older the better? Understanding age associated fitness variation in passerines
Mating strategies vary between species, populations, individuals, and even within an individual. For instance, an individual might use different strategies to maximise its fitness when it is old, compared to when it is young. In most bird species, both females and males engage in copulations outside their pair bond (extra-pair copulations). Extra-pair males are commonly older males. However, whether older males get better at outcompeting younger rivals (the observed effect takes place within an individual) or are simply the ones that live longest (the observed effect arises through cross-sectional comparison between individuals) remains to be clarified. In my PhD, I use an experimental breeding design in a captive population of house sparrows, as well as a long-term dataset from a wild population to study the occurrence of extra-pair offspring and its interaction with parental age. I compare the fitness of within- and extra-pair offspring associated with parental age, quantify fitness consequences of male extra-pair behaviour, and compare reproductive traits of young and old males. In summary, my PhD focuses on extra-pair reproduction in birds and explores how age explains individual variation in fitness.