Mute swan habitat preferences
Wednesday 16th July 2014
With its white plumage, orange bill and large size, the mute swan (Cygnus olor) is easy to spot. Native to Britain and temperate regions of Europe and western Asia, mute swans are a common sight on a variety of habitats including rivers, lakes, ditches and fields. In a recent study we used repeated field surveys and an electivity index to quantify the habitat preferences of the mute swan in a chalk river catchment. We carried out repeated surveys of the River Frome catchment (Dorset, UK) every month (2010) or two months (2009). We surveyed all habitats within 500 metres of the main river channel between Maiden Newton, a headwater site in the upper reaches of the catchment, and the estuary at Poole Harbour. This landscape offers a mosaic of different habitats including rivers, lakes, ditches, estuary, and pasture and arable fields. For each of these six habitats we calculated an electivity value, taking into account the number of swans using that habitat, and the total area of that habitat. A positive value indicated that swans had a preference for that habitat, whilst a negative value indicated that swans were avoiding that habitat. We found that both season and social grouping (territorial vs non-territorial) affected swan habitat preferences. Non-territorial swans, such as juveniles and non-breeding adults, preferred pasture fields in winter and spring. These low-lying fields of ryegrass flood in winter and provide a good quality feeding habitat. However, during summer and autumn the habitat preferences were different, with river habitat being preferred. In contrast, territorial swans preferred river and lake habitats throughout the year. These habitat preferences were consistent between years. We have undertaken further research to try to understand these habitat preferences in detail.
The electivity index used here could be used to calculate habitat preferences across a landscape for any species, not just swans. This study is part of a larger project examining swan interactions with aquatic plants in shallow rivers, and will help us understand how swan resource use varies across the landscape.
For more information please see the published paper:
Wood, K.A., Stillman, R.A., Coombs, T., McDonald, C., Daunt, F. & O’Hare, M.T. (2013). The role of season and social grouping on habitat use by mute swans (Cygnus olor) in a lowland river catchment. Bird Study, 60: 229-237.