Breeding avifauna of the forest interior and forest edge in the Borki Forest

Abstract The composition and structure of breeding bird communities in the Borki Forest in North-Eastern Poland were investigated separately in the forest interior (years 2012–2014) and at the forest edge (years 2016–2018). In both areas, bird censuses were carried out on three plots located in mature oak-hornbeam, ash-alder and mixed coniferous forest stands. Plots were selected to cover similar forest types, encompass stands of similar age and to have similar acreage, both, in the forest interior and at the forest edge. A standard combined mapping technique for estimating the number of breeding birds was applied and a total of 97 bird species were found to have bred at least once within any plot. Regardless of the forest type, both the number of breeding bird species and the population densities were higher on plots situated at the forest edge than in the forest interior. The mean number of breeding species was over 20% higher and the mean total density of breeding pairs was higher by over 30%. Total population densities on the plots located at the forest edge were higher as a result of an increase in population densities of some individual bird species combined with an increase in the number of breeding species, including non-forest and non-typical forest interior species. The number of nesting species in the edge zone was higher than in the forest interior with common species and generalists clearly dominating. Specialist species typical of natural forests as well as rare and endangered species, such as three-toed woodpecker (Picoides tridactylus), white-backed woodpecker (Dendrocopos leucotos), collared flycatcher (Ficedula albicollis) and red-breasted flycatcher (Ficedula parva), for whom the Borki Forest is an important breeding site in Poland were less numerous. Despite the observed differences and a clear edge effect, bird assemblages inhabiting research plots in the forest interior and at the edge were not fundamentally different. We conclude that the edge zone is inhabited by a poorer-quality variant of bird assemblage typical of forest interior, enriched quantitatively by non-forest species associated with open and/or semi-open areas as well as by synanthropic species.