Simultaneous measurements of three-dimensional trajectories and wingbeat frequencies of birds in the field

This is the author accepted manuscript. The final version is available from the Royal Society via the DOI in this recordData accessibility: We provide data including images recorded by four cameras, camera parameters, videos showing the time variation of the bird 3D positions, and plain text files that include bird id number, positions, times, velocities, accelerations, and wingbeat frequencies at every time step. We also provide the Matlab codes that were used to: (i) detect birds on images; (ii) reconstruct birds' 3D locations using the new stereo-matching algorithm; (iii) track individual's 3D motions; and (iv) calculate wing motion and wingbeat frequency from tracking results. The code and data are available at: https://github.com/linghj/3DTracking.git and https://figshare.com/s/3c572f91b07b06ed30aa.Tracking the movements of birds in three dimensions is integral to a wide range of problems in animal ecology, behaviour and cognition. Multi-camera stereo-imaging has been used to track the three-dimensional (3D) motion of birds in dense flocks, but precise localization of birds remains a challenge due to imaging resolution in the depth direction and optical occlusion. This paper introduces a portable stereo-imaging system with improved accuracy and a simple stereo-matching algorithm that can resolve optical occlusion. This system allows us to decouple body and wing motion, and thus measure not only velocities and accelerations but also wingbeat frequencies along the 3D trajectories of birds. We demonstrate these new methods by analysing six flocking events consisting of 50 to 360 jackdaws (Corvus monedula) and rooks (Corvus frugilegus) as well as 32 jackdaws and 6 rooks flying in isolated pairs or alone. Our method allows us to (i) measure flight speed and wingbeat frequency in different flying modes; (ii) characterize the U-shaped flight performance curve of birds in the wild, showing that wingbeat frequency reaches its minimum at moderate flight speeds; (iii) examine group effects on individual flight performance, showing that birds have a higher wingbeat frequency when flying in a group than when flying alone and when flying in dense regions than when flying in sparse regions; and (iv) provide a potential avenue for automated discrimination of bird species. We argue that the experimental method developed in this paper opens new opportunities for understanding flight kinematics and collective behaviour in natural environments.Human Frontier Science Progra

Behavioural plasticity and the transition to order in jackdaw flocks

This is the final version. Available on open access from Nature Research via the DOI in this recordData availability: Raw images captured by one of the four cameras and the reconstructed 3D movement trajectories of the jackdaws are provided in Supplementary Movies 1 to 3. The group density and group order for 154 groups are provided in Supplementary Data 1. Plain text files, each including bird ID number, position, time, and velocity at every time step are provided in Supplementary Data 2 to 4. All data required to reproduce the results in this study are included in Supplementary Data 1 to 4. The data analysis codes (including the self-propelled particle model) to generate all figures in the paper are also provided. Supplementary Data, Supplementary Movies, and data analysis codes are available at: https://figshare.com/s/472d354cc9e823a8f48fCollective behaviour is typically thought to arise from individuals following fixed interaction rules. The possibility that interaction rules may change under different circumstances has thus only rarely been investigated. Here we show that local interactions in flocks of wild jackdaws (Corvus monedula) vary drastically in different contexts, leading to distinct group-level properties. Jackdaws interact with a fixed number of neighbours (topological interactions) when traveling to roosts, but coordinate with neighbours based on spatial distance (metric interactions) during collective anti-predator mobbing events. Consequently, mobbing flocks exhibit a dramatic transition from disordered aggregations to ordered motion as group density increases, unlike transit flocks where order is independent of density. The relationship between group density and group order during this transition agrees well with a generic self-propelled particle model. Our results demonstrate plasticity in local interaction rules and have implications for both natural and artificial collective systems.Human Frontier Science Progra

Collective turns in jackdaw flocks: kinematics and information transfer

This is the author accepted manuscript. The final version is available from The Royal Society via the DOI in this record.The rapid, cohesive turns of bird flocks are one of the most vivid examples of collective behaviour in nature, and have attracted much research. Three-dimensional imaging techniques now allow us to characterize the kinematics of turning and their group-level consequences in precise detail. We measured the kinematics of flocks of wild jackdaws executing collective turns in two contexts: during transit to roosts and anti-predator mobbing. All flocks reduced their speed during turns, probably because of constraints on individual flight capability. Turn rates increased with the angle of the turn so that the time to complete turns remained constant. We also find that context may alter where turns are initiated in the flocks: for transit flocks in the absence of predators, initiators were located throughout the flocks, but for mobbing flocks with a fixed ground-based predator, they were always located at the front. Moreover, in some transit flocks, initiators were far apart from each other, potentially because of the existence of subgroups and variation in individual interaction ranges. Finally, we find that as the group size increased the information transfer speed initially increased, but rapidly saturated to a constant value. Our results highlight previously unrecognized complexity in turning kinematics and information transfer in social animals.Human Frontier Science Progra