A change of moulting site for Mute Swans Cygnus olor in Gloucestershire

Abstract

The distribution and activities of moulting Mute Swans were monitored in July and August] 99]at two sites in the Severn Vale, Gloucestershire; the pools of Slimbridge Wildfowl & WetlandsCentre, and Frampton gravel pits some 5 km northeast of Slimbridge. The number of birdsmoulting at Slimbridge has increased rapidly since ]987, with a corresponding decrease innumbers at Frampton and, by 1992, only two breeding pairs remained to moult at the Frampton site. Differences in activity patterns of moulting swans at the two sites in 1991 indicated thecauses underlying this change in distribution. Provision of a concentrated food supply in shallowpools at S/imbridge, together with low levels of disturbance, allowed birds there to spendsignificantly less time swimming and significantly more time in comfort activities such aspreening than those at Frampton. The percentage of time spent feeding was the same at bothsites (42%) but the mode of feeding differed significantly, with more grazing and less upending at Slimbridge.
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