© Marcel Burkhardt
Nehm, K. (2020)
The overwintering movement behaviour of the Red Kite (Milvus milvus) in Switzerland.
Master Thesis, Faculty of Environment and Natural Resources Albert-Ludwigs-University Freiburg
Since 2015, the Red Kite project from the Swiss Ornithological Institute observes the population and behaviour of Red Kites in Switzerland in a study area between Bern and Fribourg. Previous research suggests that adaptions to changes in environmental factors during winter can vary considerably between individuals. Yet, only few studies have experimentally assessed how intrinsic (i.e. sex) or extrinsic drivers (i.e. food availability, elevation) influence the special use. With the aim to find possible changes in behaviour during winter, a feeding experiment was implemented in the winter seasons, from 2017 to 2019. We calculated seasonal home ranges of tagged Red Kites and compared their summer and winter space use respectively. In particular, we assessed the effect of season, sex, elevation and food availability on a) home range expansion b) horizontal or c) elevational shift and d) the shape or home ranges. The analysis of the GPS-data of the tagged Red Kites shows that home ranges of fed birds in low elevations (below 800 m) are smaller in winter than in summer and there is no remarkable change in shape or the location of the used areas. Unfed birds only change their winter home ranges in higher elevations and home ranges shaped more elongated than comparable winter home ranges in lower elevations. In winter, home ranges of fed birds in higher elevations (above 800 m) are usually larger and more elongated than their summer home range. Further, most Red Kites use several areas in winter, potentially due to roosting sites or anthropogenic feeding sites. In conclusion, Red Kites are more likely to change their behaviour during winter if they use home ranges at higher elevations.