Sunday, 29 October 2017

Beginner's Guide to Pigment Aberration

Posted by Ethan Denton

Think of the chickadees. Black-capped, Mountain, Boreal, Chestnut-backed. On the whole, they are easy to tell apart, right? Not always! Or maybe you would prefer to ruminate upon some of the blackbird family. Rusty, Brewer’s, Eurasian and Common Grackle are perhaps the first ones to spring to mind. Again, identification is usually pretty straight forward. But what happens when a Black-capped Chickadee has a brown head? Have you ever seen a grackle with white wings?

Eurasian Blackbird, Bath, England (Neil Denton)


When this happens, it is invariably due to a pigment deficiency or oddity – in other words, the bird has a problem with it’s color producing cells and its usual plumage is marred by a contrasting mottling in certain areas of its body. The most common case of pigment aberrations in birds is known as leucism. Leucistic birds are failing to produce any pigment whatsoever, causing the feathers to appear completely white. This may be seen in only parts of the body, or across the entire bird.

Red-winged Blackbird with white tail feather (Quinten Wiegersma)

American Robin (Karl Egressy, University of Guelph)
These cases are very common, and can occur in any bird at varying levels. Mallards and Magpies are, however, particularly susceptible.

Leucistic Mallard from Vancouver area (Ethan Denton)

Similar to Leucism, Albinism is defined as when a bird is entirely white, due to a complete absence of the pigment Melanin in the bird. This is paired with notable pink skin which can be seen around the eyes, legs and beak of a bird. This is definitely rarer than Leucism so be careful when observing pigment deficient birds! Leucism can be seen across a bird’s body, causing it to appear as Albinism, but do not be fooled, and watch for that pink skin to determine it.

Black Vulture (www.audubon.org)

That is it for pigment deficiency, but what about aberrant colors streaked across a common bird? That’s not white, that’s brown, or maybe pink! Pink is not, however due to anything unusual in the bird’s genetics, the fault lies in the bird’s diet, or, as in the case of Franklin’s Gulls, as part of a regular breeding plumage cycle which will be shed at the next full molt. What I’m talking about is when a seemingly inconspicuous bird like, for example, the Black-capped Chickadee below, has an odd brown cap, breast, back or tail.

The Brown-capped Black-capped Chickadee (Ethan Denton)

Photographed in Calgary (Ethan Denton)


There was also recently the strange case of the golden magpie – a homeowner in Calgary, Alberta found a magpie which through a strange process had exchanged some of the traditional glossy black for a shiny coat of golden-brown feathers. This phenomenon is caused by a failure to fully oxidize (combine with oxygen) the melanin the feathers. Add that with some leucism, and you have a pretty cool looking bird!

To finish it off, I’m going to include a photo Josiah Van Egmond took earlier this year. I have seen an Orange-crowned Warbler like this, a completely normal warbler, but with intriguing black marks across the face. Due to the exact opposite problem as leucism, these birds are melanistic, meaning they have too much melanin in parts of their plumage.

Melanistic warbler - note the black triangle on the breast (Josiah Van Egmond)

Have you seen any avian oddities around? If so, I’d love to know and see any photos you may have.
For more Perplexing Plumages, see below:

Mallard vs Gadwall

Molt and Eclipse

Lincoln’s vs Song Sparrows

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