Autumn food of rock ptarmigan Lagopus muta: the effect of age, sex, year and location

Abstract

We analysed food data for rock ptarmigan Lagopus muta collected during a 10 day period at the end of September and beginning of October 2006–2014 in northeast Iceland or for nine years. The total sample was 679 birds, including 455 juveniles and 224 adults; the annual range was 48–88 birds. To describe the importance of items consumed we used percentage by dry biomass (total 1399 g) and percentage by frequency of occurrence. A total of 80+ species were identified, the most important were Betula nana (27% biomass, 62% frequency), Empetrum nigrum (14%, 63%), Dryas octopetala (11%, 64%), and Salix herbacea (10%, 41%). Important plant parts consumed were berries, woody shoots with buds, buds, catkins, seeds and leaves. Difference in diet, both with respect to species and plant parts consumed, depended on year and altitude of collection site but not on ptarmigan sex, age or sex*age interaction. The only significant age difference observed was that juveniles consumed more seeds and less woody parts than did adult birds. Betula spp. dominated the diet in five years and Salix spp. in four years. Betula and Vaccinium spp. were most important at low and medium elevations but Salix spp. showed an opposite pattern. Berries (E. nigrum and Vaccinium spp.) were the dominant plant parts in the diet for six years and woody parts of Salix and Betula spp. in three years. Berries dominated in the diet at low to medium elevations and woody parts showed an opposite pattern.