Saturday, March 19, 2005

ENV: Albinism

A Note to the TexBirds Listserv

Oh boy, Albinos!

Using the search function of the TexBirds archive will result in some hits on extended conversations here about this subject a couple of years ago. Including, as i recall, some finely tuned and detailed linked explanations of the genetics involved -- for those who want to know more.

And while it's true that there are widely varying "definitions" of some of these terms there are actually practical applications that separate them, once the mechanisms are understood. I'd exercise caution in trying to do too much lumping or splitting of terms as that only confuses the matter. Below i give, i hope, a shallow outline that should result in common accuracy in describing pigment-aberrant critters.

Feathers (and scales in snakes for instance) can have multiple concentrations of multiple pigments. When one of these pigments, say black for ease of understanding, is missing, the color appears washed out -- that is, it is left without the darkness created by the black pigment, in addition to say, red and yellow (those are the three common pigments in nature). This is the generally accepted use of leucism -- some pigment missing, but some pigments left. [But note discussions in of "imperfect" and "incomplete" which look at this from a different angle, and unnecessarily complicate it in my mind].

When all pigments are missing (which makes the dead cell outgrowths like feathers, nails, hair, scales, etc., appear white; and the living cell structures, like skin and eyes appear pink to red because of blood), this is albinism. So albinos look, as most people would recognize it, white.

[It can be argued that albinism is an extreme form of leucism, but it's not helpful in establishing what we're looking at. Yet another way of looking at it is that leucism is a form of "incomplete" albinism (and indeed i have used that approach myself), but i've come to the realization that this obscures the meaning of both terms. The key is to recognize that several pigments are involved and that any or all of them could be deficient or overabundant, and take the conversation from there.]

Now, in addition to how much of which pigments are missing (thus defining an example as albino or lutino/leucistic), you have the opposite extreme in which there is an overabundance of pigment. Someone pointed out that this (referring to melanism -- one form of pigment saturation) is the rarest of the pigment abnormalities. This is sorta true. It is the rarest of the three types (albino, lutino, melano) we generally see. It is caused by an excess of black pigment. It is genetically ingrained in some groups -- buteos for example (dark phase swainson's, dark phase ferruginous, dark phase rough-legs, Harlan's, etc.). This is because at some point that color had an adaptive advantage (which is another subject for some other time). Albinism can be genetically enhanced/ingrained in a population as well -- witness Snow Geese and Great White Heron.

The reason that its rarity is "sorta" true is that you could also have an excess of red or yellow pigment, for example. These are extremely rare in wild birds (Bourke's Parakeet is an example), but are well known in the domestic bird trade where certain species have been bred to enhance these colors (Tennessee Red Bobwhites, Bourbon Red Turkeys, Red Golden Pheasant, Tangerine Ring-necked Doves, etc.). Every once in a while someone will post a picture of a truly bizarre red or yellow bird they've found. [I have pictures of a nearly completely red House Finch from here for example].

[And note that you have to know a bird that is yellow because it is leucistic (all pigments except yellow missing) versus one that is hyperxanthic (has an abundance of yellow) -- the trick is generally in noting whether the patterns created by the other pigments are present or absent. The same would go for other pigment colors as well. Harlan's Hawks may represent an interesting wild example in that most individuals have an excess of black pigment but a deficiency of red pigment, thus resulting in an otherwise odd-looking blackish-and-white Red-tail.]

Then, in addition to how much of which pigments are missing or saturated, you have the additional qualifier of whether or not the deficiency/saturation encompasses the entire bird or only a portion. If only a portion, it is generally labelled as a "partial" albino/lutino/melano (but see the Vermilion Flycatcher scenario coming below). If it is complete, it is called a "total" "pure" "true" or "complete" albino/lutino/melano. Any patchy dark and white/pale bird is going to be a "partial" whatever. When this partial pigmentation is selected for in domestic animals it is variously known as "piebald" "pied" "paint" or (with different genetic bases to them) "calico" "appaloosa" "roan" etc.

The red eye thing is misleading. It results from albinism, and will always be present in a "total" albino, by definition. A bird that is solid white, but with a dark eye cannot be a "total" albino as it has pigment in the eye. It is then a partial albino even if it is otherwise all white (and most albinos with dark eyes have some other dark features somewhere). But from there, the common wisdom sometimes defies the actuality. A partial albino CAN have a red eye when the area of the missing pigment includes the eye; or it might NOT have a red eye, even if the area around it is white. A bird can thus have a completely white head with or without a red eye. Or it might have a completely dark head AND a red eye, defying the logic a bit more. In fact a completely "dark", normally plumaged bird with a red eye (that is normally dark) would be a partial albino, even without a speck of white (though i've never seen one myself).

