American coot collective on-water dynamics

TL;DR

This study investigates the on-water collective dynamics of American coot flocks, revealing how flock size and weather influence the balance between disordered and synchronized phases, with implications for energy and thermoregulation.

Contribution

It provides the first detailed analysis of phase durations and their dependence on flock size and weather conditions in American coots.

Findings

Small flocks spend more time in disordered phases in warm, sheltered conditions.

Large flocks show a balanced phase ratio, shifting with weather severity.

Multiple secondary collective behaviors were observed.

Abstract

American coot (Fulica americana) flocks exhibit water surface (two-dimensional) collective dynamics that oscillate between two primary phases: a disordered phase of low density and non-uniform coot body orientations; a synchronized phase characterized by high density, uniform body orientations and speed. For this small-scale study, data was obtained for flocks of 10 to ~250 members for these phases. Approximate durations of phase occurrences were recorded for different flock sizes and for both relatively calm and severe weather conditions. Results indicate that for timed durations of up to ~ 2 hours, small flocks (10 coots) exhibit a comparatively high disordered/synchronized phase ratio (PR) in relatively warm and well-sheltered conditions (substantially >1); large flocks (~100 or more) generally exhibit a PR near 1, while large flocks spend comparatively more time in a disordered phase in relatively calm conditions (PR somewhat >1), and spend more time in a synchronized phase during severe conditions (PR <1). Data suggests a correlation between flock size and PR; and weather conditions and PR, whereby coupling principles driving on-water collective behavior include energy-savings and thermoregulation. Secondary phases occur, including expanding circle and sequential short distance flight, near-single-file lines, convex and concave arcs, among others.