Population Dynamics of Capercaillie in a North-East Scottish Glen

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Abstract
During a nine-year study of Capercaillie almost twice as many female as male chicks were reared, but there were no more hens than cocks in the adult population. Both the proportion of male chicks in later summer each year, and mean brood size, were related to the chicks'' condition in July. Condition was related to the number of days with rain in early June, during and just after hatching. The breeding density of hens each year varied betwen 4.0 and 8.0 km-2 but was related neither to their density in the previous year nor to the production of female chicks in the intervening summer. The best predictive model was simply that breeding densities would return to their mean each year. It was inferred that breeding densities were determined by density-dependent losses and gains involving emigration and immigration. Autumn densities of young and old birds were not related to breeding densities and breeding success, but were inversely related to the proportion of broods which disappeared, and probably emigrated, during the summer.