The Common Buzzard Buteo buteo Population in a Changing Environment, Central Poland as a Case Study

Abstract

Common buzzard is the most abundant bird of prey in Europe, and its population has undergone serious changes. In this study, we focused on a population in Central Poland (study area 105 km2, forests around 24 km2, seven forest complexes) to analyze how certain environmental factors influenced population abundance, breeding parameters, and diet composition. The study was undertaken from 2011 to 2018, and the results were compared with data from two study periods (1982–1992; 2001–2003). Current population density was 3.5 pairs/10 km2 of total area and 14.3 pairs/10 km2 of forested area, it was negatively correlated to the abundance of northern goshawk, and it grew in the last few decades. Mammals were dominant prey (72.6% prey items, 38.6% of biomass), but their share in diet changed following rodent availability. A decrease in the share of voles was recorded, reflecting drop in their abundance and dampening of abundance cycles. Breeding parameters were similar to those in the past, and the number of offspring depended on small rodent availability. Buzzards adapted to changes in the stand structure, i.e., when share of Scots pine decreased, they chose it as their nesting tree less frequently. All this showed that buzzard is a very adaptable species.

Food Niche Overlap of Avian Predators (Falconiformes, Strigiformes) in a Field and Forest Mosaic in Central Poland

“…Overall, the mean number of breeding pairs (as recorded on the basis of complex census of breeding pairs conducted in the whole study area every year [ 6 , 8 , 32 , 33 , 34 , 35 , 36 , 37 ]) of all twelve species of avian predators recorded annually was 133.2 and the density was 126.9 pairs/100 km 2 ( Table 1 ). The most numerous birds of prey were the common buzzards, whose density increased over the last decades [ 6 ]. As for owls, the most numerous were the tawny owls [ 32 , 33 ].…”

“…We studied the food composition and food niche overlap of eight birds of prey and owls in seven to 16 breeding seasons, depending on the species ( Table 2 ). For three species, we used published data: the common buzzard [ 6 ], Northern goshawk [ 8 ], and sparrowhawk [ 34 ]. Published data for the tawny owl [ 38 ] and long-eared owl [ 39 , 40 ] were supplemented with unpublished data from 2015–2018.…”

“…We also noted courtship displays, as well as the presence of single birds, to help to locate new breeding sites. Then, each known breeding site was visited every two weeks in the breeding season, i.e., from April to July to collect prey remains and pellets [ 6 , 34 , 38 , 39 , 40 ]. Such time interval limited disturbance caused by the researchers’ visits to the nest and ensured that the prey collection reflected possible changes in the prey composition over time.…”

“…An example of this was found in an owl community in which the distribution of the dominant Ural owl Strix uralensis affected the spatial distribution of the smaller and competitively weaker tawny owl Strix aluco [ 2 , 4 ]. Competition will rise when food resources are limited and changes in the prey abundance on the short- [ 5 ] or long-term [ 6 ] can strongly influence the degree of food niche overlap.…”

“…In the light of this, the aim of this study was to evidence the food niche overlap within the general assemblage of avian predators (raptors and owls) in the breeding season in a field and forest mosaic of central Poland. For methodological and statistical reasons, eight (out of 12 recorded in the area) species of avian predators (some of them, e.g., the common buzzard, reaching very high density [ 6 ]) were included in this study. Considering the high density of raptors in the study area and the coexistence of the whole assemblage of avian predators (i.e., most of them bred in small woods), we expect that their food niche overlaps remain limited.…”