© Marcel Burkhardt
Mechanisms of population dynamics in Red Kites
Since the 1970s, the Red Kite has populated the entire Central Plateau of Switzerland with remarkable speed and is now beginning to occupy altitudes above 800 metres. One of the Swiss Ornithological Institute’s major research projects aims to find out how the popular species achieves this.
Since the 1970s, the Red Kite has populated the entire Swiss Central Plateau at a rapid pace, and in the new millennium has gone on to settle in altitudes above 800 metres and in the larger alpine valleys. In the species' traditional areas of distribution in Spain, France, and the northeastern provinces of Germany, in contrast, no such population growth can be observed. On the contrary: In many places, the populations have increased only slightly or even declined. Meanwhile, Switzerland is probably home to many more than the 2009 estimate of 1500 breeding pairs, which amounts to c. 10 % of the species' world population. And the upward trend continues! Switzerland appears to be an attractive wintering destination, too: Currently, more than 2500 Red Kites winter in Switzerland!
The project’s main focus is on investigating the factors that affect survival rate, reproduction rate, immigration rate and emigration rate, and thus can help explain the population growth and distribution of the Red Kite in Switzerland. The current spread to higher elevations makes it possible to study environmental gradients and their effect on populations, especially on breeding success as well as dispersal and subsequent settlement of the young. Patrick Scherler's doctoral thesis and other student projects propose to investigate the following aspects:
- Dispersal and settlement of the young along elevational gradients
- Effects of natural and anthropogenic food supply on breeding success and settlement
- Exploratory and migratory behaviour in the course of the life cycle
- Mortality in different stages of the life cycle
- Effects of spatial environmental gradients on population dynamics
In the Cantons of Fribourg and Bern, extensive territory mapping is conducted each year to investigate the effect of landscape characteristics and food supply on breeding density. In the coming years, approximately 300 juveniles and 70 adult birds will be tagged with solar-powered GPS transmitters. This will allow for the birds to be closely tracked during the remainder of their life span. Mortality, settlement in distant locations, and exact range use during juvenile, migratory and breeding stages can be studied. Controlled feeding of selected broods aims to determine the effect of additional food on breeding success and post-fledging behaviour. Nest cameras monitor incubation and record the food delivered to the young.
The high percentage of Swiss breeding pairs in the overall European population means that Switzerland has an important responsibility for this species. Consequently, the Red Kite is one of 50 priority speciesin the Swiss species recovery programme that the Swiss Ornithological Institute in Sempach runs in collaboration with SVS/BirdLife Switzerland and with the support of the Federal Office for the Environment (FOEN). Understanding the mechanisms and factors that influence population trends is pivotal for the conservation of this European species. The findings can be used for the protection of Red Kite populations in other countries, thus contributing to a pan-European effort of species conservation.
In the first year of research in 2015, one of the highest known territory densities was recorded in the study area. However, only about a quarter of the pairs actually produced fledglings; many did not breed at all. 44 juveniles were equipped with GPS loggers; 30 of them survived until the following spring. You can watch an animation of the tracking from the fledging of the birds to their arrival at the wintering sites via this link: https://www.youtube.com/watch?v=yQASAQImjZk.
Guy Pe'er, Helmholtz Centre for Environmental Research – UFZ, Leipzig
Kontakt und Austausch mit weiteren Rotmilan-Projekten:
Thomas Pfeiffer, Weimar, Germany
Rainer Raab, Technisches Büro für Biologie, Deutsch-Wagram, Austria
Eckhard Gottschalk, Universität Göttingen, Germany
Determinants of stopover sites of migrating Swiss red kites (Milvus milvus).
Quantification of anthropogenic food subsidies to an avian facultative scavenger in urban and rural habitats.
The quantity and quality of nestlings: how food supplementation and environmental factors influence reproductive traits of Red Kites.
The effect of food supplementation on range use of breeding red kites (Milvus milvus) in Switzerland.
Effects of environmental factors on stress physiology of wild Red Kite (Milvus milvus) nestlings in Switzerland.
Fast food, slow birds - a trade-off between foraging and nest attendance modulates parental mobbing in a long-lived raptor.
Can supplementary feeding explain the breeding success of the red kite (Milvus milvus) in Switzerland?
Spatio-temporal variation in small carcass use in urban and rural areas: The effect of site characteristics and predictability.