Reproductive success of a reintroduced population of Eagle Owls Bubo bubo in relation to habitat characteristics in the Eifel, Germany.

Eagle Owls Bubo bubo were successfully reintroduced in the Eifel (Germany) in 1974-1999. Here we analyse whether reproductive success was related to habitat characteristics and if the patterns of habitat use and reproduction changed during the population increase. Microclimatic as well as mesoclimatic conditions influenced reproductive success. Owls nesting in basin-shaped enclosed rocky areas and on poriferous volcanic rocks were more successful than those breeding on other rock- and stone types. Additionally, reproductive success declined with elevation; at lower elevations climate was milder and drier, and pairs were breeding earlier in the season. In cold years pairs were breeding later and reproductive success was lower. Reproductive success decreased with the proportion of wooded area around the nest, probably due to a decrease of open hunting area. Although there was no long-term trend in the average reproductive success, a conspicuous decrease in the number of young per successful brood was detected, which was compensated by a decrease in the proportion of total breeding failures. An interpolation of the reproductive potential in the Eifel showed areas of high reproductive value for Eagle Owls, predominantly in low altitude areas. Only a small proportion of these sites were actually occupied.

Dalbeck L. & Heg D., ARDEA 94 (1): 3-21.