Alvaro Jaramillo wrote:

> As well, the first juvenile CAlifornia gulls have arrived here. The
>three birds I saw had completely black bills, not the typical bicolored bill
>of young Californias. I have noticed this in Vancouver as well. It appears
>that the youngest juveniles have dark bills, that quickly become pale on the
>base. Michael Price has commented that he has observed this as well.
>However, it does not appear to be widely known. Does this only happen on
>some individuals, or is it a general rule?

I think California Gull juveniles at first all have black bills, which
fairly quickly become pink at the base. Interestingly, the same is true
for Ring-billed Gulls, which we think of as having bright pink-based bills
when they are young. This interesting condition may indicate that the pink
bill base is secondarily evolved and that those species with black bases
throughout juvenile plumage (e.g., Western and Glaucous-winged) represent
the primitive state. Among the typical gulls, bill color seems to progress
black --> pink with black tip --> yellow with black tip --> yellow with
black ring --> yellow with red and black spots --> yellow with red spot.

Dennis Paulson, Director phone: (206) 756-3798
Slater Museum of Natural History fax: (206) 756-3352
University of Puget Sound e-mail: dpaulson at ups.edu
Tacoma, WA 98416