Next winter this same bird was seen again... The Viking Gull. The rectrices are rather dark for most and this bird (a male?) has heavily barred upper tail coverts (dark bars broader than the pale bars). Sub-terminal patterns on the primaries from P5 onwards, and a bit of dark on the outer web of P4. In the right wing, P8 has a different pattern and is slightly shorter, as if it was growing later in the season (but this reasoning doesn't explain why wear and brown hue are about equal to the adjacent feathers, see P7). Nonetheless, the tongue on P8 seems to be more defined than it is on P7. In the right wing, P10 has a minor mirror.