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.

forest vegetation to a large extent determ ines high numbers o f the Brambling and restricts the occurrence o f the Chaffinch. The northern edge o f the Chaffinch’s distribution is limited by adverse climate that hampers formation o f dense vegetation that is necessary for foraging o f this species. Chaffinches during feeding usually slowly move along the thick branches o f trees, often stop to look for prey, regularly walk towards their goal, pick the food from the adjacent twigs and leaves, mainly by stretching towards the prey items. This foraging method is most efficient in dense tree crowns where the distance between the twigs is small and around large branches along which the birds move, a space filled by leaves and thin twigs is formed (Khlebosolov & Zakharov 1997). Unlike the Chaffinch, the Brambling prefers to keep to the sparse crowns of pines and birches. Its foraging rate is higher than in the former species. Bramblings make practically no stops to look for prey, constantly move along and between the branches by hopping, rarely reach for food, and usually peck the food items imm e­ diately after a hop. This foraging technique is efficient in loose crowns where the distance between the twigs is relatively large, and the density o f leaves and small twigs is low. Therefore, boreal forest ecosystems are an optimal habitat for Bramblings (Khlebosolov & Zakharov 1997). Low productivity o f boreal forests hampers the occurrence o f many highly spe­ cialised bird species. For example, in the southern part o f the forest belt in highly productive communities several titm ice species co-exist: the G reat Tit, Blue Tit, Willow Tit, Crested Tit, Coal Tit, and some others. O f them , the Willow Tit breeds furthest north. The reason for this is that the Willow Tit, unlike many other tits, uses non-specialised methods o f searching for prey and foraging (Khlebosolov 1993, Shemyakina & Zatsarinny 2003, Zatsarinny 2004). In southern highly productive habitats it collects the leftovers after more narrowly specialised titm ice species due to using a broad spectrum o f foraging methods and habitats. Lack o f foraging specialisation allows the Willow Tit to live in more northern areas with poor food supply, whereas other tits cannot colonise poor boreal communities because o f their narrow specialisation (Khlebosolov & Khlebosolova 2005). Some forest-dwelling birds occur not only in the forest but also in other habitats. This is mainly true for the species that for­ age on the ground: thrushes, B luethroats, 107