Population regulation in spruce grouse: a working hypothesis

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Abstract
We studied a population of spruce grouse in southwestern Alberta over a period of 10 years. During this time the density of birds in the spring population varied between 10.5 and 19.3 per 100 ha. Changes in density appeared to reflect changes in rates of recruitment to the spring population more than changes in rates of mortality among the members of the established population. Recruitment of yearlings was influenced by the density of adults at the onset of the breeding season as was the number of young surviving to independence. We postulate that these two relationships prevent spring densities varying greatly from year to year: spacing behaviour of adults appears to regulate the spring density of grouse locally by forcing yearlings, in excess of those required to fill vacancies, to disperse; the density of grouse during the breeding season appears to influence inversely the number of juveniles surviving to September and consequently the number of yearlings locally available the following spring.