Winter bioenergetics of Rocky Mountain bighorn sheep

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Abstract
Changes in voluntary dry matter intake, body weight and resting metabolic rates at 10.degree. and -10.degree. C were measured in 4 adult Rocky Mountain bighorn sheep [Ovis canadensis] from Oct. to May. Voluntary intake in mid-Feb. decreased to 0.55 of that in mid-Oct. Body weights increased until Jan. after which stasis or slight declines occurred. Resting metabolic rate at 10.degree. C fluctuated without a consistent pattern over winter. Resting metabolic rates at -10.degree. C were lowest in Feb. and highest in May. The lower critical temperatures of fed animals in winter pelage were below -20.degree. C. As temperatures were lowered from -20.degree. to -30.degree. C, metabolic rates increased 1.37 to 1.39-fold. Wind speeds from 4-8 m/s increased metabolic rates only at temperatures below -20.degree. C.