Northern Goshawk (accipiter Gentilis) May Improve Black Grouse Breeding Success

Around the nests of many birds of prey the pressure of nest predators is decreased. This attracts other bird species to breed near nests of those birds of prey in order to benefit from protection conferred. This study examines the possible protective effect of the Northern Goshawk (Accipiter gentilis) on two of its main prey species, the Black Grouse (Tetrao tetrix) and the Capercaillie (Tetrao urogallus). If the Goshawk reduces the number of corvids robbing grouse nests, there should be a larger proportion of grouse females with broods near Goshawk nests during late summer. We compared the proportion of grouse females with the broods observed in wildlife-triangle counts, which were performed along a 12-km-long equilateral triangle in relation to distance from a successful Goshawk nest. Where Goshawks had nested inside a triangle, the proportion of Black Grouse females with a brood was 20 % higher than in situations where a Goshawk had nested 2-3 km away from the center of the triangle. On the other hand, the number of adult Black Grouse rose as the distance from the Goshawk nest increased, but this pattern did not hold with chick abundance. No distance effect was found for Capercaillie. This study thus provided indirect evidence based on quantitative data that Goshawks may create a protective effect for one of its main prey.