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

Abstract

The study upon which this article is based examined the interspecific relationships between three different- sized species, both before and during breeding, within a guild of birds of prey in southern Finland between 1997 and 2007. The study sought to examine how the territory occupancy and fledgling production of the smaller (subdominant) species was related to the vicinity of a larger (dominant) species. Inverse relationships were thought to suggest effects of potential intraguild predation. Three key relationships emerged. Firstly, the vicinity of the dominant eagle owl had no significant effect on the occupancy of nesting territories of the subdominant northern goshawk, while the fledgling production of the goshawk increased as the distance from the dominant owl species increased. Secondly, a significant positive relationship was found between the occupancy of the nearest neighbour nesting territories of the eagle owl and the tawny owl. However, the vicinity of the eagle owl had no significant effect on tawny owl reproduction. Thirdly, the occupation of tawny owl territories showed a nearly significant association with the nesting territories of the northern goshawk. However, no significant relationship was found between the vicinity of nearest neighbour nesting territories of the northern goshawk and fledgling production of the tawny owl. The results of this study suggest that depressing reflections of intraguild predation may be expected when the populations of guild members share similar nest sites or if the nest sites of subdominant members of the guild are accessible for dominant members, or in locally unstable populations of less site-tenacious species that show rapid turnover of individuals rather than in strictly site-tenacious long- term territorial species.