Nest-platform, nest-tree, nest-site, home-range and landscape characteristics of the Lesser Spotted Eagle (Clanga pomarina) in relation to its breeding performance in East Carpathians

Abstract

Habitat loss and fragmentation along with altered disturbance regimes cause raptor population declines, but processes, rates and interactions are seldom known. Knowledge gaps remain mainly in large forest-dwelling raptors that use habitats on several spatial scales. Our study focusses on breeding habitats and habitat-associated breeding performance of the Lesser Spotted Eagle (“eagle”) across five spatial scales in Laborecká vrchovina Mts (East Carpathians, Slovakia) during 2011–2016. We calculated two relative measures of breeding performance (breeding attempt index, BAI; nest productivity index, NPI) and related them to habitat characteristics sampled on the nest-platform, nest-tree, nest-site, home-range and landscape scale. We found that eagle‘s breeding performance was best explained by predictors on the home-range and landscape scale. BAI and NPI strongly and consistently increased with increasing distance of nest to the nearest felling site and with occurrence of the nest site on lower slope landforms. Former finding supported ample evidence that logging operations pose agrave threat to eagle’s reproduction, while the latter hinted at its strong preference or even specialization for forest edges, for notably old regional ecotones between montane forests and submontane non-forest formations show lower slope topography. On the nest-site scale, nest productivity (NPI) significantly and strongly increased with increasing percentage of Sessile Oak (Quercus petraea) and decreased with cosine of slope aspect in response to more open and accessible canopy structure resulting from oak appearance in beech-dominated forests and to contrasts in solar radiation, shade and similar north–south effects. On the nest-platform and nest-tree scale breeding performance marginally significantly increased with increasing relative nest height above ground and decreased in nests of natural origin (in BAI). It pointed to unrecognized relevance of relative nest height that may link nest-tree with nest-site scale and reflect atrade-off between nest accessibility and nest protective cover, and to greater nest placement diversity with possible greater vulnerability of natural nests. Differences in breeding performance measured by BAI vs NPI indicated that certain selection pressures may vary significantly during the breeding cycle, e.g., early vs late breeding failures and subsequent learning from negative experience. We recommended several management actions by our results, particularly to advance systematic eagle monitoring, to address multiple scales of its habitat use according to their relative importance, to increase the width of protection zones around nests and adopt new or strengthen existing landscape-scale measures and to follow sustainable forestry as apart of integrated landscape management instead of close-to-nature forestry.