First winter Common Gull with tiny mirror in wing tip

Saw this Common Gull on the garage roof after lunch today. It has a tiny pale mirror spot near the tip of each outermost primary (P10). This is a known variant but said to be rare according to Gulls of Europe, Asia and North America by Olsen & Larsson (2004), a highly recommended book. This is the first individual I have noted with this characteristic, though it is very subtle here – perhaps can be much stronger (such as in this individual).

This bird is one in which the close relationship between the Common Gull and Ring-billed Gull is particularly obvious.

Here, below, is a Ring-billed Gull, photographed in Santa Monica, CA, for comparison. This bird was photographed in April so is showing much more wear in the wing coverts.

 

Note that the Ring-billed Gull has a more parallel bill, stronger chevron-shaped markings on the neck and flanks and a paler silvery grey mantle. In addition,first winter Ring-billed Gull shows diamond shaped dark subterminal markings on P1-4, which are clearly absent in this Common Gull (below) - instead the markings are lance-shaped and restricted.