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Food habits in relation to the ecology and population dynamics of blue grouse. King, Richard Dennis

Abstract

The late spring and slimmer diet of blue grouse on lowland breeding ranges on Vancouver Island was determined by examination of the contents of 875 crops taken from birds collected on 3 study areas in the years 1950 through 1952 and 1957 through 1966. The spring and early summer diet of males was mostly conifer needles, while adult females ate mainly leaf material and flowers during the same period. The food of chicks was mainly invertebrates until the birds reached the age of approximately three weeks, at which time plant material formed the greater portion of the diet. In late summer the diet of both adult and juvenile grouse was primarily fruits and seeds of trailing blackberry, salal, huckleberry, and other plants. Selection of plant foods occurred at the time of ovulation and moult. As a result, the protein and mineral content of the diet was highest during periods of greatest need. No apparent differences in the spring diet of females were found which could be related to poor early survival of chicks, or to a delayed hatch in 1962. The various food types were eaten in similar relative proportions by adult and yearling grouse, and differences in reproductive performance of these two age classes could not be related to the diet of the grouse. The altitudinal migration of blue grouse in late summer and autumn does not appear to be related to the availability or condition of the food supply at the time of departure of the birds.

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