The birds of Pasvik / E. I. Khlebosolov, O. A. Makarova, O. A. Khlebosolova [et al. ; English transl. Nikita Chernetsov]. - Ryazan : Golosgubernii, 2007. - 175 с. : ил., портр.

Generally, the avifauna o f boreal forests is sim ilar to th a t o f more sou thern areas and includes members o f the m ain taxonom ic and ecological groups. However, boreal forests have a num ber o f peculiar features th a t influence the fo r­ m ation o f the specific structure o f the passerine population. The forest ecosystems o f Pasvik are much less complex th a n in more southern areas. Only the tree layer is well developed. Shrub and herb layers are practically absent, forest vegetation is sparse, and the productivity o f forest comm un ities is low. All this results in the lack o f some groups o f birds, whereas others are represented by a small num ber o f species or do not reach high numbers. Diversity o f warblers (Sylviidae) in Pasvik is low. Only one Phylloscopus species, the Willow Warbler, is comm on there. The structure o f boreal forest vege­ tatio n provides optimal cond ition s for this species. Two o th e r species, the Chiffchaff and the Arctic Warbler, are very rare and o ccu r only in some habitats. In more southern areas a high diversity o f Phylloscopus warblers is suppo rted by sever­ al layers o f trees, high density o f tree crowns and shrub, and general heterogeneity o f forest habitats (Khlebosolov et al. 2003). Sylvia and Locustella warblers are p ra c ­ tically lacking in the study area. The reason for this is poo r developm ent o f scrub and herbs that are the main habitats o f these birds. Small areas o f scrub occu r only along the banks o f rivers, lake and swamp coasts. However, this scrub, usually grow ­ ing in wet areas, is better suited for the Sedge Warbler which is th e sole rep resen ta­ tive o f Acrocephalus warblers in Pasvik. Only one thrush species, the Redwing, dom inates in the forest ecosystems o f Pasvik. O ther thrushes only occur in some habitats and play no significant role in the functioning o f ecosystems. The reason for this is a un iform ground layer whose structure is quite im portant for ecological segregation o f m ainly ground-foraging thrushes (Baranovsky et al. in press). In most types o f forest th e ground layer is formed by mosses and lichens that are optim al for Redwings. Areas suitable for other thrushes are restricted and occur locally. The degree o f sparseness o f forest vegetation has a significant im pact on the formation o f specific structure o f birds. This is quite app a ren t w hen relationships o f the two closely related species, the Chaffinch and the Brambling, are analysed. The Chaffinch breeds in most of Europe. The Brambling occurs in Siberia and no rthern Europe where the ranges o f b o th species overlap broadly. In the overlap zone the relative abundance o f the two species regularly varies along th e so u th -n o rth axis. The numbers o f the Brambling increase, whereas those o f th e Chaffinch decrease (Merikallio 1951, H aartm an 1973, Jarvinen & Vaisanen 1979). In Pasvik the Brambling is an abundant species, whereas the Chaffinch is very rare. A com para­ tive analysis o f behaviour and ecology o f bo th species has show n th a t sparseness o f 106