The Red-winged Blackbird in question has white plumage, not washed out, and it has patches of normal color alternating with patches of white. That combination of characters, regardless of whether or not it has a red eye, make it a partial albino. Again, you could argue for it being called a partial leucistic or partial lutino bird, but that just obscures rather than enlightens.

If you didn't follow all that and just want a key, use this for the more common types:

Bird is pure white with a red eye = total/pure/complete/true albino:
Example of a total albino Tawny Frogmouth. Not certain but this Robin.

Bird is pure white with a dark eye = partial albino:
Example of a pure white partial albino European swift of some kind. This White Wagtail with similar indications.

Bird is patchy dark and white, with red OR dark eye = partial albino:
Example of a partial albino Least Sandpiper. Example of a partial albino Steller's Jay, and a Red-tailed Hawk with tiny hints of color, and, finally a very asymmetrically partial albino Northern Cardinal.

Bird is totally washed out, appearing gray, yellow or reddish where normally dark = total leucistic/lutino: A difficult and fascinating Vermilion Flycatcher, it is described online as a partial albino, and that i think could be argued as accurate, but i think i would call it a leucistic bird simply because it seems to be missing all its black pigment while retaining all its red; note too that describing a bird as a partial or total leucistic may depend on where the pigment should be -- in this case for instance although the bird appears "patchy" it looks to me like it's missing ALL of its black pigment and is best described as totally leucistic for melanin; in any case a dynamite looking bird; and for the typically washed out look, here's a small picture but a good look at a "washed out" looking Canada Goose, and a good look at a leucistic Adelie Penguin, and a leucistic European Starling.

Bird is washed out in patches alternating with dark = partial leucistic/lutino:
This is the hardest to find an example of, but here's one, a partially leucistic Yellow-tailed Cockatoo. To see evidence of the "patchy" nature compare to these normally colored birds.

Bird is washed out in patches alternating with white (in birds otherwise dark), and with or without red eye = partial albino is best description but might also be described as partial leucistic/lutino:
Oops, this was pretty hard to find too, anyway an American Goldfinch that's patchy with elements of normal coloration, leucistic coloration and albinistic coloration. In part because white seems to predominate, plus it's the more extreme aberration, if i had to label this bird i believe i'd call it a partial albino, but you can see the photographer called it partially leucistic which is not inaccurate. And then there's this Red-winged Blackbird which is more normally colored than anything else but shows evidence of both leucism and albinism. A Barn Swallow that could be adequately described as either partial albino or partial leucistic.

Bird is much darker than usual, perhaps black (usually an overall effect, but may rarely be patchy) = melano/melanistic:
First a melanistic Grey Heron. And a melanistic Adelie Penguin. A partially melanistic Emperor Penguin.

And by way of example, using domestic birds:
Here is a rather typical "lutino" Budgerigar in which all pigment is gone except yellow, which is probably enhanced as well (hypomelanistic/hypoerythristic/hyperxanthic).

And an Alexandrine Parakeet with dark pigment gone, with a normally colored bird.

And a Splendid Parakeet with pigment gone except yellow and red (hypomelanistic).

And one of the grass parakeets with pigment gone except red (hypomelanistic/hypoxanthic).

Yellow Golden Pheasant with excessive yellow, absent red and the usual dark markings (hyperxanthic/hypoerythristic).

And Tennessee Red Bobwhites with excessive red (hypererythristic), note the presence of the usual dark markings.

Here's the Google search for albino images -- about 47,000 of them for you to try your luck with

And for leucistic images -- about 1150 images (many less but more likely a confusion of labelling terms than anything -- in fact you'll find examples of both in the other search results.

And for melanistic images-- about 600.

Other useful searches are for albinism, albinistic, melano, melanism, lutino, leucism, xanthic, xanthism, erythrism, erythristic

Final ramblings

[you also should realize that albinism and melanism and variations may be genetic, congenital, traumatic or environmental in nature; and may be symmetrical or asymmetrical (a partial albino can have one red eye and one dark eye!) . . .]

[p.s. in the snake breeders lexicon most of these terms are more finely divided as breeders have selected for a mutlitude of combined pigment deficiencies and saturations -- some of this lexicon is at odds with the general biological descriptions, but has the benefit of being highly accurate]

[p.s.s. leucistic and lutino are synonyms -- leucistic is generally used by ornithologists/birders and lutino by hobbyists and breeders. The term "erythristic" is commonly used for critters with either no red pigment or with an excess. It is also commonly misused in connection with xanthic or yellow pigments.]

[and finally it occurs to me to remind not to confuse badly worn pre-molt plumages with leucistic or albinistic features.]

here are some links to pertinent past discussions of mine: Albinism 1 Albinism 2

And just for fun my devil's advocacy on a bird i believe is now accepted as a Great White Heron(?).

tony g

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