… yellow-legged individuals are present throughout the whole of Scandinavia. (…) We still do not have a solution as to why some argentatus have yellow legs and others not, but it may simply be diet-related. The yellow element among Herring Gulls seems to be more common in areas with a predominating fresh or brackish water habitat. In the Baltic Sea, with its brackish water, anything from 10-75 % of the population in the breeding colonies were recorded as having more or less yellowish legs.
Lars Jonsson in Alula 3/1998
A set of photos of adult Herring Gulls / Silbermöwen (Larus argentatus) from the island of Rügen in the German Baltic Sea from June 2016, to illustrate the variety of leg colorations in breeding birds.
