Eurasian Goshawk nesting in relation to prey numbers in Telemark, southern Norway

Sammendrag

Cover photo: Eurasian Goshawk Accipiter gentilis eating a Hooded Crow Corvus cornix. Photo: Kjetil Salomonsen.

In southern Norway, the breeding density of Eurasian Goshawk Accipiter gentilis has typically ranged between 2–4 pairs per 100 km². However, not all territorial pairs attempt to nest each year. In a ca. 2000 km² forest-dominated study area in central parts of Telemark County, the highest number of nesting attempts recorded per year during 1991–2022 was 46, and the highest number of successful nesting attempts was 40. The nesting success of Goshawks increased with age and was 66.7% for juveniles (n = 12), 79.3% for subadults (n = 82) and 89.4% for adult females (n = 736). The annual proportion of young Goshawk females (juveniles and subadults) depended on the annual proportion of recorded replacements of old females and was positively related to mean temperatures in April. The annual proportion of recorded substitutions was positively correlated with population indices of several important prey species, particularly forest grouse, and without a time-lag. In a multiple regression model, the relative change in the recorded number of Goshawk nesting attempts, compared to the previous year, was positively correlated with a population index for thrush spp. and a combined index for Wood Pigeon Columba palumbus and Hooded Crow Corvus cornix, without a time-lag, and with a combined index for Capercaillie Tetrao urogallus and Black Grouse Lyrurus tetrix, with a one-year time-lag. The one-year time-lag with grouse was most evident when only successful nesting attempts were considered. We conclude that the breeding densities of Goshawk in Telemark are rather stable, and we conclude that annual variation in the number of recorded nesting attempts to a large extent reflects the effects of variation in prey density on the body condition of female Goshawks.