Seasonal changes in crop content of the Svalbard ptarmigan Lagopus mutus hyperboreus

Abstract

Crop contents of Svalbard Ptarmigan have been examined. For chicks younger than 25 days the crops contained almost exclusively bulbils of Polygonum viuiparum. High incidence of this food item was also found in crops from adult birds during late summer and autumn (July-October). Midwinter (November- February) crops contained a mixture of plant species dominated by herbs like Saxifraga oppositifolia and S. cespitosa, but with a significant contribution from Salk polaris. The proportion of S. polaris increased throughout the winter and became highly dominant in spring (May-June). During all seasons the birds ingested plant parts of high nutritional value. The change in crop content from P. viuiparum to S. polaris via different herbs was associated with a decrease in the content of crude protein from 20-25% in July- August to about 16% in March-April, and a corresponding increase in crude fibre from about 10% to about 15%. The content of inorganic constituents (P. Mg, Ca, K, Na) varied insignificantly with season and was fairly high.