A Population Study of Ptarmigan (Lagopus mutus) in Scotland

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Abstract
Total counts of ptarmigan present on 500 ha of arctic-alpine plant community were obtained from October to May and sample counts in summer. In five winters when several counts were made, numbers stayed fairly constant from autumn till a sudden decrease of 18-47% in March or April. This decrease mainly involved birds without territories, which were expelled by vigorous territory defense. Mortality (mainly predation) did not limit the spring breeding stock and predation did not appreciably depress breeding production or adult numbers in summer. Spring numbers varied annually from 5-18 birds/100 ha and autumn numbers from 8-43/100 ha. Breeding density locally reached 1 pair per 2 has on the best habitat. There were more cocks than hens during population declines. There was evidence of a population fluctuation once every decade. Breeding success varied annually between 0.1 and 2.5 fully grown young to 1 old bird. Chick losses, mainly in the first week after hatching, were not related to summer weather. Breeding was good in years of increase and early years of peak numbers, but poor in later peak years and years of decline. All the favorite habitat of Empetrum heath, Vaccimium heath and mixed Empetrum-Vaccinium-Calluna heath was occupied by territories every spring, and territory size varied inversely with breeding stocks. Grassland, bogs and heaths dominated by Calluna were not occupied. The breeding stock was not related to the amount of snow cover in winter or the amount in late spring. Ptarmigan were more hostile in years of declining numbers. Food was not measured.

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