Response of birds to mixed forests structure

Description

We compared bird diversity and abundance between protected natural and managed forests representing temperate mixed forests of Central Europe dominated by beech, spruce, and fir. The bird census was performed in 2021 and 2022 using the point-count method at 173 census points (88 in strictly protected areas; 85 in commercial forests) along with habitat surveys focused on potentially most important habitat variables that influence habitat selection of birds.

Steps to reproduce

The point-count method with a fixed 100-m radius was applied to estimate bird abundances. Three visits were carried out to survey all bird species present in the area, both residents and migrants. Visits were conducted during the breeding season in 2021 and 2022 (April 1–20, May 1–20, May 25–June 15). We allowed at least a two-week break between consecutive visits at the same site. Census points were at least 300 m apart to minimize the probability of double registrations of the same birds and to avoid spatial autocorrelation. All points were located at least 100 m from forest edges to avoid inclusion of species associated with edge ecotones or open habitats (see Batáry et al., 2014). Surveys were conducted early in the morning, from sunrise to approximately 10 A.M. Central European Time in the absence of rain and strong wind. All visually and acoustically observed birds were counted during a five-minute period at each point. The number of individuals for each species at each point was assigned the highest number detected during the three surveys. Species with large home-ranges, such as diurnal and nocturnal raptors (Falconiformes), black stork (Ciconia nigra), and corvids (Corvus sp.), were recorded, but they were not included in the analyses because the survey method used does not adequately estimate their abundances. Nocturnal species were not specially monitored. We attempted to include the potentially most important habitat variables that influence the habitat selection of birds (Table 1). Five variables (type of management, stand age, exposure, altitude, and inclination) were evaluated using maps, geoportal services, and forest management plans. Portion of clearings was assessed (visual estimate) within a radius of 100 m around each census point. The remaining variables, stand and vegetation structures, and dead wood, were estimated or measured within a radius of 25 m around the census points. The volume of SDW and lying dead wood (LDW) at each point was calculated based on the diameter (for standing samples at breast height – DBH; for lying ones at the middle of the log) and height (standing) or length (lying) of dead trees or logs and the assumption of a cylindrical bole shape. Estimates of canopy cover, shrubs, ground vegetation, litter, and tree composition were assessed following Khanaposhtani et al. (2012). Proportion of cavity nesters was computed for each census point using bird abundances and our knowledge of species biology and ecology under similar conditions (Kropil, 1996a, b). Finally, species were classified according to the species conservation priority list of the Bird Directive of European Union (NATURA 2000 species; only Annex I species were considered; Directive 2009/147/EC).

Institutions

• Polska Akademia Nauk Instytut Systematyki i Ewolucji Zwierzat

  Krakow
• Ceska Zemedelska Univerzita v Praze

  Praha, Praha
• Technicka Univerzita vo Zvolene

  Zvolen

Categories

Funders

• Operational Programme Integrated Infrastructure

  Grant ID: ITMS 313011T678
• Operational Programme Integrated Infrastructure

  Grant ID: ITMS 313011V465
• Slovak Research and Development Agency

  Bratislava Region, Slovakia

  Grant ID: APVV-19-0183
• Operational Programme Research and Development within the European Regional Development Fund

  Grant ID: ITMS 26220120006
• Research and Development within the European Regional Development Fund

  Grant ID: ITMS 26220120049

Licence