Diet composition of three swan species (Mute Swan, Whooper Swan and Bewick's swan) in the eastern part of the Gulf of Finland based on fecal analysis

Abstract

The quality of swans' nutrition at spring migration stopovers is important for their successful breeding. The aim of this study was to increase our understanding of the differences in nutrition of different swan species when sharing the same habitat. Microscopic analysis of Cygnus olor, C. cygnus, and C. bewickii feces collected in the eastern part of the Gulf of Finland in February-April 2014-2019 was performed. We measured food preferences of the three swan species using non-metric multidimensional scaling (NMDS). The width and overlap of dietary niches were also calculated. The diet of C. olor consists almost entirely of soft submerged aquatic vegetation, mainly macroalgae. Samples of the other two species except macroalgae contained large amounts of young shoots and roots of rigid semi-submerged and coastal vegetation. The dietary niche of C. cygnus is the most isolated because it is dominated by thick rhizomes of Phragmites australis, which are hardly used by other swan species. The diet of Bewick’s swans was similar in many respects to that of the Mute swan, but Bewick’s swans much more often preferred vegetative parts of submerged and semi-submerged plants, such as Stuckenia pectinata, Potamogeton perfoliatus, Sparganium sp., Nuphar lutea, and others.