We propose a fundamental geographic distribution for the wolverine ( Gulo gulo (L., 1758)) based on the hypothesis that the occurrence of wolverines is constrained by their obligate association with persistent spring snow cover for successful reproductive denning and by an upper limit of thermoneutrality. To investigate this hypothesis, we developed a composite of MODIS classified satellite images representing persistent snow cover from 24 April to 15 May, which encompasses the end of the wolverine’s reproductive denning period. To investigate the wolverine’s spatial relationship with average maximum August temperatures, we used interpolated temperature maps. We then compared and correlated these climatic factors with spatially referenced data on wolverine den sites and telemetry locations from North America and Fennoscandia, and our contemporary understanding of the wolverine’s circumboreal range. All 562 reproductive dens from Fennoscandia and North America occurred at sites with persistent spring snow cover. Ninety-five percent of summer and 86% of winter telemetry locations were concordant with spring snow coverage. Average maximum August temperature was a less effective predictor of wolverine presence, although wolverines preferred summer temperatures lower than those available. Reductions in spring snow cover associated with climatic warming will likely reduce the extent of wolverine habitat, with an associated loss of connectivity.

Understanding population vital rates is fundamental to the evaluation of conservation options for wolverines (Gulo gulo). We estimated survival rates and causes of wolverine mortality in trapped and untrapped populations within montane, boreal, and tundra environments using data from 12 North American radiotelemetry studies conducted between 1972 and 2001. Rates were based on data for 62 mortalities of 239 radiomarked wolverines. Mortalities included 22 wolverines that were trapped or hunted, 3 road or rail killed, 11 that were predated, 18 that starved, and 8 deaths of unknown cause. Annual survivorship rates were estimated for sex and age class using Kaplan-Meier staggered-entry techniques. Survival was substantially lower in trapped (<0.75 for all age-sex classes) than in untrapped (>0.84 for all age-sex classes) populations. Human-caused mortality was mostly additive to natural mortality for wolverines in a management context. Logistic growth rate estimates indicated that trapped populations would decline (λ ≅ 0.88) in the absence of immigration from untrapped populations (λ ≅ 1.06). We recommend a system of spatial harvest controls in northern, continuous populations of wolverines and reduction of harvest along with more spatially explicit conservation measures in southern metapopulations. JOURNAL OF WILDLIFE MANAGEMENT 68(3):493-502

Snowshoe hares (Lepus americanus Erxleben, 1777) fluctuate in 9-10 year cycles throughout much of their North American range. These cycles show large variations in cyclic amplitude and we ask what factors could cause amplitude variation. We gathered data from 1976 to 2012 on hare numbers in the boreal forest of Alaska, Yukon, Northwest Territories, and northern British Columbia to describe the amplitude of hare fluctuations and to evaluate four possible causes. First, weather could cause variation in amplitude via hare reproduction or survival, but this mechanism does not fit our data. Second, bottom-up processes involving forest succession could explain amplitude variation through changes in winter forage availability, but succession is too slow a variable in our study areas. Third, plant defenses entrained by hare over-browsing in one cycle can produce variation in plant quality and quantity in subsequent cycles. A mathematical model suggests this is a possible explanation. Fourth, predator recovery following the cyclic low is inversely related to hare cyclic amplitude, and the existing data are consistent with this mechanism. A standardized regional monitoring program is needed to improve our understanding of cyclic amplitude variation in hares and the possible role of predators and winter foods in affecting amplitude.Résumé : L'abondance des lièvres d'Amérique (Lepus americanus Erxleben, 1777) fluctue selon des cycles de 9-10 ans dans une bonne partie de l'aire de répartition nord-américaine de l'espèce. Ces cycles présentent de grandes variations d'amplitude, et nous nous penchons sur les facteurs qui pourraient causer ces variations. Nous avons recueilli des données de 1976 à 2012 sur le nombre de lièvres dans la forêt boréale de l'Alaska, du Yukon, des Territoires-du-Nord-Ouest et du nord de la Colombie-Britannique afin de décrire l'amplitude des fluctuations des lièvres et d'évaluer quatre causes possibles. Premièrement, si la météo peut causer des variations d'amplitude en agissant sur la reproduction ou la survie des lièvres, ce mécanisme ne concorde pas avec les données. Deuxièmement, des processus ascendants associés à la succession forestière pourraient expliquer les variations d'amplitude par des variations de la disponibilité de nourriture durant l'hiver, mais la succession est une variable qui évolue trop lentement dans les zones étudiées. Troisièmement, les mécanismes de défense des plantes induits par le surbroutement des lièvres durant un cycle peuvent produire des variations de la qualité et de la quantité des plantes durant les cycles subséquents. Un modèle mathématique suggère qu'il s'agit d'une explication possible. Quatrièmement, le rétablissement de prédateurs suivant le creux d'un cycle est inversement relié à l'amplitude du cycle des lièvres, et les données concordent avec ce mécanisme. Un programme de surveillance régionale normalisé est nécessaire pour améliorer la compréhension des variations de l'amplitude des cycles des lièvres et de l'effet éventuel des prédateurs et de la nourrit...

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Arctic and boreal ecosystems are experiencing rapid changes in temperature and precipitation regimes. Subsequent shifts in seasonality can lead to a mismatch between the timing of resource availability and species’ life-history events, known as phenological or trophic mismatch. Although mismatch has been shown to negatively affect some northern animal populations, longer-term impacts across large regions remain unknown. In addition, animals may rely on climate cues during preceding seasons to time key life history events such as reproduction, but the reliability of these cues as indicators of subsequent resource availability has not been examined. We used remote sensing and gridded spatial data to evaluate the effect of climate factors on the reproductive phenology and success of a wide-ranging carnivore, the gray wolf (Canis lupus). We used global positioning system (GPS) location data from 388 wolves to estimate den initiation dates (n = 227 dens within 106 packs) and reproductive success in eight populations across northwestern North America from 2000 to 2017. Spring onset shifted 14.2 d earlier, on average, during the 18-year period, but the regional mean date of denning did not change. Preceding winter temperature was the strongest climatic predictor of denning phenology, with higher temperatures advancing the timing of denning. Winter temperature was also one the strongest and most reliable indicators of the timing of spring onset. Reproductive success was not affected by timing of denning or synchrony with spring onset, but improved during cooler summers and following relatively dry autumns. Our findings highlight a disconnect between climate factors that affect phenology and those that affect demography, suggesting that carnivores may be resilient to shifts in seasonality and yet sensitive to weather conditions affecting their prey at both local and regional scales. These insights regarding the relationship between climate and carnivore demography should improve predictions of climate warming effects on the highest trophic levels.