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The ecology and distribution of ptarmigan in western North America Weeden, Robert Barton

Abstract

The three purposes of this study were to summarize the important features of the habits and life history of ptarmigan (Lagopus lagopus, L. mutus and L. leucurus), to describe and compare some places in which each species breeds in western North America and to propose some factors which may influence the distribution of the three species. Ptarmigan are herbivores which show little evidence of important specific differences in diet. All known populations of leucurus and many populations of lagopus and mutus are non-migratory, although seasonal vertical movements may occur. However, some northern populations of the latter two species show annual migratory movements presumably based on food scarcity. Male ptarmigan defend areas of ground in the breeding season. Ptarmigan are monogamous and produce only one brood each year. The onset of egg-laying seems to coincide with the initial disappearance of snow from potential nesting sites. In spring each species selects areas in which to breed. Where three species are present on the same mountain, the ranges of lagopus, mutus and leucurus are progressively further above timberline. The segregation seems to be based primarily on features of vegetation form and terrain. Estimates of height and coverage were used to describe vegetation in places used by ptarmigan. L. lagopus established territories and nested where clusters of shrubs from 3-6 feet in height alternated with openings where plants were less than 1 foot tall (or, if taller, very sparse); the vegetation was relatively luxuriant, with a wide variety of species. L. mutus occupied a zone of tundra similar in vegetation structure but with lower shrubs and a greater proportion of herbaceous vegetation. L. leucurus showed a preference for shrubless alpine areas where plants rarely exceeded 1 foot in height, and where ledges, boulder fields and coarse screes provided crevices for shelter. The available evidence suggests that psychologic factors may control habitat selection. It is proposed that each ptarmigan responds to a set of visual cues which is peculiar to that species. As a result, the range boundaries of a particular population may be set by the occurrence of the features of the environment which are important visual cues. Through such habitat selection, each species of ptarmigan may choose automatically the environment to which it is best adapted.

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