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Factors affecting th local distribution of blue grouse on a breeding range Elliott, Peter Wayne

Abstract

The dispersion of a population of blue grouse was analyzed using data from a breeding range on east-central Vancouver Island. During the summers of 1959-1962, the locations, densities, habitat preferences, and behaviour of grouse were studied using several habitats with varying densities of vegetation. A removal experiment was performed in different habitats to test the effect of interaction and selection of habitat on the dispersion of males. All adult males and a few yearling males were territorial, and territories were spaced in a near-uniform pattern. Within a given season, males removed from their territories were seldom replaced by other adults, suggesting that no surplus of non-territorial adults was present. About half of the yearling males were prevented from establishing territory by the presence of adults, and these yearlings were attracted to the vicinity of territorial males. The location of territories by newly-adult males did not depend significantly on the number of territories already present, even though the tendency toward uniform spacing was preserved. Comparison with other studies indicated that territory size and possibly the fraction of yearling males in the population were inversely related to the density of males. Females restricted their movements while on the breeding range but were not territorial. No pair-bonds were observed but females stayed near territorial males prior to nesting. After the hatch, the locations of females and broods bore no relation to each other or to the positions of males. Interaction apparently had no effect on breeding numbers. All birds preferred sparse vegetation to dense. When compared to randomly-chosen points, territories were found more often in areas with sparse vegetation, elevated points, and patches of open ground. Within open habitats, nests were usually located where cover by logs, stumps, and ground-level vegetation was high, and cover by dead plants and litter was low. Broods were associated with moist areas and other areas having heavy cover by vegetation at the ground level. Chicks apparently dispersed widely between their first and second summers. In their third summer, males usually returned within one-half mile of the positions they used as yearlings. Once territories were established, the owners returned to them in succeeding summers. Females one year and older showed a fairly accurate return to their previous locations. The dispersion was described somewhat theoretically by considering the summer population to be grouped into two types of aggregations. The first, found in the earlier half of the summer, was caused by the attraction of yearling males and lone females to territorial males. Later, hens with their broods were the dominant groupings. The spacing, movements, and habitat preferences seemed to be adaptations allowing such populations to rapidly exploit new habitats.

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