Competition, predation risk and patterns of flock expansion in barnacle geese ( Branta leucopsis )

摘要: Changes in the spatial pattern of flocks barnacle geese Branta leucopsis were examined relation to individual behaviour during feeding visits farm pastures. The photographed every 10–20 min, and shape location flock was determined from a plan view obtained digitized images photographs. Flocks initially maintained tight formation shortly after arrival, but then tended expand with increasing residence time. rate expansion, however, significantly greater large flocks, small showing no consistent pattern. Observed rates change area compared those simple model movement which individuals followed random walk moved at constant speed. In contrast observed data, simulated (with relatively more edge birds) showed greatest relative increase area. This discrepancy between data simulation can be explained mechanistically by differences different sizes. birds leading had faster step travelled further than centre trailing edge. Rates did not vary position. Levels vigilance higher first 10 min males, smaller edges flocks. Thus, upon maintain defensive high vigilance, time, decreases larger expand, suggesting need for reduce competition.