Dall Sheep Demography in McKinley Park and a Reevaluation of Murie's Data

Murphy, Edward; Whitten, Kenneth

Population numbers, age-sex composition, and the male age structure of Dall sheep (Ovis dalli) were studied in Mount McKinley National Park, Alaska, in the summer of 1972. Age of living males was estimated either by counting horn annuli from photographs taken in the field or, if annuli could not be discerned in the photographs, on the basis of horn size. The correlation of age with horn size first was determined for the former group by multiple regression analysis; the resultant equation then was used to estimate age in the latter group. Composition ratios and the sample of males whose ages were estimated were used to establish the age structure of the living male segment of the population. The results demonstrated that the age structure had not been stationary over the past several years. Differences in numbers in each age-class were due to marked variability in initial size and in mortality rates of the cohorts comprising the population. Quantitative analysis of skull data collected by A. Murie from 1937 to 1941, which have been used widely in the construction of life tables, demonstrated that the age structure was not stationary during the period the skulls accumulated. Analyses of changes in population size and of variation in natality rates suggested that the pattern of the life tables was due not only to variation in age-specific survivorship but also to marked variation in initial size of the actual cohorts comprising the samples. Natality was inversely correlated with snowfall and density. First-year survivorship was not correlated with natality rate, indicating that the factors affecting these demographic parameters varied substantially from year to year.

Dall Sheep Demography in McKinley Park and a Reevaluation of Murie's Data

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