Migration routes and behaviour of skuas Stercorarius

Abstract

Observations of migrating skuas Stercorarius in Sweden 1982—1995  have been analysed with respect to numbers observed, as well as their seasonal and regional occurrence during spring and autumn migration. Numbers of observed skuas have risen during this period. Increased knowledge of identification of younger birds, increased field activity at optimal weather conditions and for Arctic Skua S. parasiticus probably also a larger breeding population in Northern Scandinavia are the supposed reasons for this. Food shortage along the traditional migration routes for Pomarine S. pomarinus and Long-tailed S. longicaudus Skua may have caused them to change their routes in early 1980's. All three species showed a peak in numbers every third year, coinciding with the lemming cycle on the tundra of Arctic Russia.