Thanks, Terry, for bringing these photos to our attention and
following up with folks at Cornell. If captive-bred birds were
released in the area, as Anne Hobbs suggested, the origin of the El
Dorado County bird is certainly questionable.

I wanted to clarify some points about possible pigment abnormalities
though. Hypermelanism can affect a bird's bill, skin, eyes, etc.
without also affecting its plumage. In this case, however, if the
appearance of the El Dorado bird were attributable to a pigment
abnormality, I think it would more likely have resulted from
carotenism. That is, rather than dark pigments masking the yellow
via hypermelanism, the bill may have appeared dark because the yellow
was not expressed.

Also, to expand on Walt Koenig's comment, magpies with yellow bills
occasionally appear outside of California, including in the Old
World. In such instances, they generally are quickly dismissed as
carotenoid-enhanced Black-billed Magpies or European Magpies,
respectively. I suggested the reverse might be possible in this case
mainly because I expected a Black-billed Magpie to appear somewhat
larger bodied, longer billed, and longer tailed than a Yellow-billed
Magpie. Yet the birds in the photos look structurally identical.

Jeff Davis
Fresno, CA

On Dec 17, 2010, at 8:44 AM, siberiansiren wrote:
> I contacted Cornell Lab of Ornithology regarding my photo of the
> Black-billed Magpie. Below is their response:
>
> I also would wonder why a melanistic Yellow-billed Magpie could
> have a black beak but not show signs of darker elsewhere (i.e. in
> its plumage).
>
> I also wandered across the hall to ask Walt (I believe he's
> actually written papers about Yellow-billed Magpies) his thoughts,
> and he said that if anything he things that I remembers reading or
> hearing people suggest that some Black-billed Magpies could have
> lighter bills, but never the other way around.
>
> Anne Hobbs
> Public Information Specialist
> Cornell Lab of Ornithology
> http://www.birds.cornell.edu
>
>