Winter weather versus group thermoregulation: what determines survival in hibernating mammals?

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.

The role of phenotypic plasticity in responses of hunted thinhorn sheep ram horn growth to changing climate conditions.

When phenotypic change occurs over time in wildlife populations, it can be difficult to determine to what degree it is because of genetic effects or phenotypic plasticity. Here, we assess phenotypic changes over time in horn length and volume of thinhorn sheep (Ovis dalli) rams from Yukon Territory, Canada. We considered 42 years of horn growth from over 50,000 growth measurements in over 8000 individuals. We found that weather explained a large proportion of the annual fluctuation in horn growth, being particularly sensitive to spring weather. Only 2.5% of variance in horn length growth could be explained by an individual effect, and thus any genetic changes over the time period could only have had a small effect on phenotypes. Our findings allow insight into the capacity for horn morphology to react to selection pressures and demonstrate the overall importance of climate in determining growth.

The role of lesser snow geese as nitrogen processors in a sub-arctic salt marsh.

Ammonia volatilization losses from faeces of Lesser Snow Geese were measured during the summer of 1987 on the salt-marsh flats at La Pérouse Bay. Amounts of ammonia volatilized increased with increasing ambient temperature, and ranged from 1.0 to 15.1 mg N per 100 mg of nitrogen present as soluble ammonium ions at the start of the 8-h experiment. Using estimates of faecal deposition reported previously, the annual loss via volatilization was estimated at 0.08 g N m-2, or 7.9% of the nitrogen present in goose faeces. Percent change in soluble ammonium ions in fresh faeces after 8 h ranged from -51.1% to +41.1%, indicating that net mineralization of organic nitrogen occurred in some of the faeces. Microbial respiration of fresh goose faeces increased exponentially with temperature. However, variable rates of net mineralization per unit rate of respiration indicated that the substrate quality affected microbial immobilization and thus net nitrogen mineralization. In feeding experiments, captive goslings grazed different types of vegetation, each with distinctive nutritional qualities. Forage quality had significant effects on goose feeding behavior and subsequent rates of nitrogen mineralization in fresh faeces. Net nitrogen mineralization rates in faeces from geese which grazed the three vegetation types ranged from 1.31 to 4.97 mg NH 4+ -N gDW-1 24 h-1. Because plant growth in this salt marsh is nitrogen-limited, where swards are grazed, mineralization of organic faecal nitrogen represents an essential link in the maintenance of the flow of nitrogen into the sediments and the sustained growth of vegetation at a time when most required by the geese.

Growth responses of arctic graminoids following grazing by captive lesser snow geese.

The effects of grazing by captive goslings of the Lesser Snow Goose on coastal vegetation at La Pérouse By. Manitoba were investigated. Swards of Carex subspathacea, Festuca rubra and Calamagrostis deschampsioides were grazed once for different periods (0-180 min) and regrowth of vegetation determined, based on measurements of standing crop, net above-ground primary production (NAPP) and forage quality (leaf nitrogen content). The amounts of foliage removed from swards of Carex subspathacea increased with the length of the grazing period, but after 44 days of regrowth there were no significant differences in above-ground biomass between control and grazed plots. While the amount of foliage removed by goslings from swards of Festuca rubra increased with the length of the grazing period (except after 150 min of grazing), the increase in biomass following defoliation was similar among treatments. Goslings removed little biomass from swards of Calamagrostis deschampsioides, even when the opportunity for grazing was 180 min. No significant differences in standing-crop or NAPP between grazed and ungrazed plots were detected by the end of summer. Grazing had no significant effect on amounts of nitrogen in leaf tissue of all species, suggesting that faecal nitrogen was not rapidly incorporated into plant biomass within the growing season. Patterns of regrowth of these species are compared to that of Puccinellia phryganodes. An increase in goose numbers in recent years has led to birds foraging on less preferred species, such as Calamagrostis deschampsiodes and Festuca rubra. Their poor nutritional quality and a lack of a rapid growth response following defoliation may explain, in part, the decline in the weight of wild goslings recorded over the last decade.

Isolation and characterization of microsatellite loci for the collared pika (Ochotona collaris) and their cross-amplification in five other Ochotona species.

We developed primers for eight polymorphic microsatellite loci isolated from the collared pika, Ochotona collaris, and also tested nine loci previously developed for the American pika, O. princeps, for use in O. collaris. Forty-six individuals from an O. collaris population in the southern Yukon were genotyped using all 17 loci. The average number of alleles per locus was six and the average observed heterozygosity was 0.59. All loci were tested for use in four Asian pika species and all but two loci amplified reliably in these species.

Social structure and facultative mating systems of hoary marmots (Marmota caligata).

Mate-choice theory predicts different optimal mating systems depending on resource availability and habitat stability. Regions with limited resources are thought to promote monogamy. We tested predictions of monogamy in a social rodent, the hoary marmot (Marmota caligata), at the northern climatic extreme of its distribution. Mating systems, social structure and genetic relationships were investigated within and among neighbouring colonies of marmots within a 4 km(2) valley near Kluane National Park, Yukon, Canada, using 21 microsatellite loci. While both monogamous and polygynous populations of hoary marmots have been observed in the southern reaches of this species' range; northern populations of this species are thought to be predominantly monogamous. Contrary to previous studies, we did not find northern hoary marmot social groups to be predominantly monogamous; rather, the mating system seemed to be facultative, varying between monogamy and polygyny within, as well as among, social groups. These findings reveal that the mating systems within colonies of this species are more flexible than previously thought, potentially reflecting local variation in resource availability.