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 (Van Hemert and Handel, 2010) 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, 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 (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:

Emery N.J, Clayton N.S. 2004 The Mentality of Crows: Convergent Evolution of Intelligence in Corvids and Apes Science V.302, pp.1903-1907   http://www.sciencemag.org/content/306/5703/1903.abstract?sid=e39eb11f-f3eb-47ff-80f3-0a2ada1b9c4b

Vancouver Avian Research Centre, Species: Northwestern Crow Corvus caurinus http://www.birdvancouver.com/b_northwestern_crow.html  (Oct. 27 2015)

Brewer et al., Canadian Atlas of Bird Banding,  2006, Volume 1: Doves, Cuckoos, and Hummingbirds through Passerines 2nd edition, 1921–1995 http://www.ec.gc.ca/aobc-cabb/index.aspx?lang=En&nav=bird_oiseaux&aou=489

Sibley A.S., 2003, The Sibley Field Guide To Birds of Western North America, A.A Knopf, New York, p.308

Tweit B. 2015, E-Bird Northwest News and Features, Northwestern Crows, Genetics, and eBird: New Science for an Old Problem http://ebird.org/content/nw/news/northwestern-crows-genetics-and-ebird-new-science-for-an-old-problem/ (Oct. 27 2015)

Cornell University, 2015, All About Birds-Bird Guide Northwestern Crow, Life History, http://www.allaboutbirds.org/guide/Northwestern_Crow/lifehistory (Oct. 31, 2015)

Marzluff J.M., Angell T.,2008, In the Company of Crows and Ravens, Yale University Press, p. unavailable https://books.google.ca/books?id=Bc5YO5PnPmMC&pg=PT244&lpg=PT244&dq=In+the+company+of+crows+and+ravens+mcdonalds&source=bl&ots=ONLek6aA6o&sig=Jf20d0ckm-XyxKE51omzjtfy0VI&hl=en&sa=X&ved=0CDAQ6AEwAWoVChMIne61wJHyyAIVxDKICh2VWwo2#v=onepage&q=In%20the%20company%20of%20crows%20and%20ravens%20mcdonalds&f=false

Link R., 2005, Washington Department of Fish and Wildlife, Living With Wildlife, Crows,  http://wdfw.wa.gov/living/crows.html (Oct.31, 2015)

Ehrlich P.R., Dobkin D.S., Wheye D., 1988, The Birder’s Handbook, A Field Guide to the Natural History of North American Birds, Simon and Schuster, New York, p.416.

Gullison, D. 2015, Northwestern Crow Call, (sound recording), Nanaimo, Canada.

Ward M., 2013, Crows Over Commercial Drive, Vancouver (video)  https://www.youtube.com/watch?v=sgmdW_Uut1U (Oct. 27, 2015)

Campbell W., Smith G.E.J., McNall M.C.E., Kaiser G.W., Cooper J.M., McTaggart-Cowan I., Dawe N.K., 1997, Birds of British Columbia, Volume 3 Passerines – Flycatchers through Vireos, UBC Press, Vancouver, p.11. https://books.google.ca/books?id=xynPkpa6vToC&pg=PA11&lpg=PA11&dq=campbell+northwestern+crow+population&source=bl&ots=xGLv4onQpm&sig=D6ERfD2KLeho_HtrFQdw2XQf1vw&hl=en&sa=X&ved=0CCYQ6AEwAmoVChMI7rvCp53yyAIVUKWICh3H8QII#v=onepage&q=campbell%20northwestern%20crow%20population&f=false

B.C. Conservation Data Centre. 2015. Conservation Status Report: Corvus caurinus. B.C. Minist. of Environment. http://a100.gov.bc.ca/pub/eswp/esr.do;jsessionid=5pCQSVnfh3vwyxBLPbzWntmyq8KvDqhnpNV04xrGpywP3nmyprbm!1298844341?id=18443 (Oct. 30, 2015)

B.C. Ministry of Environment, 2015, Human/Wildlife Interactions, Nuisance Fauna, Birds http://www.env.gov.bc.ca/cos/info/wildlife_human_interaction/docs/nuisance_fauna.html#birds (Oct. 31, 2015)

Alaska Department of Fish and Wildlife, 2015, Small Game Hunting in Alaska, Regulations http://www.adfg.alaska.gov/index.cfm?adfg=smallgamehunting.regulations (Oct. 31, 2015)

Van Hemert C., Handel C.M. and O’Hara T.M.,  Evidence of accelerated beak growth associated with avian keratin disorder in black-capped chickadees (Poecile atricapillus), Journal of Wildlife Diseases, vol.48, p.686 http://www.ncbi.nlm.nih.gov/pubmed/22740534

Colleen M.H,  Pajot L.M., Matsuoka S.M., Van Hemert C.,  Terenzi J., Talbot S.L.,  Mulcay D.M., Meteyer C.U. and Trust D.A., 2010, Epizootic of beak deformities among wild birds in Alaska: an emerging disease in North America?,  The Auk, v. 127 pp. 882-898  http://alaska.usgs.gov/science/biology/landbirds/beak_deformity/pdfs/Auk_Handel_beak_deformities2.pdf

Marzluff J.M., McGowan K.J., Donnelly R. and Knight R.L., 2001, Causes and consequences of expanding American Crow populations, Avian Ecology and Conservation in an Urbanizing World,  Kluwer Academic Press, Norwell, MA. p.331 http://www.birds.cornell.edu/crows/Marzluff%20et%20al%202001%20Avian%20Urb%20Ecol.pdf

J. Kay, Environmental Health News, Winged Warnings, Twisted beaks: Scientists exploring mysterious deformities focus on new virus http://www.environmentalhealthnews.org/ehs/news/2014/aug/wingedwarnings6deformed-chickadees  (Nov. 2 2015)