The importance of birds in the diet of otter Lutra lutra on Shapwick Heath

Abstract

This study investigates the importance of avian species in the diet of Shapwick Heath's otter population. The frequency occurrence of prey items was recorded from spraints collected between July 2006 and January 2007. Bird feathers extracted from otter spraints were investigated under a microscope. Where possible, feathers were identified to species level. The presence of fish scales in spraints was recorded, but not quantified. Bird feathers were recorded in 41% of all spraints, compared with 4.6% on Slapton Ley in 1981 and 4.7% on the Somerset Levels in 1975. The highest proportion of bird feathers was recorded in July 2006, at 61%. Ralliformes were more frequently recorded than any other family of birds. Coot Fulica atra L. were more frequently recorded then any other species; 15 spraints were found to contain coot feathers. Mallard Anas platyrhynchos feathers were recorded in six spraints. Cormorant Phalacrocorax carbo feathers were found in three spraints and Water rail Rallus aquaticus feathers were found in two spraints. Pintail Anas acuta, teal Anas creca, moorhen Gallinula chloropus and little grebe Tachybaptus ruficollis feathers were found in one spraint each. Two spraints contained feathers from both mallard and coot, respectively. The high proportion of birds in the otter's diet, in comparison with past studies suggests that otters are substituting birds for part of their traditional diet of fish. It is recommended that studies into the nature of the fish stock and the development of the aquatic ecosystem on Shapwick Heath be undertaken.