Hastings Harbour in recent winters has been visited by several examples of gulls that could not be firmly identified. These gulls have shown pale plumages and various levels of markings and shapes and sizes corresponding to the white-winged forms of Arctic zones, yet have not been either true Glaucous or Iceland Gulls.
Climatic warming in the Nearctic has meant that the barrier between the Old and New World formed by the icing over of the North-West Passage is lessened in its’ effectiveness as a partition between biogeographic realms. The Audubon Society has modelled the projected effect on the distribution of some of the birds of North America. In the case of the Glaucous-winged Gull of the Pacific it is leading to greater dispersal towards the east and to a change in behaviour. Gene flow between the complex of Larus species is not always well understood as access to breeding colonies is sometimes very difficult. The Glaucous-winged Gull is one of a number of forms which breeds with other closely related species such as the Herring Gull and Glaucous Gull. If climate warming continues there will be a further increase in gene flow from the Eastern Atlantic to the Western.
The Audubon Society have produced maps showing the projected changes in range, linked below;-