Meeting Abstract
Rules underlying the collective movements of animals have been described for an increasing number of taxa in recent years, including for some fish, insects and birds. Considerable variation in flock density and network structure has been observed in different species. Complicating the interpretation of this diversity of behavior is a lack of controlled, cross-species comparative data. We address this problem by comparing flock dynamics of three species of shorebirds (Family Scolopacidae) that cover a more than 10-fold range in body sizes and 6-fold range of wingspans (Western Sandpiper, 28.5 g, 0.12 m; Short-billed Dowitcher 105 g, 0.51 m; Marbled Godwit 370 g, 0.79 m). We recorded bird flocks in Humboldt county, California in the spring of 2017 using three cameras recording at 29.97 frames per second. Cameras were calibrated for three-dimensional reconstruction of animal flight trajectories and flocks were reconstructed using automated computer vision algorithms. A preliminary analysis of one flock from each species examined flock densities, as measured by distances between each bird and its nearest neighbor. Average nearest-neighbor distances were 0.78 ± 0.77 m (median ± inter-quartile range; N = 31) for Western Sandpipers, 1.20 ± 0.65 for Short-billed Dowitchers (N = 331) and 1.21 ± 0.73 m for Marbled Godwits (N = 381). This preliminary analysis shows surprisingly little variation in flock density across a gradient of body sizes. Further approaches will include examining the effects of flock size on density and comparing flocking behavior of mixed-species flocks. This will help us interpret the rules underlying flock structuring, and to what degree they are set by the animal’s intrinsic sensory and biomechanical constraints, verses extrinsic factors such as flight speeds and maneuverability of neighboring animals.
