At 11:27 AM 1/23/99 -0800, Herb Curl wrote:

>I received a 2nd degree (blistering) sunburn on my arm
>while mountain climbing, having missed an area with sunscreen.
>Subsequently that area became depigmented and will no longer tan.

Deb Beutler wrote:

> I have a large patch of white skin on my arm
where I burned it. When you freeze-brand a bison, the hair grows over the
brand but the hair is white. Couldn't the same thing happen in birds? <snip>
My sister's dog has a ring of white hair around his black muzzle from the
string his first master used to tied his mouth shut. He has had it since he
was six months old.

Paul Talbert wrote:

>If I actually did see a robin with a white spot on its back, I would be
>less eager to invoke a pied mutation because the back is an unlikely place
>for this kind of white patch.

And Deb Beutler replied:

>I have seen one like that. While I was assisting a bander in southern
Idaho, we banded a robin with a large patch of white feathers on her back.

And Kelly McAllister wrote:

> I saw that it was a pied robin. Its head was mostly white.
It had white primaries on both wings and a few stray white blotches
elsewhere, like on the back.


Thanks for all these interesting observations. I guess I'm convinced that
pigment loss from injuries is more common than I thought, especially from
burns. I still think that you should be able to make an educated guess
about many cases of partial pigment loss by the distribution of depigmented
areas. Symmetrical placement is almost surely a pattern mutation. Deb's
robin is not typical for a spotting (pied) mutation and injury seems as
reasonable a cause as any. Kelly's robin, on the other hand seems like it
could be a spotting mutation even though it had blotches on the back. The
white primaries are appropriately distant from the spinal cord. The "mostly
white" head probably also includes ventral areas, and it is hard to imagine
that a robin could sustain serious injury to most of its head and survive
without an excellent insurance plan.
I checked the Seward park mutant mallards again, and their (ventral) white
breast spots are not symmetrical and do not coincide with the brown patch
on the normal mallards, so I do not think they have a pattern element
mutation. A spotting mutation seems likely. I am actually more interested
in why they are overall more brown than the normal mallards.
The predominantly ventral white patches that are typical of many spotting
mutations result from failure of the pigment cells to migrate completely,
but I think I recall that there are other spotting mutations that simply
cause some of the pigment cells to die off at random. The spots caused by
these mutations would not necessarily be predominantly ventral. As an
aside, many of these spotting mutations have serious effects on other
tissues as well. For example, deafness in white cats and Dalmatians (dogs,
not humans) occurs because pigment cells are necessary for the proper
differentiation of the inner ear.

Carotenoids:
Besides the consumption of massive quantities of orange juice and carrots,
there are other ways to get carotenoids in your skin. When I was younger
and had a more adventurous fashion sense, and punk hair colors did not yet
exist, I tried applying henna to my hair to see what life was like as a
redhead. I learned that henna is more effective at turning scalp orange
than at turning hair red. On someone who began exhibitng male pattern
baldness at the tender age of 14, it made for an interesting effect.


Paul Talbert
tuisto at oz.net