Linking mechanism to function in flocking birds

A group of birds in coordinated flight is – perhaps owing to its success – a commonly observed phenomenon. This ubiquity suggests that bird species which fly together can achieve substantial evolutionary benefit. The proposed benefits of group flight include enhanced predator avoidance, the use of social information or even aerodynamic advantages. However, we still have little understanding of how these benefits will differ across ecological context or taxa. In this thesis, I argue that a good answer to this question can be found by considering how four response mechanisms interact to govern the selective benefits. The importance of birds’ responses to 1) risk, 2) environmental/navigational information, 3) the aerodynamic environment, and 4) the social environment are mapped out conceptually in the Introduction. I then provide five Chapters of question-led empirical research in collective-flight model species homing pigeons (Columba livia), to manipulate and explicitly test all of the above factors. This empirical work included, in each data Chapter, the use of miniaturised, animal attached biologgers, such as GPS, to determine how the birds respond to these manipulations. The observed response mechanisms are discussed in light of evolutionary theory (in particular a behavioural ecological perspective) and thus are linked to the function for which the mechanism involved.