Opps, in my original post about partial albinism vs. pied mutation, I made a
mistake (I should always look these things up instead of relying on two-year
old memories from ornithology labs).

Ornithologists actual recognize four types of albinism (Pettingill, 1985,
Ornithology in Laboratory and Field, Academic Press, Inc., pp. 166-167) :

Total: A complete inability to make any melanin pigments. There is no
melanin in the eyes, skin, or feathers and these structures appear pink
(eyes and skin) or white (feathers). They may still be able to produce
carotenoid pigments. He cites a Rose-breasted Grosbeak that had pink eyes
and legs, white feathers except bright pink breast and under wing coverts.

Incomplete: When the melanin pigments are completely absent from the
plumage, or iriis, or skin but not all three.

Inperfect: When all of the pigments are reduced ("diluted"), or at least one
of the pigments is absent, in any or all three areas (my example of the
female Evening Grosbeak in the WSU collection)

Partial Albinism: when the pigments are reduced, or one or more is absent,
from the PARTS of any or all three areas (skin, iris or feathers)

So I think the pied mutation would still fit in the partial albinism.
However, I would hesitate to use the term "pied mutation" until we have
eliminated the possiblity of a non-genetic cause of the "pied" condition.

Sorry for the initial confusion.

On Jan 20, 1999, Paul Talbert wrote:

(snip)
> Mutations in a completely different set of genes are responsible for
>"true" albinism - the genes encoding the enzymes for pigment production.
>This class would include what Deb calls complete and incomplete albinism.


Wow! You know a lot more about pigment production than I do. I would
assume it works the same in birds, even though birds and mammals are not
that closely related. We would have to assume that pigment-production
mechanism was inherited from a common ancestor of mammals and reptiles
(leading to birds eventually). This is probably correct for melanin
production since, I think, all three groups use it.


> In mammals, the main pigments are melanin (black) and phaeomelanin (brown
>or yellow). Birds have these pigments and also get caretenoid (yellow,
>orange, red) pigments out of their diets, and can lose these latter
>pigments if their diet does not supply them.

Pettingill (pp. 42-45) writes that birds have melanin but he doesn't mention
phaeomelanin (perhaps this is a mammal only pigment). In addition, as you
mentioned, birds have carotenoids that they get from their diets and modify
into their feathers. Do mammals have that? In addition, 13 orders of
birds, inlcuding Strigiformes (owls), have other pigments, porphyrins, that
create mostly brown, reds and buff. One porphyrin derivitive, turacoverdin,
is a green pigment found only in the touracos (Musophagidae family). Most
greens, however, are produced by combining the yellow carotenoid with a blue
structural color.
In addition, they have
>structural colors (blues and greens) that are caused by diffraction over a
>pigmented backgound.


As you also mentioned, birds also can color their feathers by changing the
structures on the feathers to alter the lightwaves. The blue on bluebirds
is caused by feather structures interference of other light of other wave
lengths and reflecting of blue bending most of the light to blue wave
length; I think that's why their blue seems so brilliant, even on a drab
day! The iridescent colors on the heads of male ducks and the wings and
tail of a magpie are also a result of structural changes in the feathers
over a black (melanin) base. Hummingbirds have the most obvious structural
coloration; some books consider this a separate class of structural color,
called prismatic, because only one color is really refracted but Pettingill
includes it in iridescent.

> Aviculturalists presumably use "pied" because they breed birds and are
>familiar with heritable pied mutations, of which there are many.
>Ornithologists such as Deb may prefer not to prejudge the reason for
>pigment loss, since they may not be able to follow its inheritance in the
>field, or may encounter dietary loss of pigments.


Absolutely. In addition, loss of coloration can occur over injuries.
If the white is replacing a plumage element (black on the wing or a red
brest patch) it is probably due to a genetic cause. However if it just a
splotch of color (a big white spot on the back of a robin for example), it
is less likely that is a mutation and might be an old injury area.

(snip)
>I would be quite surprised if these white patches had a non-genetic cause.


I would also be surprised, but we just don't know. So I think I would
hesitate to name them pied mutation or pattern mutation until we know more .

>Keep reporting those variants,

Absolutely.

And thanks for the education. I now know what "pied" meands and how pigment
is produced than when I got up this morning (and I refreshed my memory on
albinism).

Deb Beutler
Dept. of Zoology
Washington State University
Pullman, Whitman Co., WA

dbeutler at wsunix.wsu.edu