The role of naturally stored food supplies in the winter diet of the boreal Willow Tit Parus montanus

Abstract

The average amount of food that was stored during an autumn by Willow Tits Porus montanus was estimated by sampling hoarding intensities and analysing the energetic contents of the stored items. Measurements of retrieval and losses of the stored food made it possible to calculate how much of the stored food that actually was used by the hoarder. Also the chemical composition of the stored food was analysed, and a comparison of the energy contents of the food eaten with the energy requirements of the birds made it possible to assess the importance of hoarded food in the winter diet. According to the calculations, hoarded food can be assumed to account for almost all food that was consumed during December, whereas it was estimated to constitute around 24% of the food eaten from January to March. During colder winters, with higher energetical stress, it is possible that stored supplies could be more important during this part of the winter, perhaps of the magnitude of 45% of the total food consumed.