I immediately recognized that this condition is similar to a situation reported in two 2010 papers published in The Auk, the journal of the American Ornithologists' Union ("Epizootic of Beak Deformities among Wild Birds in Alaska: an Emerging Disease in North America?" by MulCahy et al. [Auk 127(4):882-298, 2010) and "Beak Deformities in Northwestern Crows: Evidence of a Multispecies Epizootic" by Hemert and Handel [Auk 127(4): 746-751].) (This individual was retrapped on 28 November 2011.)

Over the past decade, Alaskan researchers have documented 2,160 Black-capped Chickadees and 435 other birds of 29 species with grossly deformed bills. High incidences of Northwestern Crow beak deformities were later reported from Vancouver, BC, and the Seattle area of Washington. Most of these birds were over 6 months old, suggesting "either a latent development or an acquired condition." The cause of this unusual concentration is unknown. Along with the beak, birds also showed lesions in other keratinized tissues of the skin, legs, feet, claws and feathers. (Note the bald areas around the eyes in my second photograph. Some feathers in my first photograph seem to be sparsely barbed).

Beak deformities are to be expected. Years ago near Aberdeen, South Dakota I photographed the Red-winged Blackbird below. Note its long lower mandible. The Alaskan researchers are alarmed at such a large cluster of abnormalities. In the 1970s, high rates of crossed mandibles were reported from aquatic birds around the Great Lakes and high levels of organochlorine contaminants were documented there. In the 1980s high levels of selenium from agricultural runoff in California produced similar effects in birds.

The beak deformities, abnormal feathers, and skin trouble suggest this situation may be a systemic keratin problem. A number of factors, including vitamin A and/or D deficiencies, might cause these symptoms. Seed-based diets are usually deficient in vitamin A and calcium. High-fat diets, common at bird feeders, can also interfere with calcium uptake. Remember, however, that the cause(s) of the Alaskan and Pacific Northwestern outbreaks remain a mystery. Hopefully this disorder is not the result of pollution or an infectious bird disease, and our deformed chickadee is just an isolated case. Birders should be on the lookout for other deformed birds.

1 comment:

  1. I'm not sure what to say...

    That's sad. How do these poor birds even live? How do they eat?

    It's awful...

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