Competitive interactions among raptors in boreal forests

Abstract

We examined inter-specific interactions among goshawks ( Accipiter gentilis), common buzzards (Buteo buteo) and honey buzzards (Pernis apivorus) in western Finland in 1983-1996. Because goshawks are among the largest birds of prey species in boreal forests they may take over the nest of smaller and less-competitive forest-dwelling raptors when searching for suitable places for breeding. Accordingly, more than half of newly established goshawk territories were found on the territories previously occupied by the common buzzard and the honey buzzard. Otherwise, territory sharing between these species was rare. Fledgling production of honey buzzards was not associated with the presence of goshawks, probably owing to the almost 2 months later onset of breeding. This probably decreases competitive interactions between these two species. An intensive interference competition, instead, seemed to be evident between common buzzards and goshawks, because the fledgling production of common buzzards was decreased by 20% as a result of failures during incubation and nestling period in the vicinity (<1 km) of occupied goshawk nests. Similarly, territory occupancy of common buzzards till the next breeding season was significantly reduced in the presence of goshawks. Relatively high proportions of occupied buzzard territories (17%) in the study area were shared by breeding goshawks on the same territory. This suggests that although their diets are dissimilar they inhabit similar habitats and might compete for the available prime nesting habitats within forest landscapes. In addition, goshawks benefit from taking over the complete nests of other raptors, imposing upon the original owners of the nest, because building a large stick nest is probably energetically costly. As a large raptor, the goshawk apparently has a competitive advantage over smaller ones, and may have an ever-increasing impact on smaller birds of prey, if there is a lack of sheltered forests inducing competition for the available nest sites.

Territorial occupancy dynamics in a forest raptor community

“…In contrast, in the case of the buzzard and the goshawk, the study area represents the southernmost part of their distribution range (del Hoyo et al 1994). These two species coexist in many forested areas throughout Europe, and their competitive interactions have been studied by several authors (Kostrzewa 1991;Krüger 2002b;Hakkarainen et al 2004). Being the larger of the two species, the goshawk is the dominant competitor that frequently takes over the nests of the less-competitive buzzard (Hakkarainen et al 2004).…”

“…Raptors are particularly well suited to this type of study because most are territorial, live a long time, and show great fidelity to their breeding areas (Krüger 2002a). One of the least studied aspects, however, is the interaction between different species that coexist in the same area and that could potentially compete for the same territories (Katzner et al 2003;Hakkarainen et al 2004;Martínez et al 2008b). In this paper, we study three raptor species that breed in a protected Mediterranean forest area in southeastern Spain: the booted eagle (Hieraaetus pennatus), the common buzzard (Buteo buteo) and the northern goshawk (Accipiter gentilis).…”

Systematic Raptor Monitoring as conservation tool: 12 year results in the light of landscape changes in Dadia-Lefkimi-Soufli National Park

“…This increase might have contributed to the decline in the Honey buzzard, due to inter-specific competition. While Honey buzzards do not have specific habitat criteria for nesting sites, they do locate their nests away from Northern goshawks to avoid their young being subject to predation (Gamauf et al 2013, Hakkarainen et al 2004. The increase in the closed canopy forest in Dadia NP might have allowed the more agile and competitive Northern goshawk to out-compete the Honey buzzard from optimum forest sites, allowing Northern goshawk numbers to increase to the detriment of Honey buzzard numbers.…”

Impact of Dominant Predators on Territory Occupancy and Reproduction of Subdominant Ones within a Guild of Birds of Prey

“…In general, depressing effects of potential intraguild predation can be expressed especially when the populations of guild members share similar nest sites that are accessible both for dominant and subdominant members of the guild [6,10,21,41]. In the Alps, the eagle owl and tawny owl use similar nest sites that are accessible for both species [6].…”