Tag Archives: sick crow

New research on the cause of the AKD outbreak

Since the nineties, Avian Keratin Disorder has been an increasingly common disorder among Alaskan and PNW crows, chickadees (~17% of northwest crows1, ~6% of black-capped chickadees2) and a handful of other species, that causes gross deformities of the beak such as elongation, curvature or crossing.  I’ve written previously about the details of this disease before, but at that time there was little progress in determining the underlying source of the outbreak.  While AKD can be caused by a variety of things, at the scale it’s being observed now scientists questioned if there was a more consistent underlying factor.  Since AKD can cause discomfort or even death (primarily through the inability to feed or preen) understanding what might be the source of this outbreak has clear management and conservation implications.

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An AKD-afflicted American crow in Seattle, WA.

Among the initial suspects were environmental contaminants such as heavy metals, organic pesticides, and toxic environmental pollutants like PCBs, PCDDs, and PCDFs.   Blood work done on afflicted Northwestern crows, however, showed no significant difference in the 30 blood elements tested compared to unaffected adults or juveniles3.  Fortunately, new research may finally be shedding light on what’s going on.

Disease can be an easy thing to rule out if you know what you’re looking for, but new to science pathogens can evade traditional diagnostic techniques.  To account for this, a team of USGS and university scientists conducted a sequencing study comparing pooled RNA of healthy and AKD positive chickadees, crows and nuthatches in attempt to identify a candidate pathogen2.  Their work appears to have paid off, revealing evidence for a new picornavirus (a family of viruses previously known to science) they are calling poecivirus.  Whereas 100% of AKD-affected birds (23 subjects) tested positive only 22% of the 9 control individuals did.

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Alaskan black-capped chickadee with severe AKD. Photo c/o Martin Renner

Given these small sample sizes, it’s too early to throw our hands up in complete relief of having identified the cause of the AKD outbreak, especially since there’s still much to be done in understanding the potential relationship of this new virus to the environment.  Nevertheless, these findings offer some insight and hope that scientists are on the right track.  With more dedicated work we may soon have a much better understanding of this novel pathogen, its link to AKD, and management options moving forward.

Literature cited

1.  Van Hemert C, & Handel CM. 2010.  Beak deformities in Northwestern crows: Evidence of a multispecies epizootic.  The Auk 127: 746-751.  doi: http://dx.doi.org/10.1525/auk.2010.10132

2. Zylberberg M, Van Hemert C, Dumbacher JP, Handel CM, Tihan T, and DeRisi JL. 2016. Novel picornhttps://wordpress.com/post/corvidresearch.wordpress.com/3363avirus associated with Avian Keratin Disorder in Alaskan birds.  mBio 7 doi: 10.7589/2015-10-287

3. Van Hemert C, Handel C. 2016.  Elements in whole blood of Northwestern crows (Corvus caurinus) in Alaska USA: No evidence for an association with beak deformities.   Journal of Wildlife Diseases 52:713-718 doi: http://dx.doi.org/10.7589/2015-10-287

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Filed under Birding, Corvid health, Crow curiosities, Crow disease, Crow life history, Ecosystem, Uncategorized

Crows with broken beaks

It hurts to look at.  The physical pain incurred at the time of the injury, the likely chronic pain on the path to recovery, the dubious chance of survival, it all makes me reach for my mouth in horror when I see this bird.  To me, the idea of living on in spite of such a grotesque injury seems impossible.   Yet here this bird is, surviving, reminding me of what life is capable of.

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So now that I had my moment of sadness and awe, let’s get to what everyone wonders when they see a bird like this: Will a crow’s beak grow back if it’s broken and if not, can it survive?

Cracks or complete fractures like this can result from a number of things, though the list could be longer since these accidents are so rarely observed firsthand.  Perhaps it was traumatic run in with a window, or perhaps the upper or lower bill got trapped against a fulcrum point and an opposing surface.

As far as the prognosis is concerned, I asked birds experts, wildlife rehabilitators and veterinarians and the answer was always an equivocal ‘maybe’.  Maybe it would heal back to something resembling normal and maybe it would remain stunted. Maybe it would survive and maybe it wouldn’t.  To fully understand the reasoning behind this ambiguity you need to understand how a bird’s beak is actually formed.

Like mammals, birds have two jaws bones that form the upper and lower mandibles.  These bones are surrounded by the nerves and blood vessels that support the beak’s functionality and growth. Protecting these layers is the outer lightweight layer of keratin called the rhamphotheca.  Like our fingernails, this layer is always growing and being replaced.

Depending on where the fracture occurs, the rhamphotheca can grow back enough to abolish the injury.  Unfortunately though, there’s not much room to work with before you hit bone, and the bone cannot be regrown.  In these cases the rhampotheca may heal over the exposed bone, but it may not grow back to full size since the template for its shape (the bone) has been stunted.  Even if it does grow back, it may not do so correctly, leading to twisty shapes.

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A crow skull.  You can see that the jaws bones are almost the full length of a crow’s beak.  The black outer layer, the rhampotheca, adds only a little (think mm) extra length so there’s not much that can be removed from the tip of the bill without hitting bone.

So what’s the prognosis?  Well again, that depends.  Even if the bill does not grow back correctly, or at all, some crows can learn to compensate.  Fortunately, being a generalist helps their chances considerably.  Although some foods may now be out of reach, many crows lean how to scoop, poke, and jab their way to a full stomach everyday. The same cannot be said for many species of bird whose beaks are the cornerstone for consuming a specialized diet.

So while it’s fair to be heartbroken at such an injury, it’s not cause for hopelessness. Many crows will learn to compensate, and go on to remind us of the beautiful stubbornness of life.

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Filed under Corvid health, Crow behavior, Crow disease, Uncategorized