  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.
