Category Archives: Crow disease

October 26, 2016 · 7:03 pm

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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September 6, 2016 · 3:06 pm

Why crows sunbathe

With its bill agape, I watch as the crow fans out awkwardly across the cedar shingles. Pressing the camera to my face I snap a couple photos, pleased to finally capture on film a moment I so often encounter in the field.  Unlike the crow, who’s keeping a watchful eye on the sky, I’m completely taken with my admittedly creepy behavior.  Until, of course, I hear the stiff “Excuse me, can I ask what you’re doing?” from the driver’s window as the homeowner’s minivan pulls up behind me.

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Fortunately for me, crow curiosity isn’t hard to come by and quickly the homeowner is as taken with watching this bird as I am.  “So, what is it doing up there?  I see them like this on my roof all the time” he asks after I give him my credentials.  It is a rather odd sight.  It’s nearly 90˚ and the crows is sitting in direct sunlight, mouth open, head cocked and wings outstretched like it’s injured.  Rather than escaping to shade, it’s joined by its fledgling and together they bake their bodies in the hot sun for a few minutes before gathering themselves and carrying on down to the grass to forage.

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Although the specifics can vary slightly, this general kind of posture can be observed across hundreds of bird species, even those you might not expect to have much opportunity for it like owls.  Often it’s used to dry wet feathers or warm up on a crisp winter morning but, given that they do it even when it modestly heat stresses them, it must have some other physiological benefits beside thermoregulation.

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There are a handful of other reasons that birds may sunbathe, but the big picture is that applying intense heat to feathers is critical to maintaining them in good condition.  For example, sunlight exposure has been shown to suppress feather degradation caused by the bacteria Bacillus licheniformis.1  Heat also helps control ectopatasites, possibly by making them more mobile and easier for birds to remove.2  Lastly, sunning may relieve discomfort caused by molting and promote vitamin synthesis.3

So, far from being a signal of distress or heat exhaustion, observing this posture in crows is like watching them ruffle around in a puddle. It’s a routine, and important part of their self care regimen. Plus, everyone knows a few minutes in the sun just plain feels nice.

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Photo c/o Kathy Brown.  Find more of her great photos on Instagram @kat2brown

Literature cited

1. Saranathan, V., and Burtt, E.H. Jr. (2007).  Sunlight on feathers inhibits feather-degrading bacteria.  The Wilson Journal of Ornithology 119: 239-245

2. Blem, C.R., and Blem, L.B. (1993).  Do Swallows sunbathe to control ectoparasites? An experimental test.  The Condor 95: 728-730

3. Potter, E.F., and Hauser, D.C. (1974) Relationship of anting and sunbathing to molting in wild birds.  The Auk 91: 537-563

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February 8, 2016 · 5:32 pm

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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September 24, 2015 · 1:15 am

The facts about crows and West Nile virus

Ah fall, the changing colors, the arrival of mushrooming season, and the gratuitous consumption of hot drinks makes this season a favorite of mine.  But if you live in a temperate zone like the PNW, there’s one drawback to fall; West Nile virus (WNV).  Make no mistake, since its first appearance in the US in 1999, cases of WNV have been documented year round.  Outbreaks, however, typically peak in late summer and early fall which is why you often start to see increasing media attention directed towards the discovery of crow corpses.  Such is the case with a recent die-off in Spokane which inspired a fleet of recent articles.  My favorite was a post from an otherwise predominately car-focused site called The News Wheel which included the following passage:

“In either case, authorities are telling residents that, should they find a dead or dying crow in the street, that they should under no circumstances handle them…In the mean time, it may be a good idea to replace your car’s windshield cleaning fluid with holy water (just in case).”

I suspect some sarcasm was at work there but, in truth, people can get very worked up about WNV.  So here are some FAQs about crows and WNV intended to keep you safe and informed.

What is WNV?
WNV is an arthropod-borne virus which can cause febrile illness, encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord).  It was first documented in the US in 1999, and exists across most of the world (sigh; the costs of globalization)1.

Why are crows associated with WNV?
No, this isn’t unfair prejudice at work, corvids really do have it rough when it comes to this disease.  In all the documented cases of WNV 80% of them have affected corvids, despite its presence in 300 other species of bird2.  The connection between WNV and climate change means that corvids could be in big trouble which you can read about in a previous post here.

