Monthly Archives: October 2016

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

How crows cope with storms

Provided the forecast for possibly historic weather conditions, people all over the PNW are preparing themselves for heavy rain, wind, and the falling trees, debris and power outages that may follow as a result.  For many (though sadly not all) people, these preparations may be as simple as a trip to the grocery store and a commitment to stay within the safety of their homes for the weekend.  But what becomes of our wildlife?  How might they weather the predicted 60mph winds and stay warm enough to survive such conditions?

Despite their delicate reputation, birds are well adapted to survive even intense weather.  This is perhaps unremarkable, given that survival is really the name of the game and that stochastic weather conditions are an inevitable part of an animal’s life. To prepare for such weather events, some research suggests that birds and other animals are sensitive to the pressure drops that anticipate severe weather and increase their food intake as a result1. Since foraging may be altered or inhibited during bad weather, this kind of preparation goes a long way to keep birds sated.  For this reason, making sure feeders are kept stocked or offering high nutrition items such as bird friendly corn bread is the best way you can aid your feathered companions in advance of a storm.

Precisely what a bird does during the height of the storm comes down largely to its life history, such as whether it is a cavity nester and rooster, and whether it’s migratory or residential. For cavity nesting and roosting species such as woodpeckers and chickadees, natural and artificial cavities like bird houses can make good retreats.  Birds that do not already make use of cavities such as crows or hummingbirds, however, will find refuge in the dense vegetation of conifer trees or shrubs.  While the exteriors of trees and shrubs may take a beating, their interior microhabitats can be substantially drier, warmer, and more stable, providing a suitable space for birds to wait out the worst of a storm in safety. Migratory birds on the other hand can simply fly around areas of heavy wind.  As a last resort they may even take shelter in some odd places, like a public restroom.

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A marabou stork finds refuge from hurricane Matthew in a bathroom at the St. Augustine Alligator Farm and Zoological Park. Photo c/o Gen Anderson/via AP

Even if the crows are getting blown around a bit, their hold on a perch is at little risk of giving way.  Since crows are passerines (aka perching birds), their feet lock around a perch at rest, meaning that rather than taking energy to hold on, it actually takes effort to let go.  This keeps them well secured even in windy conditions.  Lastly, their feathers keep them  protected from the rain and cold temperatures that may accompany a bad storm.  Although crows will articulate their feathers for certain kinds of behavioral displays, puffing their feathers also traps insulating air and with it, heat.

 

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A crow puffs its feathers on a chilly morning

So if you find yourself worried about what may become of your crow neighbors over the weekend, take comfort that there is little to worry about.  These animals are adapted to sense and prepare for bad weather, find locations that offer safety, and have the physiology to withstand the kind of weather that makes us want to stay in bed.

Literature cited

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