Feeding ecology and population dynamics of the goshawk Accipiter gentilis in eastern Westphalia, Germany Nahrungsokologie und Populationsdynamik des Habichts Accipiter gentilis im ostlichen Westfalen
Kruger, O.; Stefener, U.
Vogelwelt 1171: 1-8
Aspects of feeding ecology and population dynamics of the Goshawk were investigated from 1980 to 1994 in an area of 250 kg-2 between Osnabruck and Bielefeld, eastern Northrhine-Westphalia (northwest Germany). In 190 the study area was enlarged to 425 km-2. During 15 years, the population density fluctuated between 3.6 and 7.4 breeding pairs (bp) per 100 km-2, with a median of 5.5 bp/100 km-2. The annual mean rate of reproduction varied between 0.5 and 1.8 fledged juveniles per breeding pair and was thus lower than mean values of other studies. There was a significant negative correlation between breeding density and rate of reproduction, which indicates density-dependent population regulation. Systematic surveys of prey remains revealed a strong preponderance of Woodpigeons Columba palumbus as prey. The ten most important prey species contributed over 80% (of the number of individuals) to the diet. Goshawk predation did not pose a significant threat to any of the prey species' populations. There were differences in diet composition between breeding and non-breeding season. During the breeding period, small birds played a more important role (7.4% compared to 4.3%) and the Domestic Pigeon Columba livia was also taken more frequently because of its higher availability in summer. The presence of other birds of prey and owls in the diet (Buteo buteo, Falco tinnunculus, Asio otus, Strix aluco) illustrates the dominant role of Goshawks as predators in the cultivated landscape. Unexpectedly, there was a negative correlation between rate of reproduction and average prey mass per territory. This might indicate the particular importance of small prey items early in the nesting period and/or the low profitability of large prey items (pheasant, hare) during the nestling period, because there are often lost to other predators. On the other hand, the proportions of both pigeon species in the diet correlated positively with rate of reproduction.