Several different aspects of the geographical ecology of tundra birds were investigated during theSwedish-Russian Tundra Ecology -94 expedition along the Northeast Passage in 1994. Quantitative censuses of breeding bird communities and populations were made at the temporary field sites, supplemented by surveys from helicopter over wider tundra areas. The occurrence of avian predatory species-skuas, snowy owl and rough-legged buzzard-was analyzed with respect to interspecific relationships as well as to the abundance of their main prey, the lemmings. Geographical variation in color phases among skuas and of genetics in dunlins (based on mitochondrial DNA) were examined, as well as the social organization in different wader species and moult strategies among populations ofdunlins;Bird migration was recorded by a tracking radar placed on the expedition ship, and by complementary visual observations. These studies demonstrated the patterns of flight directions, altitudes, speeds (also measured by optical instruments) and migratory routes of the tundra birds. Ringing results contributed to put these results into a global migratory perspective. Two important aspects of the energetics of arctic birds were investigated during the expedition: the basal metabolic rates of waders when departing on migration, and the fuel loads deposited by the migrating waders.The effect of longitudinal displacement on the migratory orientation of a long-distance passerine migrant, the wheatear, was tested by repeated orientation experiments at a number of test sites alongthe Northeast Passage.