White-tailed deer (Odocoileus virginianus) exhibit a variety of migration strategies across northern portions of their range. Factors reported as being responsible for migration initiation have shown no consistent pattern. We monitored 186 radiocollared white-tailed deer from 1994 to 1998 in 2 areas of New Brunswick: a southern area with moderate and variable winter climate and a northern area with consistently severe winter climate. We determined that deer in the south contained a large proportion of conditional migrators (individuals that may or may not migrate to winter range in a given year, and may or may not remain until spring), whereas deer in the north consisted almost entirely of obligate migrators (those that annually migrate to winter range for the duration of winter). Occurrence of conditional migration appeared to be a function of climate variability, although distribution of the behavior among individual deer was influenced by migration distance. Initiation of autumn migration in the south was related to snow depth for most deer and represented a response to the proximate cue of the onset of limiting conditions. Autumn migration in the north appeared to be a response to seasonal cues, and the direct influence of snow depth was reduced. Initiation of spring migration in the 2 study areas showed a similar pattern. Migration distance may represent a factor influencing distribution of migrational cues among individual deer within a population. The effect of winter climate variability on deer migration behavior may account for the disparity in behavior reported in the literature. The differences in migration behavior have implications for deer management surveys in northern areas where deer yarding occurs. Managers have assumed that deer observed during winter surveys were on winter range, but this may not be a reasonable assumption in areas with variable winter climates.

Summary1. Demographic analysis is essential in order to determine which factors, such as survival, fertility and other life-history characteristics, have the greatest influence on a population's rate of growth ( λ ). 2. We used life-table response experiments (LTREs) to assess the relative importance of survival and fertility rates for an alpine lagomorph, the collared pika Ochotona collaris , using 12 years (1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003)(2004)(2005)(2006) of census data. The LTRE analysis was repeated for each of three subpopulations within the main study site that were defined by aspect (east, west and south). 3. Across the entire study site, the survival and fertility of adults contributed 35·6 and 43·5%, respectively, to the variance observed in the projected population growth rate, V( λ ), whereas juvenile survival contributed 20·9%. Adult survival and fertility contributed approximately equal amounts for each subpopulation when considered separately, although their rank order varied spatially. 4. Adult survival across the entire site was positively correlated to the Pacific Decadal Oscillation (PDO) with a time lag of 1 year, and was uncorrelated to adult density. The PDO was negatively correlated to the timing of spring snowmelt at our site, implicating the importance of earlier spring conditions and plant phenology on the subsequent winter survival of adults and therefore, population growth. 5. When subpopulations were analysed separately, survivals and fertilities were variously correlated to lagged PDO and adult densities, but the patterns varied spatially. Therefore, the mechanisms underlying V( λ ) can vary substantially over relatively short distances.

For socially hibernating mammals, the effectiveness of huddling as a means of energy conservation should increase with group size. However, group size has only been linked to increased survival in a few hibernating species, and the relative importance of social structure versus winter conditions during hibernation remains uncertain. We studied the influence of winter weather conditions, social group composition, age-structure, and other environmental factors and individual attributes on the overwinter survival of hoary marmots (Marmota caligata) in the Yukon Territory, Canada. Juvenile hoary marmot survival was negatively correlated with the mean winter (November to May) Pacific Decadal Oscillation (PDO) index. Survival in older age-classes was negatively correlated with PDO lagged by 1 year. Social group size and structure were weakly correlated with survival in comparison to PDO. The relationship between winter PDO and survival was most likely due to the importance of snowpack as insulation during hibernation. The apparent response of hoary marmots to changing winter conditions contrasted sharply with those of other marmot species and other mammalian alpine herbivores. In conclusion, the severity of winter weather may constrain the effectiveness of group thermoregulation in socially hibernating mammals.

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The effects of predation risk on foraging behavior often result in a trade-off between obtaining food and seeking shelter and may alter the selectivity of herbivores for individual plant species. We experimentally measured forage selection by a small alpine herbivore, the collared pika (Ochotona collaris (Nelson, 1893)), using a cafeteria-style arrangement of six potential forage species at five levels of predation risk. Contrary to our prediction, haying pikas did not switch preferences for forage species of different nutritional quality as predation risk increased. However, the total amount of forage removed was inversely related to risk, and the addition of cover at treatments of greatest potential risk ameliorated the negative effects of higher predation risk. The reasons for increased preference for poorer quality forage species in 2002 relative to 2000 are currently unknown but may reflect changes in predator abundance, forage quality, or increased competition for limited forage resources.