Crow curiosities: what causes white feathers?

ZB in flight.  Photo c/o Sarah Ramirez

ZB in flight. Photo c/o Sarah Ramirez

At a recent field site in Bellevue, one of my regular visitors was the most fantastically leucistic crow I had ever seen.  Naturally, I dubbed him or her “ZB” for Zebra Bird.  One or two white feathers is pretty common but this was something far more spectacular.  Something that, to the naive observer, may look like a whole different species of bird.  In response, I thought it might be helpful to talk about how and why crows have white feathers or other kinds of color aberrations.  First off, let’s put some definitions on the table since there are a few terms that often get mixed up, or have different definitions depending on your source.  The following definitions are based on those provided by Guay et al. 2012.

Albinism results from a complete lack of melanin in both the feathers and all the soft body tissues.  This causes red eyes and pink legs, making it very easy to spot.  Albinism is often associated with poor vision and hyper-activity which quickly removes it from the general population and why, when it is spotted, it’s usually only in young or captive birds.

A complete leucistic crow.  What makes it leucistic and not albino?  The colored irises.

Albino crow spotted in Franklin Park, Seattle*

Leucism is a complete lack of melanin in all or part of the plumage, but not necessarily the soft tissues.  It is sometimes referred to as ‘partial albanism’ but if you’re familiar with the definition of albanism (which hopefully you are now!) you know the term ‘partial albinism’ is oxymoronic.  Leusistic birds can have one or multiple white feathers, as is the case with my friend in Bellevue, or be completely white but with regularly colored eyes.  Their feet and bills may or may not appear pink like that of an albino bird’s.

Schizochrosim is a lack of a particular pigment.  So a bird lacking the phaeomelanin (brown) pigment, for example, would appear grey.

Melanism is exceptionally high deposits of melanin that make the animal appear darker overall.

Carotenism is a change in the amount, distribution or composition of caroteniod (red, yellow, orange) pigments.

Dilution is, as the name suggests, a muting of colors across all or part of a bird’s plumage.

How do these color abnormalities arise?  There are a couple of different pathways including genetics, diet and injury/disease.

Genetics

Albinism is genetic, specifically, it’s linked to a recessive autosomal gene.  If you’re reading this and thinking “autosomal recesisve…what?” remember that humans have 23 pairs of chromosomes. Twenty two of them are autosomal and the last pair are sex chromosomes (you’re either XX or XY, sound familiar?).  Recessive means you need two copies of the gene to express the trait.  What this mutation does is cause an absence of the enzyme tyrosinase, which is used by the body to create some of the colored pigments. Because albinism is heritable, it can be bred into an artificial population by a skilled breeder, which is why you may see things like white tigers and lions in the entertainment business.  Despite their dramatic color variation from their peers, they are not distinct species-an idea I occasionally see being perpetuated on social media.  Genetics also plays a role in leucism, though it’s often only part of a more complicated mechanism.

A leucistic dark-eyed junco spotted at my feeder.

A leucistic dark-eyed junco spotted at my feeder.

Diet

Diets low in protein may also contribute to leucism, as the amino acid lysine has been correlated with increased white feathers.  This is supported by the observation that urban birds (who presumably have a diet lower in meat and protein) typically have more color aberrations than their rural or forested peers.  Carotenism, on the other hand, is very strongly influenced by diet, since animals cannot produce this color on their own.  A very familiar example of this is seeing the white young of flamingos who, in this early stage of life, have not yet had enough time to begin producing mass quantities of their pink pigments.

Age/injury

Lastly, age and injury may also contribute to feathers which fail to correctly pigment though this is poorly understood.  Somatic genetic mutation (i.e mutations that occur after conception) are associated with increased age, and indeed, older crows are more often seen with white feathers.  Avian Pox is known to play a role in carotenism though not much is understood about this.

ZB's eye catching leucism in fligh

ZB’s eye catching leucism in flight.  Photo c/o Sarah Ramirez

*Updates* a previous version of this post contained a typo stating that humans have 24 pairs of chromosomes.
A previous version stated incorrectly that a complete leucitic juvenile could be identified by its correctly colored iris.  Since blue pigments occur irrelevant of melanin, this is not the case.

Lit cited

Guay, P.J., Potvin, D.A., and Robinson, R.W. 2012. Abberations in plumage coloration in birds. Australian Field Ornithology 29 23-30.

29 Comments

Filed under Crow curiosities, Crow life history

29 responses to “Crow curiosities: what causes white feathers?

  1. Hi Kaeli – has the observation that urban birds are more often leucistic ever been properly studied? Is there any published literature on the frequency of leucism in urban versus rural corvids?

    Have just found your site and am enjoying reading about your research Reminds me that I have a short blog post about crows that I want to put up at some point soon.

    All the best,

    Jeff

    • Jeff, the short answer to your question is no, there have not been any systematic surveys done of rural vs urban birds across multiple species-which is what I suspect you meant when you asked if it have been properly studied. There are however, a number of papers which looked at leucisim that mention surveying for a particular species in both urban and rural areas and only finding leucistic birds in the urban areas. This is usually mentioned as an aside in the methods, however, since quantifying the difference between then two areas wasn’t the focus of the papers. It’s a good question though and something that could make a worthwhile citizen science study for sure!

