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Aspects of social organization and diurnal activity patterns of Californian bighorn sheep (Ovis Canadensis Californiana Douglas 1829) Eccles, Thomas Ross

Abstract

The social organization and diurnal activity patterns of captive California bighorn ewes were investigated from May 1977 to December 1978. Social interactions between ewes were brief in duration and infrequent, relative to bighorn rams. Aggressive interactions (butts) were more common than horn displays. Although a dominance hierarchy was evident in the herd, it was not strongly linear. Age, horn length, and body weight were not shown to be strongly correlated to dominance. The most dominant animals proved to be the most aggressive, initiating more interactions than subordinate animals. The presence of a lamb appeared to improve the social status of some ewes. Dominant status could not be shown to positively affect an animal's diet, activity budget or productivity. The herd's diurnal activity pattern changed considerably on a seasonal basis. The activity pattern was characterized by successive feeding and bedding periods in spring and summer. Activity peaks generally declined in number and increased in duration during the fall and winter periods. The herd's diurnal activity budget also varied seasonally. The proportion of the day devoted to feeding increased with decreasing daylength, although actual daylight grazing times were poorly correlated to daylength. The proportion of the day devoted to bedding was highest in spring and summer, and to a lesser extent, in mid-winter. Actual bedding times were significantly correlated (r = 0.92) to daylength. Both the actual time and proportion of the day devoted to standing, travelling and "other" activities showed only minor seasonal fluctuations. It was shown that poor health in herd members affected activity budgets significantly. Late stages of pregnancy could not be shown to significantly affect activity budgets. Average basal metabolic rates (BMR) and diurnal activity costs were estimated for the herd. Both BMR's and activity costs were higher in spring and early summer than at other times of the year.

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