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?


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.


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.


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:




Filed under Crow curiosities, Crow disease

22 responses to “Crow curiosities: Causes and consequences of bill deformities

  1. So interesting – I have never seen a crow in the Vancouver area with the crossed beak, but one of my regulars, Hank, has a pronounced “over-beak” so I suppose that’s a milder form of this phenomenon. Luckily he seems to manage just fine, and often poses in profile for me, as if showing off his distinguished looking profile. Love your blog posts – I learn interesting crow facts every time.

    • That’s the best compliment I can get, thanks June!

    • I just saw a crow with this deformity in my back yard (couldn’t get a pic becuase it saw me lurking in the window). Did a search to see what was up and of course landed on this page, which I’ve been following for some time.

      I’ve been trying to make friends with my local crows since hearing your episode of Ologies. 🙂

      • PS: I clicked on the “Birdie Corn Bread” recipe in the post but it seems the link no longer works. Have found some recipes that are appropriate for parrots and am wondering if these would work for crows as well? Thanks.

      • I would think so, but you’re welcome to send the recipes just in case. Is the bird still around?

      • He’s not a regular but I’ve seen a few times. I try to out out unshelled peanuta when I see him.

        The “bird bread” I made was peanut butter, bacon grease, corn meal, and lots of seeds/nuts. It looked like suet and was very popular, although I don’t know if the crossbeak fren got any.

      • Pardon horrendous grammar/spelling in previous post. Brain faster than thumbs…

  2. Wow – that was so interesting. I have come across at least two cross beak crows in SW Seattle. Go to my blog and you will find photos of them. If you can’t find them let me know. I’ll dig them up for you. 🙂

  3. Paulina

    Amazing. There’s a crow in my neighborhood (which I can confirm has lived in the area for at least 4 years) with this condition. I call him “Funky Beak”. I found this pic on a Google search and couldn’t believe my eyes. I thought I was looking at a pic of Funky Beak. So far he seems to be getting along fine. (In Coquitlam; suburb of Vancouver, B.C.)

  4. Pingback: Crow curiosities: crows without tails | Corvid Research

  5. Pingback: New research on the cause of AKD outbreak | Corvid Research

  6. carol mott

    we started noticing “eddie” a couple months ago, he’s a cross-billed crow that visits the backyard; after observing eddie for a couple months & assuming his bill was damaged by an accident, i started researching cross-billed birds, eddie suffers from a rare condition, avain keratin disorder, akd. eddie is quite the character, he is fun to watch, often he takes food (suet, bread, berries, corn) and soaks it in birdbaths to soften it before he eats it, he is rather smart that way. eddie fits in well with the resident flock of crows in the neighborhood & holds his own, he’s very vocal, seemingly to announce his visits, he is a unique & magnificent creature and i hope he continues to visit & thrive.
    p.s. it’s no easy task to photograph wild birds with an iphone.

  7. Hollye

    some of the crows in my neighborhood in Salem Oregon have developed crusty sores on their beaks and eyes. Our drinking water is polluted with toxic algea blooms from Detroit Lake. From May until July they said it was too toxic for children under 5 and people with compromised immune systems to drink. They couldnt get the toxic levels below the safe standard so the EPA raised the toxic level allowable to be safe for human consumption. My dogs continue to get sick (throwing up)when I give them tap water. My children, me and several friends also get sick with diarrhea when we drink tap water. So I am forced to buy bottled water for my family and animals. I have used tap water to fill the bird baths with. Any ideas???

  8. Martha Clarke

    We have a crow with what I think may be a similar condition. Instead of a crossed beak, the top beak is malformed, when it was a fledgling it had a pronounced hump, that looked “hairy” for lack of a better description. Then the lump was gone, and the top beak looks very thin, and may even have a hole in it. These crows frequent our yard, 3: mother and 2 youth, we watched them for about 2 years. Virginia, 24073

  9. Charmian Nimmo

    I recently saw a crow with an elongated beak at the Mountain View Cemetery. It also seemed quite dishevelled and was missing a lot of feathers on the backs of it’s wings….could be due to molting also… but seemed able to fly well and was partnered with another crow. Couldn’t tell if it was it’s mate or it’s baby..

  10. Karen Felix

    I’ve been feeding crows here in north Surrey for years. One regular is “Captain Hook”. The top beak is quite long but he seems to manage. He’s also aggressive and makes sure to get his share of the food.

  11. balisonealy

    A crow visits me daily. Lower beak too long by about 1″. He/she is scruffy, not being able to preen but does manage to eat by turning head sideways and scooping food with beak parallel to railing surface. I feed shelled, unsalted peanuts, cheddar cheese, whole grain bread with peanut butter or hummus, leftover pasta. I know he is a wild creature but has become MY wild creature and I feel responsible. He does sit within 3 ft and listens to me talking to him — could I trap and have an avian vet trim his beak? Horrible to see something in difficulty. He cannot dig for grubs, cannot rip food. I am a person who needs to help where I see a need — have been laughed at may times for picking worms up off the sidewalk so they would not be stepped on. A rescuer from an early age.

    • Hi there, and thank you for your empathy. Unfortunately there’s nothing that can be done in the long run. This crow is better off learning how to cope with this disease, rather than be only temporarily aided. I know it’s tough to watch though when it’s a bird you’ve become fond of.

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