Mate fidelity in swans: an interspecific comparison

Abstract

Abstract Of the three swan species that occur in Britain, the Bewick’s and Whooper Swans are migratory and the Mute Swan resident throughout the year. The Bewick’s Swan Cygnus columbianus bewickii (see drawing above) breeds on tundra in the Russian arctic, and birds from the western population fly some 4000 km each autumn to wintering sites located primarily in the Netherlands, Britain, and Ireland. British-wintering Whooper Swans Cygnus cygnus, on the other hand, are predominantly from the Icelandic breeding population, and have a comparatively short migratory journey of some 800 km between the breeding and wintering grounds. They nest in a variety of habitats ranging from lowland marshes, amidst areas of intensive farming, to upland sites, where pools and lakes in the glacial moraine support aquatic vegetation, thus providing a food supply for the birds. Differences between Bewick’s and Whooper Swans in the timing of their arrival and departure in Britain each season reflect the different migratory distances undertaken; Whooper Swans generally return to their wintering sites earlier than the Bewick’s Swans in autumn, and leave later in the spring. In Britain the Mute Swan Cygnus olor is very sedentary; only some 3 % of individuals move more than 100 km from their natal area (Birkhead and Perrins 1986). It occupies a wide range of waters including ponds, rivers, and gravel pits, and often frequents urban areas.