Abstract <p>Ecological patterns of the formation of bird population in the Onekotan Island were analyzed. A route accounting method on the transects of unlimited width was used. Fifty-three bird species were registered. 38% of the species are ubiquitous; 30%, local; 32%, sporadic. Thirty-eight species nest. A taxonomic structure of the avifauna, formed by the species of 10 orders, corresponds to zonal and landscape peculiarities of island territories located near the eastern edges of northern Eurasia. Passeriformes (38%), Charadriiformes (24%), and Procellariiformes (9%) prevail. A zoogeographical originality of the avifauna is caused by a combination of the elements of Pacific, Siberian, Far Eastern island, Arctic faunistic complexes, Siberian American and widespread species. The avifauna of the Onekotan Island, which is formed in the system of general zonal–landscape and altitudinal–belt patterns, unites the ecological groups of marine and terrestrial (including mountain (<i>n</i> = 7)) species. The species richness, bird population density, and abundance of most species decrease with altitude. The avifauna of the forest belt includes 26 species; subalpine belt, 17 species; alpine belt, 14 species; oceanic waters and coast, 29 species with the population densities of 559, 306, 221, and 129–223 individuals/km², respectively. The similarity coefficient of the avifauna of oceanic regions is 47%; terrestrial habitats, about 60%. The buff-bellied pipit, brown-headed thrush, Siberian rubythroat, Middendorff’s grasshopper warbler, Arctic warbler, and pine grosbeak are among dominants and subdominants in the population of terrestrial habitats. Seven species numerically dominate in the population of oceanic waters: in its coastal part, harlequin duck, red-faced cormorant, slaty-backed gull, and pigeon guillemot; at a considerable distance from the shore, northern fulmar, common guillemot, and tufted puffin.</p>