We determined diurnal time-activity budgets of Mute Swans (Cygnus olor) at Chesapeake Bay, Maryland, USA with the principal aim of determining intensity of their feeding activity. Although Mute Swan herbivory is believed to contribute to declines in submerged aquatic vegetation (SAV) in the Bay, there is a lack of comprehensive quantitative data indicating the magnitude of feeding activity by Mute Swans. We collected time-activity budgets from May through August 2003 (N = 50 10-minute observation periods) and from March through August 2004 (N = 818). Mute Swans spent more time feeding (38.4%) than in non-foraging activities, including swimming (21.8%), resting (18.4%), self-maintenance (18.6%), agonistic activity (1.7%), and disturbance-induced activities (1.2%). Feeding intensity was not influenced by seasons (spring and summer). Mute Swans foraged more actively during the morning than they did midday. Mute Swans in flocks ( three individuals) spent more time feeding than those in pairs and birds in larger flocks spent more time feeding than those in smaller flocks. Moreover, a recent exclosure study on the Chesapeake Bay indicated that grazing by Mute Swan flocks caused a higher SAV decline than grazing by paired Mute Swans. It is likely that individuals in flocks (especially large ones) pose a greater risk to the SAV in the Bay as compared to those in pairs. Thus, management authorities should seriously consider controlling Mute Swan flocks (especially large ones) in the Bay in addition to pairs.
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Vol. 30 • No. 1