Robert A. MacArthur

Cardiac and Behavioral Responses of Mountain Sheep to Human Disturbance

Telemetered heart rates (HR) and behavioral responses of mountain sheep (Ovis canadensis canadensis) reacting to human disturbance in the Sheep River Wildlife Sanctuary, southwestern Alberta, were recorded. Cardiac and behavioral responses of sheep (4 ewes, 1 ram) to an approaching human were greatest when the person was accompanied by a dog or approached sheep from over a ridge. Reactions to road traffic were minimal as only 8.8% of vehicle passes elicited HR responses. No reactions to helicopters or fixed-wing aircraft were observed at distances exceeding 400 m from sheep. Responses to disturbance were detected using HR telemetry that were not evident from behavioral cues alone. However, mean duration of the HR response (138.6 sec) was not greater (P > 0.05) than mean period of the behavioral reaction when sheep were alert or withdrawing from harassing stimuli (112.4 sec). Use of HR telemetry in harassment research is discussed. J. WILDL. MANAGE. 46(2):351-358 Survival and optimal use of habitat by individuals demand high levels of vigilance so that stimuli indicating presence of predators, conspecifics, food, or shelter do not go undetected (Dimond and Lazarus 1974). Yet if an animal is excessively aroused, as from human disturbance, the added cost of excitement may interfere with health, growth, and reproductive fitness (Geist 1979:5). Recent studies of free-living birds (Kanwisher et al. 1978) and ungulates (Ward et al. 1976, MacArthur et al. 1979) have revealed that heart rate is a sensitive indicator of arousal, the first stage of an alarm reaction to stress (Jenkins and Kruger 1975). These and other investigations (Thompson et al. 1968, Cherkovich and Tatoyan 1973, Moen et al. 1978) have demonstrated consistent HR responses to disturbing visual or auditory stimuli, often in the absence of overt behavioral changes. Expanding upon earlier work (MacArthur et al. 1979), the present paper integrates cardiac and behavioral observations to better understand how individuals in a population of mountain sheep perceive and respond to environmental perturbations. In view of escalating use of alpine areas by hikers, particular attention is focused on the sensitivity of sheep to approaches by humans (Dunaway 1971). The study also addresses relative merits of HR telemetry and overt behavioral observations as methods for detecting and defining harassment responses in ungulates. Preliminary findings (MacArthur et al. 1979) suggested cardiac responses may persist longer than behavioral reactions, and a quantitative comparison of these 2 indices of disturbance is reported here. We acknowledge the field assistance of D. MacArthur, B. Horejsi, G. Lynch, J. Jorgenson, D. Olsen, and D. Nugent. We thank the technical staff of the Department of Electrical Engineering, University of Calgary, for constructing transmitters and other electronic equipment essential to this study. Cooperation provided by the Alberta Forest Service and Alberta Fish and Wildlife Division is also appreciated. Financial support was proIPresent address: Department of Zoology, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada. J. Wildl. Manage. 46(2):1982 351 This content downloaded from 157.55.39.180 on Mon, 25 Apr 2016 06:15:48 UTC All use subject to http://about.jstor.org/terms 352 RESPONSES OF MOUNTAIN SHEEP TO DISTURBANCE* MacArthur et al. vided by the Natural Sciences and Engineering Research Council of Canada, and by the Foundation for North American Wild Sheep.

Seasonal variation in the microclimate and gas composition of beaver lodges in a Boreal environment

Seasonal changes in the microenvironment of Castor canadensis in the Canadian Shield of southeastern Manitoba, Canada, are described. The construction and occupation of lodges by family groups of beavers provided these animals with year-round access to a thermoneutral microclimate. Between June 1988 and March 1989, air temperatures at sampling sites ranged from −41.4 to 32.4°C, while temperatures recorded from within the chambers of occupied lodges varied from 0 to 35.6°C. Mean monthly chamber temperature consistently exceeded mean monthly air and water temperature. Despite the large metabolic mass of resident animals, lodge occupancy resulted in only limited disturbance to the respiratory gas concentrations inside lodges. The CO2 levels of occupied lodges ranged from 0.03 to 1.8%, with no evidence of seasonal variation in either CO2 accumulation or O2depletion in these shelters. Before freeze-up, the gaseous composition and mean internal temperature of occupied and unoccupied lodges were similar. Following freeze-up, mean CO2 accumulation, O2 depletion, and chamber temperature were all significantly higher in occupied houses. During the open-water season, water temperature accounted for 90% of the variation in chamber temperature of occupied lodges. Following freeze-up, none of the meteorological or physical variables measured were significant predictors of chamber temperature.

Heat increment of feeding and its thermoregulatory benefit in the muskrat (Ondatra zibethicus)

The calorigenic effect of feeding and its potential benefit in defraying thermoregulatory costs and attenuating immersion hypothermia of adult muskrats were investigated. A single session of feeding on aquatic vegetation was sufficient to raise the metabolic rate of muskrats for a period of at least 5 h. The peak postprandial rate of oxygen consumption averaged 1.42 times the level established for fasted animals, and the heat increment of feeding accounted for about 40% of the metabolizable energy intake of muskrats. There was no evidence of a postprandial rise in oxygen consumption of muskrats that entered water at 18–19°C after feeding. In aquatic trials, average and minimum steady-state oxygen consumption rates of fed muskrats were similar to, or even lower than values recorded from fasted animals, implying substitution of heat increment of feeding for thermoregulatory heat production. Our data did not support the hypothesis that heat increment of feeding retards body cooling in water. Net body temperature decline in water was actually higher in fed animals than in fasted controls. However, since previously fed muskrats also entered water at an elevated body temperature, the final body temperature (at 30 min immersion) was similar in all groups. These findings suggest that metabolic heat generated incidental to preimmersion feeding could provide a thermoregulatory benefit to muskrats by reducing the need for active thermogenesis in water.

Thermal Benefits of Huddling in the Muskrat (Ondatra zibethicus)

We examined the energy saving and social interactions associated with winter huddling behavior in the muskrat, Ondatra zibethicus . At air temperatures of −10°C and 0°C, which encompass the lowest microclimate temperatures recorded from winter shelters, the resting metabolic rate of an aggregate of four muskrats averaged 11–14% below that of single animals. The minimal thermal conductance of the grouped animals was reduced by 8–10% over this same temperature range. Our findings suggest that communal nesting confers a modest, but potentially significant metabolic saving to overwintering muskrats.

Body oxygen stores, aerobic dive limits, and the diving abilities of juvenile and adult muskrats (Ondatra zibethicus).

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Seasonal changes in the oxygen storage capacity and aerobic dive limits of the muskrat (Ondatra zibethicus)

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Fasting metabolism and thermoregulatory competence of the star-nosed mole, Condylura cristata (Talpidae: Condylurinae)

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