Ruffed Grouse Winter Roost Site Preference and Influence on Energy Demands

Abstract

We located winter roosts of ruffed grouse (Bonasa umbellus) in Missouri with radiotelemetry and determined roost type preference. Thermostatic energy demands in 4 roost types were measured with a heated taxidermic mount calibrated with metabolic rates of captive grouse. Ruffed grouse preferred to roost in the canopies of eastern red cedar (Juniperus virginiana) and avoided roosting in deciduous cover. Roost sites had higher woody stem densities (9 = 5,494 stems/ha) than random plots (9 = 4,236 stems/ha). We predicted ruffed grouse metabolic rates (? 0.75%), at ambient temperatures (Ta) of -20 to 0 C, from power (P,,,) used by the heated taxidermic mount. Standard operative temperature (T,) was elevated 7.3, 2.6, 2.9, and -0.3 C in snow roosts, cedar tree roosts, cedar ground roosts, and deciduous roosts, respectively, above that at an open site for T, of -20 to 0 C. When wind speed was 3 m/second in the open, T, was elevated a mean of 12.9, 7.0, 6.7, and 2.5 C, in snow, cedar tree, cedar ground, and deciduous roosts, respectively. These increases in Tes resulted in a 33, 19, 18, and 6% reduction in metabolic rate in snow roosts, cedar tree roosts, cedar ground roosts, and deciduous roosts, respectively, from that in the open at -20 to 0 C and 3 m/second wind speed. About 40% of the elevation in T, resulted from reduced convection inside roost sites and 60% from a more favorable radiation balance in roosts. Low coniferous vegetation provided thermal benefits that may be important because snow roosts were rarely available. J. WILDL. MANAGE. 52(3):454-460 Birds show physiological and behavioral adaptations to cold stress. Physiological adaptations include increasing metabolic rate, accumulating fat reserves, acclimatizing, decreasing body temperature, and developing winter plumages. Behavioral adaptations include migrating, selecting micro-climates, changing activity patterns, adjusting posture, and responding as a group (Calder and King 1974). Ruffed grouse exhibit several of these adaptations. Grouse increase their metabolic rate in response to cold (Thompson and Fritzell 1988). Increased energy demands in winter may be met in part by fat reserves accrued during summer and fall (Norman and Kirkpatrick 1984) or by regular feeding (Thomas et al. 1975). Heat loss and energy demands are reduced by a lower than average lower-critical temperature and nocturnal depression in body temperature (Thompson and Fritzell 1988). Grouse reduce heat loss behaviorally through micro-habitat selection (Thomas et al. 1975). Snow roosting is documented in ruffed grouse (Bump et al. 1947, Grange 1948) and other tetraoninae can maintain a thermoneutral microenvironment in snow burrows (Hoglund 1980, Marjakangas et al. 1984). During cold weather, ruffed grouse also use conifer cover (Bump et al. 1947) where radiant temperature is higher (Brander 1965). Optimal winter cover for ruffed grouse in northern forests is provided by young aspen stands with 14,000-20,000 stems/ha, where grouse are relatively safe from predation, deep snow provides roosting cover with thermal benefits, and nearby mature aspens (Populus spp.) provide a winter food resource (Gullion 1977). In the southern portion of their range, grouse are often exposed to cold temperatures, but snow cover is insufficient for snow roosting and aspen is bsent. Grouse must use other foods and rely on vegetative cover to reduce thermostatic demands, increase their food consumption, or use accrued energy reserves. We determined microhabitat preferences of ruffed grouse for nocturnal wirter roost sites in Missouri, near the southern terminus of their range. Thermostatic energy demands and heat loss of grouse roosting in different microhabitats were compared. J. E. Roberts provided valuable assistance with the design and construction of the heated taxidermic mount. D. E. Figert, D. Hoffman, and D. G. Kusmec provided field assistance. M. R. Ryan, T. V. Dailey, and F. L. Thompson reviewed the manuscript. Financial support for this study was provided by the Ruffed Grouse Society, the U.S. Forest Service, and the Missouri Department of Conservation. This is Contribution 10381 of the Missouri Agricultural Experiment Station Project (J. Pap. 189) and the