The co-occurrence of Ural Owls Strix uralensis and Northern Goshawks Accipiter gentilis differs between extensive and fragmented forests

Abstract

ABSTRACT Capsule Territories of the nocturnal Ural Owl Strix uralensis and diurnal Northern Goshawk Accipiter gentilis were spatially associated in fragmented forest but not in extensive forest. Aims To test the hypotheses that (i) the patterns of distribution of Ural Owl and Northern Goshawk territories are different in extensive and fragmented forests and (ii) the distribution of their territories do not depend on local forest structure and habitat variables. Methods The territories of Northern Goshawks and Ural Owls were identified in forests in southern Poland. Spatial analysis was used to examine the co-occurrence patterns of the two species, and multivariate analysis to examine the impact of environmental cues on territory selection. Results Most habitat parameters were not significantly related to the presence of territories of either species. For Northern Goshawk there was a positive association with the occurrence of old-growth patches and a negative association with clear-cut areas and proximity to forest edge in fragmented forests; for Ural Owl there was a significant effect of wood type in extensive forest. None of the habitat parameters distinguished the territories of the two species, suggesting similarity in the habitats used. The territories of the two species were spatially associated in fragmented forests, suggesting some positive interspecific relationship. In contrast, the distributions of the two species were not significantly associated in extensive forest. Conclusions To explain the spatial co-occurrence between Northern Goshawks and Ural Owls we suggest: (i) Ural Owls can occupy unused Northern Goshawk nests in managed extensive forest where there is a deficiency of large tree cavities; (ii) restricted availability of habitat in fragmented forests forces both species to nest in close proximity, and/or (iii) Ural Owls use social information from Northern Goshawks about habitat quality when selecting territories in some landscapes.