Tag Archives: Avian keratin disorder

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

Crow curiosities: Causes and consequences of bill deformities

If you live in the Pacific Northwest, chances are you’ve come across a crow that’s made you do a double take. No, not for an unusual behavior or vocalization, but for what might be described as an overgrown, monstrous even grotesque looking bill.  Bills like the one belonging to a bird in south Seattle I recently came across during one of my field experiments.  It is, at best, unsettling to see something like this.  So what exactly is going on here?

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A “crossbill” crow living in a south Seattle neighborhood

First, it’s helpful to understand the different layers of a bird’s beak.  The beak is comprised of bone overlaid with a horny structure made of keratin (for you Scrabble people out there it’s called the rhamphotheca).  Keratin is the same stuff that makes up our hair and fingernails and, just like our nails, the rhamphotheca is always growing and wearing away.  For most birds, this growth is very slow which means that keeping bills nicely manicured takes no special effort.  For birds suffering from what’s now termed Avain Keratin Disorder, however, the growth can be as much as 2x as fast as normal, making it impossible to keep things in check.  This growth results in bills that are extra long, decurved on the top, bottom, or both, or overgrown and crisscrossed like my friend in Seattle.  Even if the bill is clipped or broken, it grows right back.

Across most of the country, incidences of AKD in crows are other birds are rare.   Which means that, unless you’re the afflicted individual, there’s no real cause for alarm.  If you live in the PNW, especially Alaska, however, it’s not only increasing common, it’s spreading.

Data taken between 2006-2008, indicates that 17% of Northwestern crows in Alaska have AKD, the highest rate of deformities ever recorded in a wild population1.   Needless to say, the alarm bells, gongs and vuvuzelas are going off within the scientific community.

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So what causes AKD?

~In 10/2016 I published a new post with the most current information on causes.  For now though, I will leave the ’causes’ content in this post as-is, so readers have access to the history of scientific thinking and progress on AKD research.~

Well, lots of things can.  Heat stress, diet, genetic disorders, environmental contaminates, parasites, or bacterial infections have all been linked to the disorder in individual cases.  Given that it affects residential, adult birds, environmental contaminants seem a likely suspect.  But tests on afflicted birds (mostly chickadees) show no consistent correlation with the top suspects like heavy metals and trace elements, organic pesticides, and toxic environmental pollutants like PCBs, PCDDs, and PCDFs.  Future studies will look at compounds like PCDD-Fs, polycyclic aromatic hydrocarbons, and emerging contaminants such as brominated compounds (stuff found in flame retardants which were used for wildfire suppression)2.  For now though, there’s no clear culprit for the disorder’s spread across Alaska and the PNW.

Is it fatal?  That really depends on the nature of the growth.  The main problem is that it can affect eating and preening, both of which are critical to survival, especially in cold climates.   But animals (including people of course) are amazingly adaptable, and according to the USGS, a surprising number of individuals find mates and breed (though reproductive success is lower3).  Indeed, even my friend in Seattle was followed by the “wah! wah!” of its relentlessly begging juvenile.

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The good feather condition and successful fledgling of at least one offspring suggest that this bird is, for now, managing just fine.

Is there anything I can do?  Yes, report your sightings!  Help scientists track the spread and proliferation of this disorder by documenting and reporting whenever you encounter it.  You can do so at the USGS site here.  As far as the individual bird is concerned, you can make feeding easier by supplementing with easy to ingest foods, like this Birdie corn “bread” recipe.  And as always, make your yard safer to vulnerable birds by providing lots of cover and keeping unattended pets indoors.

Make feeding easier by providing meals which can be easily ingested and offer big nutritional value.

Make feeding easier by providing meals which can be easily ingested and offer big nutritional value.

Literature cited:

1.  Van Hemert, C., & Handel, C.M. 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. http://alaska.usgs.gov/science/biology/landbirds/beak_deformity/contaminants.html

3. http://alaska.usgs.gov/science/biology/landbirds/beak_deformity/effects.html#reproduction

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Filed under Crow curiosities, Crow disease