Tag Archives: crow diease

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 remove2.  Lastly, sunning may relieve discomfort caused by molting and promote vitamin synthesis3.

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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Filed under Crow behavior, Crow curiosities, Crow disease

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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Filed under Crow behavior, crow conflicts, Crow disease, Crows and humans

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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Filed under Crow disease, Crow life history, Crows and humans

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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Filed under Crow disease, Crow life history