Analysis of the Structural Organisation of the Large Raptor Community in Remdovsky Reserve
Authors:   JSC “ECOPROJECT”, Pchelintsev V.G. , Ivanovsky V.V. ,   Vitebsk State University named after P.M. Masherov
Published: October 2023

Questions regarding the abundance of raptor nesting population and the objectivity of the applied censusing methods have constantly caused and still cause active discussions in the scientific literature (Ivanovsky, Bashkirov, 2002, etc.). This is especially relevant during the creation of protected areas, where, undoubtedly, the size of nesting territories of “umbrella” species – large birds of prey – should be taken into account at the start. In addition to the theoretical component, this question has practical implications. For example, it is necessary to know the capacity of lands for each species when carrying out biotechnical measures aimed at increasing rare species abundance. When calculating the practical results of censuses and theoretical constructions when extrapolating data, a control group is necessary to assess the completeness and quality of the gathered data. In this case, a forest-wetland-lake region that is part of Europe’s northwest Lakeland. Such a region must meet the following conditions: large in area; containing at least three long-term raptor breeding territories (for Golden Eagles such an area may reach 280 km2), and have been studied by professional ornithologists over a long timescale. There is such an area in Russia’s Pskov Oblast (Sein et al., 2018). Research occurred 2014–2018 on the Remda Peninsula, located between Lake Chudskoye and Lake Pskov – an area of 1,000 km2. Three quarters of the peninsula is covered by different types of wetlands. Sparsely populated by humans, Remda Wildlife Game Refuge is located centrally there. Large raptor abundance was estimated as follows: Golden Eagle (GE, Aquila chrysaetos) – four, White- Tailed Eagle (WTE, Haliaeetus albicilla) – 36, Osprey (Pandion haliaetus) – 64 pairs. GIS software was used to calculate distances between nests of all possible pairs of birds of prey. Because only elementary raptor populations were studied in Remda Game Reserve, where individual birds can move between any breeding territories of their species in different breeding seasons, all possible rectilinear distances between all nests were measured, not only those between nearest nests. Average distances between nests of all eagle pairs obtained during field surveys were calculated and a number of parameters were calculated for all pairs of compared species. Custom software was used to verify that samples of measured actual distances conformed to a range of mathematical distributions. The verification showed that, without exception, all samples of distances corresponded to binomial distribution. The resulting data on actual mean distances between nests can be used to extrapolate data on the abundance of Osprey, GE, and WTE in areas containing significant lakes and wetlands in northwestern Russia and Belarus rich in lakes peat bogs. The data analyzed in this study is of not only theoretical value, but also as an applied tool for identifying new nesting sites and clarifying real numbers of nesting pairs of Osprey, WTE, and GE in specific areas. This mechanism envisages the use of a “ring” as a buffer zone, the outer diameter of which is the actual average distance plus the mean error, and the inner diameter equals the average actual distance minus the mean error of these distances. In other words, knowing the coordinates of at least one occupied nest of Osprey, GE or WTE, enables identification on the map of possible nest locations belonging to other pairs of these raptors, taking into account their topical preferences. It is shown that the WTE and Osprey engage in trophic and topical competition. From ecological and statistical points of view, competition between Osprey and the WTE may occur with regard to fishing for prey. A comparative study of the trophic niches of these species shows that reducing of food competition between them is achieved by targeting different size groups of prey species. Despite certain “strained” relations between the Osprey and the WTE, increased abundance of WTE will not affect Osprey population status in the Belarusian Lakeland (Ivanovsky, 2020). In the Ponoi Depression on Russia’s Kola Peninsula, where all fish-rich water bodies are controlled by WTE, Osprey are consequently displaced to oligotrophic lakes (Ganusevich, 1991). In the Osprey – WTE pairing, the main factor in competition is not only the proximity of trophic competitors, but also the proximity of highly trophic hunting grounds. This is evidenced by individual instances of the formation of dense Osprey breeding aggregations (up to 5 pairs) near large fish farms and very productive lakes (Ivanovsky, 2012; Babushkin, 2010). In particularly favorable conditions, this distance is reduced to 0.9–0.7 km (Pchelintsev, Sein, 2015). The nesting and foraging biotopes of WTE and Osprey are disjointed, which explains the lack of strict protection of the species in these territories. GE and Osprey do not nest in upland marshes and near lake systems with an areas smaller than 10 km2. Naturally, peat bogs and lakes are only the “nucleus” within the structure of breeding territories for GE and WTE. Breeding territories for GE (150–200 km2) are much larger than those of the WTE due to the difference in the abundance of their main prey inhabiting peat bogs, eutrophic, and mesotrophic lakes (Ivanovsky, 2014). WTE nests are located on forest islands and ridges among bogs and on their margins. The picture of Osprey nests in Remda Game Refuge shows that a number of nests are located along lines equidistant from the waters of Lake Chudskoye and Lake Pskovskoye. This enables birds to hunt depending on wind and wave directions on any specific lake. The pattern Rybinsk Reservoir (Babushkin, Kuznetsov, 2014) is similar. Thus, the resulting data on average actual distances between nests can be used to extrapolate data on Osprey, GE, and WTE abundance in lake regions in northwestern Russia and Belarus. With the coordinates of at least one residential nest of Osprey, Golden Eagle, or White-Tailed Eagle, it is possible to pinpoint other possible nest locations of other pairs of these raptors on maps.