Relationship between migration and latitude among west European birds

In western Europe, the number of bird species present in summer remains fairly constant at 187-229 between latitudes 35 and 65°N, decreases to 156 by 70°N, and then markedly to 26 and 24 on islands at 75 and 80°N. The number present in winter decreases steadily with latitude from 211 at 35°N to four at 80°N, reflecting the greater withdrawal of species from northern latitudes in winter. The proportion of summer visitors in the local avifauna in summer also increases with latitude from 29% of breeding species at 35°N to 83% of breeding species at 80°N. Conversely, the proportion of winter visitors in the local avifauna in winter decreases with latitude, from 36% of wintering species at 35°N to 8% of wintering species (mostly seabirds) at 70°N to none at 80°N. At most latitudes in the range 35-70°N, while some species leave for the winter, a smaller number of other species move in, mostly from further north. About 23% of breeding species leave western Europe totally in autumn to winter elsewhere, most in Africa south of the Sahara but others in southern Asia and elsewhere. Conversely, 3% of wintering species leave western Europe totally in spring to breed elsewhere, some to the north-west in Iceland-Greenland-Canada and others to the north-east in northern Siberia.