2nd winter
Kumlien's Iceland Gull (or x Thayer's Gull?)
Larus glaucoides kumlieni (or X L.thayeri?)
Mar. 22nd 2013 Tokyo Imperial Palace, Japan

This pale grayish 2nd witner gull was found in the bathing gull flock that was composed of  several hundreds of Vega Gulls, some Slaty-backed Gulls and two Thayer's Gulls. Its size and structure clearly fit Thayer's-Iceland complex, not hybrids of  larger species. And the pale appearance obviously seems to be out of the range of normal Thayer's Gull, and virtually (or safely?) within the range of Kumlien's Iceland Gull.

Comparison with a (female-type) Thayer's Gull (above) on the same date.
Note the obviously paler primaries with broad pale fringes to the tips.

Comparison with an adult Vega Gull.
The wing looks clearly smaller.

Comparison with a (female-type) Thayer's Gull (right) on the same date.

Note the obviously paler primaries. Its darkish markings are restricted to the range of P10-P5. By contrast, it extends to the P4 in the Thayer's Gull. The so-called "venetian blind" is formed by only outer 4  primaries in the presumed Kumlien's Iceland Gull, while it is 5 in the Thayer's Gull. And  the white mirror on P10 is nearly two times larger than that of the Thayer's Gull, and ranges over both outer and inner web.

In this shot, the right P9 shows a hint of pale mirror in the inner web, unlike the solid dark P9 that is typical of 2nd winter Thayer's Gull.