We evaluated the abilities of 6 infrared‐triggered camera systems (TrailMaster 1500, TrailMaster 500, Buckshot RTV, Buckshot Scout, CamTrakker, and DeerCam) to detect 3 sizes of animal models at 2 heights above ground and from 3 distances. We also determined the size of the infrared detection zone and the relative sensitivity of different passive camera systems. All camera systems tested had a detection zone that was narrow in the vertical dimension (3–7°). Except for the TrailMaster 500, all systems also had a detection zone that was narrow in the horizontal dimension (<10°). Sensitivity varied among camera systems. Most performed well at default or high sensitivities; the CamTrakker and the Buckshots set at highest sensitivity produced the most detections. All systems except the Buckshot RTV performed better at lower ambient temperatures. We review technical aspects of infrared‐triggered photography and recommend how researchers can improve their success in detecting animals by selecting the appropriate system for their study area and target species and by careful placement and precise alignment of camera units in the field.

We examined maternal energy expenditure in Rocky Mountain bighorn sheep to test the hypothesis (Trivers and Willard 1973) that individual sons in polygynous mammals should obtain a larger maternal subsidy. In accord with theory, males weighed more at birth (an index of relative prenatal expenditure), tended to suckle more between 40 and 100 days of age (an index of relative postnatal expenditure) and imposed greater delays on their mothers' return to estrus in the subsequent breeding season (an index of relative total preweaning expenditure). Mothers rather than offspring appeared to have primary control over postnatal expenditure. The effect of maternal reproductive effort on return to estrus was cumulative over a period of 3-5 years so that ewes making relatively large expenditures gave birth progressively later. Ewe and lamb mortality was associated with late conception in the previous rut. Thus, differential reproductive effort by ewes in this population appeared to entail a fitness cost involving reductions in both offspring and maternal survivorship.

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Survival of lambs in the population of bighorn sheep (Ovis canadensis) on the National Bison Range, Montana, was less than 25% during 1983 and 1984. Sixty-seven percent of lamb mortality occurred within 3 days of birth; ewe behaviour and recovered remains indicated that coyotes likely accounted for most of the mortality. Herd history, calculated inbreeding coefficients, and the observation of several small, weak lambs implied that inbreeding depression, while probably not a major factor in lamb mortality, may have predisposed some lambs to predation. Lamb production was high (88–96%); in spite of high mortality, population numbers were stable.

With 4 figures in the text)Female bighorn sheep were studied over a 27-month period to quantify linearity and stability of social rank; expression of behaviour as a function of rank; development of rank relationships; and reproductive correlates of rank. Females exhibited a stable, non-linear hierarchy that correlated strongly with age. Dominant females used proportionally more threats, whereas subordinates used more subordinance patterns. Females integrated into the hierarchy at 1-2 years of age and then fought their way to high social status. Dominant and subordinate females did not differ in prenatal maternal investment, but dominant females nursed lambs at higher rates, and were more likely than subordinates to nurse alien lambs after their own lamb died.