What drives you? Space and habitat use of Red Kites (Milvus milvus) across different temporal and spatial scales
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Philipps-Universität Marburg
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Land use and climate change are the main causes of changing environmental conditions that lead to the decline of species worldwide. To mitigate the effects of climate change, the use of renewable energies, e.g. through the construction of wind turbines, has been strongly expanded in recent decades. However, wind turbines are regularly criticised because, among other things, they lead to habitat loss, barrier effects and collision risks, especially for highly mobile animals such as birds. Among birds, raptors particularly have an expansive space use. To assess the impact of changing environmental conditions and the additional risks posed by wind turbines, it is important to understand the space and habitat use of raptors. I focused my research on the space and habitat use of Red Kites (Milvus milvus) on different temporal and spatial scales. As the distribution centre of Red Kites is in Germany, we have a special responsibility for the preservation and conservation of this species, which is also a flagship species for bird conservation in Germany.
In my first study (Chapter I), I investigated the influence of the intrinsic drivers sex and reproductive instinct on the space and habitat use of Red Kites and whether their influence changes over the course of three different periods within the breeding season. The Red Kites' space use depends on their sex and reproductive instinct, as the activity ranges of females during the incubation period were significantly smaller than those of males or those in the other periods of the breeding season. Thus, these results confirmed that Red Kites show reproductive role specialisation during the breeding season: females incubate the eggs while males provide them with food. Habitat use did not change during the breeding season. Regardless of the period, forests were used less and arable land more than would have been expected due to their availability, which confirms the Red Kites' attachment to agricultural landscapes.
Secondly (Chapter II), I investigated differences in space use between the sexes throughout the entire breeding season and their underlying intrinsic drivers. Again, the reproductive role specialisation of Red Kites were the main drivers of differences between the sexes in flight distances and mean distances to nests. Both flight distances and mean distances to the nest were lowest for females during the incubation period and highest around the fledging of the juveniles, i.e. when the food requirements of the large fledglings are also highest. The role of the males as providers, on the other hand, became visible in the unimodal curve of the flight distances with a maximum in the early phase of fledgling rearing, when females start to support the search for food. Overall, the males' space use was more constant than that of the females, which was also reflected in the hardly changing mean distance to the nests and indicates that territoriality is present throughout the breeding season, but more pronounced in the male than in the female Red Kites.
Thirdly (Chapter III), I analysed the influence of the extrinsic driver wind speed on the three-dimensional space use of Red Kites and the resulting consequences for their collision risk with wind turbines. Flight activity and flight altitudes of Red Kites changed non-linearly with the occurring wind speeds. While Red Kites were least active at rather calm wind speeds up to 2 m/s at 10 m above ground, their activity increased with increasing wind speed until it reached its maximum at wind speeds of 4.8 m/s-6.8 m/s. Up to wind speeds of 4.4 m/s, the flight altitudes of the Red Kites were constantly just above 100 m above ground and thus at rotor height of both, wind turbines currently operating, and currently planned, taller wind turbines in the study area. At wind speeds between 4.4 m/s - 6.0 m/s, the flight altitudes of the Red Kites decreased by ~ 1 m per 0.1 m/s and ranged around 83 m ± 8 m (mean ± SD). The percentage of flights at rotor height of the operating wind turbines in the study area was between 32 % and 57 %, depending on the individual turbine height. As currently planned wind turbines are taller, the percentage of flights at rotor height of future wind turbines might decrease to 31% - 37%, which is still not a negligible amount. Therefore, mitigation measures to reduce the collision risk of Red Kites will remain indispensable in the future, for which my study provided some promising starting points.
Fourthly (Chapter IV), I investigated the differences in space and habitat use between summer (breeding season) and winter (non-breeding season) habitats of the migratory Red Kites and their underlying intrinsic and extrinsic drivers. Activity ranges and daily flight distances were significantly larger in winter than in summer, probably due to territoriality being a more pronounced driver for space use in summer than in winter. In winter, females showed a more restricted space use than males, while the opposite was true in summer. In summer, however, breeding success played a decisive role: there was no difference between the sexes in successfully breeding Red Kites, while in unsuccessfully breeding Red Kites, females had larger activity ranges than males. This result again indicates a more pronounced territoriality of male than female Red Kites. Regardless of the season, activity ranges and daily flight distances increased with increasing primary productivity (NDVI), which served as proxy for resource availability, which is known to influence birds' space use, for example during migration. However, the activity range sizes and daily flight distances decreased with increasing landscape diversity, most likely due to the coarse resolution of the land use data used in the study. Habitat availability within the activity ranges differed significantly between seasons and can be explained by the different landscape features in winter (south-western Europe) and summer habitats (central Europe). Habitat use also differed between seasons: Agricultural landscapes were used more in winter than in summer. Overall, I was able to show with this study that both intrinsic and extrinsic drivers influence the space use in the two seasons, which results in differences in space and habitat use between their summer and winter habitats. The results underline the importance of considering the entire annual cycle of migratory species for conservation management.
To conclude, during my studies on the space and habitat use of Red Kites at different temporal and spatial scales I identified important intrinsic and extrinsic drivers for their movement. From these, I was able to draw conclusions that might contribute to the evaluation of existing and the development of further efficient conservation measures. Through efficient conservation measures and the role of the Red Kite as a flagship species for bird conservation, we can not only fulfil our special responsibility for the protection and conservation of the Red Kite, but at the same time protect many other species that are threatened by changing environmental conditions.
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Created: 2022Issued: 2023-01-30Updated: 2023-01-30
Faculty
Fachbereich Biologie
Publisher
Philipps-Universität Marburg
Language
ger
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DoctoralThesis
Keywords
Landnutzungecologybird of preyBiologieWindRaumnutzungÖkologiemovementHessenOrnithologieecologyGreifvögelNaturschutzland useArtenschutzRotmilanraptorornithologyconservationBewegungsökologie
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570
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Spatz, Theresa (0000-0003-0713-6093): What drives you? Space and habitat use of Red Kites (Milvus milvus) across different temporal and spatial scales. : Philipps-Universität Marburg 2023-01-30. DOI: https://doi.org/10.17192/z2022.0222.
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This item has been published with the following license: In Copyright