SFB-TRR 212

Fitness consequences of niche choice and niche construction: nest site selection and architecture, parasite load and survival in Common Buzzards

The place where an animal chooses to reproduce is an important life history decision and a crucial part of its individualised niche, which may have profound fitness consequences. This is especially true for long-lived organisms using the same site repeatedly over many years, such as birds of prey. In addition to the choice of the site for reproduction, birds construct a nest at this site and while a nest is not only a classic example of an extended phenotype, it can also be regarded as a prime example of niche construction, where an individual modifies its environment to enhance its fitness. Nests of birds of prey provide a unique model system to study the adaptive function of nest choice and nest construction as they are important fitness determinants of their constructors, and can last between one year and way more than a century. The nests are often lined with green vegetation and this has been proposed to be a strategy to reduce parasite burden. Nest site choice and the way the nest is constructed lead to key research questions that are central to the entire CRC, such as how niche choice is mediated by intra- and interspecific competition, whether and how niche construction affect fitness parameters such as parasite load and immune function and how variation in these fitness parameters in turn comes about via gene expression and hormonal priming by parents.

This project will start on the basis of an exceptional long-term data set on individual Common Buzzards (Buteo buteo) that already covers three decades. This data set will be combined and extended with experimental manipulation of nest architecture and a chick cross-fostering experiment. Buzzard chick and blood parasite (Leucocytozoon buteonis) gene expression and hormonal profiles will be analysed, because it is now well known that parents sometimes hormonally prime their offspring in anticipation of the early environment they will experience, including anticipated parasitation levels. Therefore, hormonal priming in buzzard chicks in response to variation in parasitation levels will also be analysed. Thereby, I will elucidate first the inheritance pattern of micro- and macrohabitat niche choices. Secondly, whether nest site selection as an example of niche choice and nest architecture as an example of niche construction covary with parasite prevalence and infection intensity. Thirdly, whether host and parasite covary in their gene expression profiles as a function of both parental niche construction and parasite infection intensity. Finally, the ensuing long-term fitness consequences of parental niche choice and niche construction will be revealed by the analyses of individual life histories of wing-tagged buzzard chicks. This project will hence significantly contribute to the key questions of the CRC initiative by combining a unique data set with field experiments and state-of-the-art analytical techniques.