Dynamics of Flocking in Birds

The coordinated movement of large numbers of animals in groups is among the most widespread behaviours in nature, driven by decisions made by individuals. A preference for grouping at the individual level is believed to be driven by an array of benefits that grouping imparts, such as improved anti-predator defence, navigational efficiency, and foraging success. There are often costs to grouping, however, and its advantages may be overridden by pressures imparted by environmental factors or internal conditions. Nowhere is this more apparent than in the large flocks of many bird species, given the high cost of powered flight, and the rapidly changing conditions experienced during flight. Individual birds must decide whether to form flocks, and if so, how to behave and fly within them. These decisions can lead to behavioural changes at the group level. How differences in individual behaviour mediate group movement and formation remains relatively understudied, and this thesis comprised four investigations into aspects of the relationship between individuals, groups, and environments at different scales: (1) How the cost of flight correlates with behavioural changes, e.g. flight effort, flock spread, and group leadership. (2) How birds alter their flight in response to heterogeneous environments. (3) How flight, leadership, and grouping behaviour is influenced by hunger motivation. (4) How three key behavioural traits differ across domestic, feral, and wild populations of the same species. These investigations utilised data collected from experimental flights conducted by flocks of homing pigeons (Columba livia d.) carrying GPS and accelerometery biologgers, and of behavioural assays conducted on domestic and feral pigeons and on members of the UK’s only pure population of ancestral rock doves (Columba livia). My observations are discussed in the contexts of behavioural and movement ecology, and ethology, aiming to expand our understanding of bird flocks, flight dynamics, and the impacts of human presence on animal behaviour.