Individual dispersion and productivity of ptarmigan in relation to their selection of food and cover
Dispersion and productivity of individual ptarmigan Lagopus mutus in North-east Scotland was compared with the food and cover available. Diet was studied by measuring the proportions of foods in faeces. Adults ate mostly shoots of crowberry Empetrum nigrum and heather Calluna vulgaris in late autumn, winter and early spring. In late spring and summer they ate mostly shoots of blaeberry Vaccinium myrtillus, herbs and moss capsules. In spring cocks gradually increased their intake of blaeberry and hens markedly so in April. These rates coincided with the onset of development of the sexes' gonads and breeding behaviour. Chicks ate mostly insects and herbs during their first two weeks, and after six weeks their diet was similar to that of the adults. Territories were on areas of blaeberry heath, springs and exposed rock and not on areas of grass, sedge tall heather and no rock. Mean territory size varied inversely with the number of territories in the total area occupied. 94% of resting birds were within 1m cover, mainly rock, and 81% of foraging birds were within 3m of cover. Chicks pecked faster and walked more slowly when they were close to cover. Ptarmigan foraged mostly in blaeberry heaths and springs with vegetation less than 7cm tall, whereas red grouse Lagopus l. socticus, used heather heaths, mires and grassland with vegetation taller than 7cm.