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Mortality Patterns in the Isle Royale Moose Population

Michael L. Wolfe
The American Midland Naturalist
Vol. 97, No. 2 (Apr., 1977), pp. 267-279
DOI: 10.2307/2425093
Stable URL: http://www.jstor.org/stable/2425093
Page Count: 13
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Mortality Patterns in the Isle Royale Moose Population
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Abstract

Sex, age and temporal distribution of 439 Isle Royale moose (Alces alces), dying of natural causes from approximately 1950 to 1969, are analyzed. At least 45% of the animals examined had been killed by wolves (Canis lupus). Calves and yearlings comprised 29.3% and 3.5%, respectively, of the wolf-kills, but were underrepresented in relation to their occurrence in the population. A pronounced selectivity for "old" animals was demonstrated with age classes 12-17 years comprising 29.3% of the wolf-kills. As a group, the wolf-kills also showed a significant preponderance of females. Age distribution of moose dying of unknown causes (34.9% of the total sample) differed significantly from that of wolf-kills. Young adults comprised 24.2% of the unknown mortality remains, while "middle-aged" (7-11 years) and old animals accounted for 37.9% and 12.4%. Moose dying of unknown causes showed a highly significant preponderance of males, but age distribution between sexes did not differ statistically. Age distribution among winter wolf-killed moose showed a significant increase of younger animals in the kill during the latter half of the period 1959-69. The role of wolf predation in the regulation of this population is discussed.

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