What does a bird sick with WNV look like?
Most birds who contract WNV will survive, but for the many crows and other corvids what won’t, symptoms include trouble with balance both at rest and while mobile, and lethargy.  There won’t be any way to tell if a dead crow is infected simply by looking at it2.

Can I get WNV from touching a crow?
According to the CDC, there is no evidence that a person can be infected by direct contact with infected birds, dead or alive3. That being said, always use gloves when handling wildlife.

Can people get WNV?
Yes, though keep in mind that the virus really doesn’t want to be in you.  Humans and other mammals are considered ‘dead-end’ hosts meaning we generally don’t develop a big viral load and the virus cannot be transmitted from you to other humans via mosquitoes1.

How is it spread?
Mosquitoes, mosquitoes, mosquitoes.  They bite the infected bird and then bite you.   And very, very rarely through blood or organ transfusions, and from mother to baby during pregnancy or by breast feeding1.

transmission cycle

How worried should I be?
I’m not a doctor so let’s let the numbers speak for themselves on this one.  Here are the key stats you should know c/o the CDC1:

  • 80% of infected humans will not develop any symptoms.
  • Of the 20% that show symptoms, most will look like the flu.  It will suck, but you’ll recover just fine.
  • Only 1% of infected individuals develop life threatening symptoms.
  • As of September 22, 877 people have tested positive for WNV in 2015.  Of those 43 have died. That’s about half the number that will probably be killed by bee stings and twice as many as will be killed by cows4.
  • For a look at the average annual WNV incidence by state from 1999-2014, check out this map from the CDC.  Suffice it to say, in most states the incidence per every 100,000 people is less than 1.  As a reference point, about 5-20% of the population gets the flu every year and about 36,000 die as a result5.

How can I protect myself?
The CDC recommends an integrated management plan that includes:

  • Mosquito surveillance (are there lots around, how often are you getting bitten, are illnesses being reported etc.).
  • Reduction of breeding sits (i.e eliminate standing water around your home).
  • The use of chemical and biological mosquito control.
  • And finally, education (which by reading this you’re already doing!).

So, does a dead crow in your yard mean it’s time to break out the hazmat suit? Definitely no, but do Fish and Wildlife a favor and report your crow carcasses.  And if any of your neighbors start to panic, calmly and gently give them the facts.  Or just send them this meme I made you:

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Literature cited

  1. http://www.cdc.gov/westnile/faq/genquestions.html
  2. http://www.seattleaudubon.org/sas/LearnAboutBirds/SeasonalFacts/WestNileVirus.aspx
  3. http://www.cdc.gov/westnile/faq/deadbirds.html
  4. http://wnyyradio.com/news/25-shocking-things-more-likely-to-kill-you-than-a-shark/
  5. http://www.cdc.gov/flu/about/qa/disease.htm

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July 20, 2015 · 8:32 pm

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 Avian 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 population.1 Needless to say, the alarm bells, gongs and vuvuzelas are going off within the scientific community.

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So what causes AKD?

~On 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. 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 lower).3 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 hard boiled eggs. 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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April 11, 2015 · 3:49 am

Why climate change may be deadly for crows

In general, crows love the ways that humans transform the environment.  We plow down forests and replace them with suburbia, creating a perfect mix of the occasional nesting tree and plenty of grassy yards perfect for looking for bugs.  On top of that, we litter and waste food, providing lots of additional foraging opportunities outside of our yards.  And even when we replace the forests with urban epicenters, we build towers perfect for nesting, leave out even more garbage, and make the environment less hospitable to predators.  But this climate change thing, well now we’ve gone too far. Even for crows.

Scientists know that climate change is going to be bad for lots of species, with some projections estimating that by 2050, 15-37% of species in the areas sampled will be committed to extinction if current emission trends continue1. Not all creatures will be worse off as the climate warms, however, some will do quite well.  Who are these lucky creatures you ask?  No, not beautiful sword-billed hummingbirds, or rare pygmy marmosets but…mosquitoes.

GO is a proud (albeit perhaps oblivious) participant in the #iamclimatechange campaign.

GO is a proud (albeit perhaps oblivious) participant in the #iamclimatechange campaign.

Warmer, and in some places wetter, climates are projected to not only increase mosquito numbers but, importantly, increase the incidence rate of West Nile virus2.  Crows are particularly susceptible to WNV over other non-corvids, making this especially bad news for them3.  One study showed that some regional crow populations across the US declined 45% since WNV was first introduced in 19994. As warmer temperatures march north, scientists predict we’ll see WNV not only increasing in areas where is exists now, but spreading to northern latitudes where it may have a particularly acute effects2 (I’m talking to you, Canada!).

