Fig13_NOCR_maxilla by leaningcedarstudio (broken link)

Northwestern Crow with Overgrown Beak (leaningcedarstudio)


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).


NOCR Deformed Beak Flyer Requesting Public Assistance


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).

NWCrow with deformed beak eating

Northwestern Crow with Deformed Beak (Brian Wallace)

(Juneau Empire)

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).


Distribution Map of NOCR with deformed beaks (Handel et al.)


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:

Alaska Department of Fish and Wildlife, 2015, Small Game Hunting in Alaska, (Oct 31 2015)

B.C. Conservation Data Centre. 2015. Conservation Status Report: Corvus caurinus. B.C. Minist. of Environment.;jsessionid=5pCQSVnfh3vwyxBLPbzWntmyq8KvDqhnpNV04xrGpywP3nmyprbm!1298844341?id=18443 (Oct 30 2015)

B.C. Ministry of Environment, 2015, Human/Wildlife Interactions, Nuisance Fauna, Birds (Oct 31 2015)

Brewer et al., Canadian Atlas of Bird Banding,  2006, Volume 1: Doves, Cuckoos, and Hummingbirds through Passerines 2nd edition, 1921–1995

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.

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

Cornell University, 2015, All About Birds-Bird Guide Northwestern Crow, Life History, (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.

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

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

Kay J., Environmental Health News, Winged Warnings, Twisted beaks: Scientists exploring mysterious deformities focus on new virus (Nov 02 2015)

Link R., 2005, Washington Department of Fish and Wildlife, Living With Wildlife, Crows, (Oct 31 2015)

Marzluff J.M., Angell T.,2008, In the Company of Crows and Ravens, Yale University Press, p. unavailable

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

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 (Oct 27 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

Vancouver Avian Research Centre, Species: Northwestern Crow Corvus caurinus

Ward M., 2013, Crows Over Commercial Drive, Vancouver (video) (Oct 27 2015)


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  1. Kim says:

    Really interesting about the beak deformities. Did they say in the article if the deformities were similar among the crows (ie did they mostly have the hook)? Awesome blog!

    • dana says:

      Hi Kim – Thank-you for your comments! Sadly for the crows the deformities can take many shapes. Hansen and Van Hemert “…documented 3 distinct classes of deformities, elongation of the upper beak, elongation of the lower beak and elongation of both upper and lower beaks…” and,”…they all represent some form of overgrowth and apparently reflect different presentations of avian keratin disorder”. When the disorder affects both the upper and lower portions of the crow’s beak the result looks similar to a Red Crossbill’s beak, but more exaggerated. I saw an image of a chickadee with very elongated beak portions (as long as it’s head) and the upper beak had grown down and then curled back up….

  2. Gillian says:

    Thanks for sharing this very informative blog! I’m definitely going to be keeping my eyes open for beak deformities which is not something I otherwise would have been watching for. Do you have suggestions as to what I should do if I find a crow with a deformed beak? Would you like to be alerted?

    • dana says:

      Gillian that’s an excellent question! If you see a crow (or any bird, for that matter) with a beak deformity, the Alaska Science Centre would like to know about it and they have a simple report form on their website here: They are continuing to actively study this issue. Be sure to document the location you saw the bird very specifically, the species, whether it was banded and take a photo if possible. Of course I’m hoping you don’t come across any, but I’d be interested to know if you do.

  3. 568280788 says:

    I had no idea crows had this problem. Do other members of the flock help care for affected birds that have trouble foraging or grooming?

    • dana says:

      Good question 568280788. I understand NOCR partake in allopreening, that is when nesting partners preen each other, but I’m not aware of any special care the flock takes in feeding or grooming those with beak deformities. The effects of beak deformities on the birds have been thoroughly documented (difficulty foraging and grooming, higher mortality rates, erratic behaviour, and more………) and I see no mention of other birds helping the ones with deformities. I don’t know if the people studying this problem have not looked at the areas you are asking about, or whether they just don’t happen.

  4. Mike says:

    Very interesting post Dana! That this phenomenon seems to be prevalent in just these two species is intriguing, and so geographically diffuse too? Do you have any suspicions about the etiology of this disease?

    • dana says:

      Thanks Mike! Just to be clear, I should point out that there are other species in which similar deformities have been noticed. I mentioned that there were 8 others found near one of the chickadee test sites, but according to the Alaska Science Center, ‘a total 30 species, including 17 residents and 13 migrants, have been reported with beak deformities in Alaska. They range from seabirds and raptors to woodpeckers and passerines…. it’s just that the crows have such an incredibly high occurrence of the disfigurement that they have been a focus for study. Since you were blogging about Red-breasted Nuthatches you may be interested to know that they had the 3rd highest reports of deformities. Anyways, on to your question… Of the all the possible causes that have been tested for (disease, parasites, contaminants, genetic abnormalities) only environmental contaminants and nutritional deficiencies come up inconclusive, every other one shows no clear evidence (so far). There was a previous link between nutritional deficiencies and beak deformities caused by low level contaminant exposure in a colony of Great Lakes cormorants. I suspect we need to be a lot more careful with what we put into our environment…

  5. shar says:

    This is awesome Dana!
    Do you know the average lifespan of a Northwestern Crow? Also, what band size do they take do you know?

    • dana says:

      Thanks Sharlene! I did a little research for you and found that Northwestern Crows are expected to live about 12 years in the wild – and over 16 years in exceptional circumstances. I also found a nice story about Tata the American crow rescued from a cemetery when he fell out of his nest as a juvenile. Tata lived a charmed 59 years in captivity! Here’s his story: As for the band size for NOCR – I still rely on the experts such as you, for that sort of detail, but you just let me know when you have a fine crow that needs a band and I’ll see if a size 4 fits.

      • shar says:

        Aww, he’s so cute! It’s crazy the lifespan change once “pampered”…
        Haha, maybe Eric will share that tidbit of information when he marks these…you know, since he’s actually banded one!

        • Eric says:

          Finally, you can hear from me. NOCR should be gauged, but they should take 4 or 4A. The first one we banded at Buttertubs was a nesting female (wasn’t too happy). She had big tarsi and she gauged at 5. We only had lock-on bands, so she got a 5LO band. Elsie located her again about 6 months later (only banded crow in town!). I banded a juvenile last year that Blair caught at home. That one got a size 4.

          Awesome blog Dana!

          • dana says:

            Ah ha…. Okay, should I ever be so lucky to band a NOCR I’ll be sure to gauge it first. In the meantime, I’ll keep an eye out for the rare banded Nanaimo crows.
            Thanks Eric, it is nice to hear from you!

  6. Robin says:

    The frequency of deformities amongst NW crows is alarming and also intriguing. I wonder if the crows experience a higher incidence of deformity, or whether the higher frequency of deformity present in adult birds indicates the crows are able to survive the abnormalities due to their intelligence, adaptive behavour, and also perhaps their crow-operative social structure?

  7. dana says:

    Thank-you for your insightful comments Robin! While indeed crows are very intelligent and crow-operative (thanks for this awesome new term!!!) it is not necessarily these reasons that has led to the high incidence of crows with beak deformities compared to other species, as none of the species captured showed evidence of beak deformities as juveniles.……If Hemert and Handel can get a handle (uh huh) on the causes of this issue then perhaps they (or someone) will then delve a little deeper into the challenges and successes various species have with beak deformities. Only then we will know if the crows are able to live longer with the deformities than other species due to crow-operation and all that stuff worthy of crowing about….

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