Territory Size, Mating Status, and Individual Survival of Males in a Fluctuating Population of Willow Ptarmigan

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Abstract
Mean territory size decreased gradually from 7.5 ha in 1979 to 4.3 ha in 1982 and increased sharply to 7.8 ha in 1983. During the same period, mean territory size was inversely proportional to breeding density in the current spring and to chick production in the preceding summer. The fluctuation in mean territory size was predominantly affected by changes in the intruder pressure caused by young cocks, but was also associated with a change in the aggressive state of territorial cocks. Mean territory size of young and old cocks did not differ significantly. Mated cocks had significantly larger territories, weighed significantly more and survived better than unmated cocks. Some indirect evidence for the existence of a surplus population was found.