Speed consensus and the ‘Goldilocks principle’ in flocking birds (Columba livia)

Abstract

The evolution of group living transformed the history of animal life on earth, yielding substantial selective benefits. Yet, without overcoming fundamental challenges such as how to coordinate movements with conspecifics, animals cannot maintain cohesion, and coordination is thus a prerequisite for the evolution of sociality. Although it has been considered that animal groups must coordinate the timing and direction of movements, coordinating speed is also essential to prevent the group from splitting. We investigated speed consensus in homing pigeon, Columba livia, flocks using high-resolution GPS. Despite observable differences in average solo speed (which was positively correlated with bird mass) compromises of up to 6% from the preferred solo speed were made to reach consensus in flocks. These results match theory which suggests that groups fly at an intermediate of solo speeds, which suggests speed averaging. By virtue of minimizing extreme compromises, speed averaging can maximize selective benefits across the group, suggesting shared consensus for group speed could be ubiquitous across taxa. Nevertheless, despite group-wide advantages, contemporary flight models have suggested unequal energetic costs in favour of individuals with intermediate body mass/preferred speed (hence the 'Goldilocks principle').

Absence of “selfish herd” dynamics in bird flocks under threat

“…Unlike V-formation flocks, which can benefit energetically by flying in a group, flying in a flock has been shown to come at a cost in pigeons. [26][27][28][29] Even the act of flying with a single other pigeon increases work rate by 18%. 27 That the pigeons are willing to pay this cost suggests anti-predator benefits are the primary driver of flocking, especially from familiar release sites, where the benefit from collective navigational information is reduced.…”

“…We set this threshold at 90% of this first recorded mass, whereby if an individual were beneath this mass, it would be taken out of the study for a day and would join if and when the mass returned to above this threshold. We chose this threshold based on our knowledge (from careful monitoring of pigeons' masses throughout the year) that both seasonal fluctuations and flight days often reduce mass by greater amounts than 10% over the space of two weeks 28,29 . This did not occur throughout the duration of the study for any individual, and pigeons were hence not rested, except on a specific rest day for all individuals on 06/10/2018.…”

The Role of Individual Heterogeneity in Collective Animal Behaviour

“…The behavioural differences arising from phenotypic variation among grouping individuals may thereby be partly or even completely overridden by individuals' tendency to conform [20]. A clear example of social conformity is the convergence of the spontaneous speeds of groups of moving animals, such as bird flocks and fish schools [7,21,27]. Such effects that decrease the variability within groups may drive increased differentiation between groups [25,28].…”

Fine-scale changes in speed and altitude suggest protean movements in homing pigeon flights

“…An anemometer (Kestrel 5500 L, Kestrel instruments, USA) was deployed in an open location at the release site on a 5 m pole and set to record wind speed and direction every 10 s. Flights with an average wind speed greater than 2 m s −1 were not used in the analysis in order to control for the influence of wind on the selection of flight speed, which is already well established (e.g. [ 11 , 38 ]). In addition, circling was identified in the GPS tracks and excluded from the analysis [ 39 , 40 ].…”