      • You read my mind! Yes, it would make a great citizen science project. Would also be a useful system for tracking individual birds between sites to see how, for example, they move between and use urban parks, because the pattern of white feathers is often very distinctive.

      • Susan

        We saw a brown and white crow in north hill. .is this common?

      • Hi Susan, thanks for your question. The brown feathers likely indicate that this is a young bird, as the first year flight feathers are less heavily pigmented and thus often appear brown in contrast to adult birds. As for the white, we also see a fair amount of those especially in the urban core. So while it might be a stretch to say it’s common, it’s fair to say it’s not uncommon if that makes sense 🙂

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  3. Looking For a white crow or White Crow feathers to use for Snow Crow’s new CD http://www.snowcrow.com read our Philosophy to know more about us.
    Can anybody help us out here??? w white crow feathers to make a mandala with or a white crow we could take a picture of the Band with.

  4. Hi Daniel, what a great concept for a band! I love it. I don’t know how helpful my two cents will be, but I’ll offer them to you anyway. As far as the feathers are concerned I won’t weigh in on that other than to provide the gentle reminder that possession of such objects are violations of the Migratory Bird Treaty Act (under which crows are protected) and punishable by law.
    As for locating a whole, living white crow you could take pictures with my best advice would be to start checking in with local wildlife or birding message boards. Those are often the first places sightings of an unusual individual will pop up. You could also try local wildlife rehab facilities which may receive such an individual in need of care, or may know of someone who has a permit to keep one for public outreach.
    Lastly, if you’re not too worried about your audience taking issue with a biologically inaccurate photo, you could look into whether or not the small populations of white ravens continue to make Qualicum Beach in BC their home. There was a group of three living there in 2010 but I haven’t seen much since then. Good luck and hopefully other commenters will have some additional insights!

    • Would also be worth posing the question on one of the Facebook birding sites; there’s lots of keen photographers on those.

    • Thanks so much, for the direction etc. will continue to search around. I have an artist friends (www.briankeeler.com) who I know could do a great painting, check out some of his allegorical paintings. Graphically could always take a picture of a crows feather and replicate via photo shop, filling in the black w white. At the beginning of the album’s (yes expecting to release a limited # on vinyl) so we have time and options for graphic size.
      The graphic on the web site (from our first CD) is appealing as is, but time for the next step. Thanks Dan and Snow Crow

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  7. Michele

    Can anybody help with a problem i have ?
    we rescued a baby crow and he/she was doing well until last week we ended up with lots of feather loss on the head and a weezing coming form the air intake ?
    any help?

  8. I just wanted to say that I didn’t realise there were white crows in the world til last weekend, when I spotted one in Clitheroe, Lancashire, UK at the weekend. It was totally white….and I got a photo but only on my phone so the quality isn’t great. Then a workmate pointed me in the direction of your blog. Very interesting than you.

  9. Mike Taylor

    On tonight’s ephisode of Animal 999 (12/08) they put a crow to sleep because it had “white feather disease” is this something different?

    • I have never heard of such a thing and cannot find any resources about it. The only thing I was able to find that might fit the description was psittacine beak and feather disease, whose symptoms can include white, streaky feathers. But, as the name implies, this is only a problem for psittacine species (i.e parrots). I am stumped to explain what this “disease” is or why they put the animal down because of it. Any Scottish vets out there that can offer an explanation?

  10. Steve

    Hello. Thanks for the info. I found one that was Leusistic last week. Luckily I had my good camera with. I spent an hour just watching, photographing and a short video (I tried one before the one I got and was having problems). If you’d like to see the pictures let me know. I had a long lens and some are pretty good quality but I don’t think I can put them here.

  11. Hi, found this while looking for explanation for a pair of these I saw earlier in the week in our local ‘castle’ museum park (Cliffe Castle, Keighley). Helpful museum lady said they’d been there all summer. Sibs? One of them has almost-magpie-like wing markings. Would you like photos of these as well in addition to the ones mentioned in previous post? Got a couple of not-very-good shots of one of the pair when I went back with my real camera, but hope to get more because they’re stunning.

  12. Have you even seen ravens with white patches?

  13. Selena

    Hi
    We have a crow’s nest next door in a very high gumtree. It has been there for a few years now and the crows are breeding well. I haven’t noticed until recently that some of the crows have white feathers under their tail feathers as well as a few under their wings. I came onto this site because I was sure that crows were all black but your site has answered my question. We also have magpies breeding in our area but haven’t sited their nest. I had been thinking that the crows and magpies may have interbred. Is this at all possible?
    I live in Australia only 7km from the city so very lucky to have abundant wild life to observe.
    Selena

    • Hi Selena, I was very confused at first when you mentioned the crows were actively breeding but then you clarified that you’re in Australia and now I feel like I have my bearings 🙂 As for your question, the short answer is no, not really. Although the idea of ‘species’ can be a little wishy washy, and we know hybridization happens across lots of different groups, your case would be especially remarkable because crows and Australian magpies are not even in the same family, let a lone species. Australian magpies are actually Artimids (butcherbirds), not corvids (which maybe you already knew). Any mating that might happen between then would therefore defy most of what we understand about animals in terms of mate selection. Does that help?

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