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This study was designed to test the hypothesis that the level of summer mortality in young blue grouse is determined by the condition of the hen, as a reflection of her summer range, and that this mortality, in turn, determines the level of subsequent autumn and spring densities.Early mortality was studied in a series of field and aviary comparisons of chicks on, or from, two areas of Vancouver Island that were in different stages of vegetative succession following logging and burning. No differences were found in the survival of young between areas, but differences were found between years. There were always sufficient young produced into autumn to replace annual losses in the breeding population.The major conclusions are: (1) early mortality varied between years but not between different habitat types or areas with different breeding densities, (2) variations in early mortality between years appeared to be a result of undetermined parental influences which acted before laying, and (3) this mortality did influence autumn numbers, but was not involved in the regulation of spring numbers.

Determination of age of pikas (Ochotona princeps Richardson) by counting adhesion lines in periosteal bone of the lower jaw is described. Pikas attain a maximum age of at least 7 years in Alberta and Colorado. Estimated yearly losses of adults did not differ significantly between sexes, years of the study, or among collecting areas, and averaged 46%. Age-specific rates of mortality were greatest in the 0–1 and 5–7 year age groups and the general mortality pattern was similar to those reported for other mammals.

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