Wintering swans Cygnus spp. and Coot Fulica atra in the Öresund, South Sweden, in relation to available food recources

Abstract

In connection with the building of a Fixed Link (bridge – artificial island – tunnel) between Sweden and Denmark intensive studies of waterfowl and benthic fauna and flora in the Öresund were undertaken as a part of the Environmental Impact Assessment Study. This paper analysis the occurrences of staging and wintering herbivores (i.e. Mute Swan Cygnus olor and Coot Fulica atra) in relation to available food resources. It was concluded that the proportion of Zostera and Ruppia consumed by the birds during September–March was about 10% of the available standing crop in the autumn or less. During ice-periods large parts of the available feeding areas are covered by ice, and during an extended ice-period in 1995/1996 the calculated food consumption for the ice-free areas was of the same magnitude as the calculated standing crop of food plants.