Diurnal activities and foraging methods of juvenile, parent (adults with young), and non-parent (adults without young) Tundra Swans (Cygnus columbianus) were measured during autumn and spring migration at Long Point, Ontario, to evaluate: 1) age-related differences in activities and feeding methods of family members, 2) potential short-term behavioral costs and benefits of prolonged parent-offspring association, and 3) several predictions based on predation risk and swan social structure. Vigilance of inactive parents and juveniles declined as flock size increased at observation sites. However, other evaluations of vigilance in active (and inactive parent/non-parent) swans and use of risk-prone foraging methods did not support the hypothesis that swans respond to reduced risk of predation resulting from membership in larger flocks. These results may be due to their use of inaccessible aquatic habitats and their large relative size, both of which relate to their lack of natural predators, at staging areas. Both parents and young used sub-surface feeding methods to the same amount, but parents “treadled” more than did juveniles and juveniles “dabbled” more on the surface than did parents. These findings suggest that some degree of resource partitioning exists between parents and young or possibly parents indirectly facilitate feeding activities of their young. Parents were more vigilant and interacted with other social groups more than did juveniles, but their feeding activity was unaffected as both parents and juveniles spent similar time foraging. Time spent vigilant, in intraspecific interactions, and feeding was similar between parents and non-parents. Based on this evidence, parents did not appear to incur short-term behavioral or energetic costs of prolonged association with young. However, both parents and juveniles likely benefited from higher social standing associated with family status or larger family size.
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Vol. 28 • No. 3