Tag Archives: crow health

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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