As I mentioned in my previous post, Northwestern Crow populations have shown a strong overall increase over the past half century, despite a 4% (BC Conservation Data Centre, 2015) decline in BC and Alaskan records over the past 2 decades. The crow populations appear superficially healthy, however there may be an emerging reason for concern. In Alaska, and further south, beak deformity has been recorded at rates significantly higher than ever previously observed in a wild bird population (Van Hemert and Handel, 2010). This suggests a possible epizootic, equivalent to an epidemic in humans. This epizootic of beak deformities may be a warning that this seemingly robust bird may be more vulnerable in its environment than it’s adaptive behaviour might suggest, or there has been a marked change in the ecosystem (Handel et al., 2010).
In Alaska, government scientists have been studying native bird populations to learn more about the beak deformities. Normally bill deformities are not prevalent within populations (Van Hemert and Handel, 2010). High incidents of beak deformity in wild bird populations can point to environmental problems (Handel et al., 2010) (Van Hemert and Handel, 2010). Through her research on Black-capped Chickadees (Poecile atricapillus), Alaskan scientist Colleen Handel was alerted to a few birds with deformed bills showing up at bird feeders in the late 1990’s. Handel requested public help in documenting occurrences of beak deformities in chickadees at bird feeders and received numerous accounts about other birds, including a considerable number of Northwestern Crows with beak deformities, many of them south of Alaska. Beak elongation affected either the top and bottom beak or both beaks at the same time and frequently resulted in the bird having difficulty feeding and grooming (Kay, 2014). The abnormalities of the two avian species was found to be a result of avian keratin disorder, a condition that occurs when the outer keratinized layer on the beak becomes grossly overgrown (Van Hemert et al., 2012). The parallel condition led to a study on the prevalence and morphological extent of beak deformities in crows and the geographic range of occurrences (Van Hemert and Handel, 2010).
Handel and her research partner Caroline Van Hemert sampled crow populations at six coastal sites in Alaska for 1 year between 2007 and 2008. Each site was near a human settlement and provided a mixture of natural and human generated food available to the crows (Van Hemert and Handel, 2010). They measured 186 crows and found 19 adults with beaks classified as deformed and no juveniles with the deformity. The overall level of deformities exceeded their expectations by over 30 times. The prevalence of beak deformity in the crows was as much as 17%, much higher than the 6.5% found in the chickadees (Van Hemert and Handel, 2010). At two of the sites with greater occurrences of deformities, eight other species of birds displayed beak deformities. These two locations were also in close proximity to where the highest occurrences of beak deformity were noted in chickadees. Through a review of literature and observations compiled since 1980, 148 crows were found to have beak deformities, most of them since 1997. Sixty-four reports came from BC and Washington of crows with abnormal beaks. Only five observations were recorded from the rest of North America. This clear prevalence of occurrences since 1997 is equivalent to that of Black-capped Chickadees (Van Hemert and Handel, 2010).
While no conclusions have yet been drawn, the authors have suspected both viruses and environmental contaminants and point out possible clues and directions for future research. They suggest the deformities are unlikely to be caused by parasites or infectious disease, because these localized avian populations are not exposed to transient agents. They suggest that because of the overwhelming similarity of characteristics there is some factor ‘unique to the region’ causing the same disorder in crows as in all the birds studied. If it is an environmental factor or contamination then it would be diffuse because of the large geographic range of occurrences and more specific testing is necessary. Further studies of crows living away from human habitation would provide useful comparison. Further research into the pathology of avian keratin disorder may also be helpful in isolating the cause.
References for blog posts 1 & 2:
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Ward M., 2013, Crows Over Commercial Drive, Vancouver (video) https://www.youtube.com/watch?v=sgmdW_Uut1U (Oct 27 2015)