By extension, this is also bad news for us, since humans can also get sick from being bitten by infected mosquitoes (there is no evidence we can be infected from handling sick or dead crows, however5).  Not to mention all the other diseases mosquitoes carry that kill people and birds.  So whether you care about climate change because you care about crows, humans, or any of the other organisms that are/will be negatively affected, now is the time to do something about it.  Individuals can have profound effects by making changes in their own lives, and by putting social pressure on others to do the same.  There’s plenty of reason to be hopeful if we act!  To learn more about the #iamclimatechange campaign that GO was nice enough to participate in please check out the tumblr or facebook page.

Citations

1. Thomas, C.D., Cameron,A., Green, R.E., Bakkenes, M., Beaumont, L.J., Collingham, Y.C., Erasmus, F.N., Ferreira de Siqueira, M., Grainger, A., Hannah, L., Hufhes, L., Huntley, B., van Jaarsveld, A., Midgley, G.F., Miles, L., Ortega-Huertam, M.A., Townsend Peterson, A., Philips, O.L., and Williams, S.E. (2003) Extinction risk from climate change. Nature 427: 145-148

2. Tam, B. Y., and Tsuji, L.J.S. (2014) West Nile virus in American crows (corvus brachyrhynchos) in Canada: projecting the influences of climate change.  GeoJournal DOI 10.1007/s10708-014-9609-z

3. Yaremych, S. A., Warner, R.E., Mankin, P.C., Brawn J.D., Raim, A., & Novak, R. (2004) West Nile virus and high death rates in American crows.  Emerging Infectious Diseases, 10, 709.

4. LaDeau, S.L., Kilpatrick, A.M., and Marra, P.P. (2007) West Nile virus emergence and the large-scale declines of North American bird populations. Nature Letters. 447

5. http://www.cdc.gov/westnile/faq/deadBirds.html

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August 16, 2014 · 2:47 am

Identifying crow dieases: Avian pox

Recently, I received an email from someone in distress over an obviously sick crow in their yard. They sent some photos and were wondering about the cause of the crusty areas around the bill and eyes. Although I am by no means an expert in avian diseases, there’s one that’s easy to identify and by far the most common I see in the field so I feel it’s appropriate to provide a brief description of it here.

Bird with a likely avian pox infection as identified by the whitish/pink lesions around the exposed skin. Photo c/o D. Wright

Bird with a likely avian pox infection as identified by the whitish/pink lesions around the exposed skin. Photo c/o D. Wright

Avian pox is a common disease affecting birds across many different orders including songbirds, raptors and game birds. It’s caused by the avipoxvirus of which there are at least 3 different strains. There’s multiple modes of transmission but it’s most often spread by mosquitoes which is why it’s observed more commonly in the spring and summer months. It can also be spread via direct transmission or indirectly through inhalation of dander, feather debris or sharing contaminated food or water sources (a good reminder to regularly clean feeders and bird baths).

There are two types of avian pox: wet and dry. Wet pox affects the mouth, throat, trachea and lungs and is most likely to be fatal because it can eventually cause suffocation. Dry pox infections are easy to identify because they result in visible lesions and scarring on the non feathered areas of the bird. In the early stages small yellow, white or pink blisters form which become large raised areas that eventually burst. This results in the formation of crusty scabs that, on crows, will appear brown or black. As long as the the bird’s ability to feed isn’t influenced by the location of the scabbing the lesions will generally heal in 2-4 weeks. The general health of the bird before the infection, and the presence of any secondary infections that result from the open lesions will influence the bird’s likelihood of survival.

The pox covered feet of a crow fatally weakened by this disease.

The pox covered feet of a crow fatally weakened by this disease. c/o Sarah Ramirez

If you notice pox infected birds at your feeder(s) the best way to protect your visitors is to stop feeding them. This may seem cruel or counterproductive since sick birds need access to consist food sources to fight the infection, but providing food bonanzas concentrate birds and increases the risk of transmission to healthy individuals. Depending on your situation you may be able to provide food to the individual without worry of creating contact between multiple birds.

Please leave a message in the comments if you have high quality photos of your infected birds and would be willing to let me use them in this post.  Thank you!

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