Winter Survival of Wild Turkey Females in Central Minnesota

Abstract: There is interest in expanding eastern wild turkey (Meleagris gallopavo silvestris) populations north of their current range. We hypothesized that winter survival and food availability are primary determinants in setting the northern extent of wild turkey distribution. To test our hypothesis, we translocated wild turkey females north of their present range into central Minnesota, USA, and compared survival in areas with supplemental food in the form of corn food plots versus areas with no supplemental food. During 2 winters with below-average snow, winter survival was higher for females with supplemental food. In one winter with above-average snow depths, survival was extremely low even with supplemental food. Supplemental food could augment survival during mild winters if wildlife managers arrange with farmers to, annually, retain standing corn near roosting habitat, but food plots may only partially offset effects of deep snow. Managers should critically evaluate northern habitats, long-term costs of sustained feeding, and potential outcomes of concentrating animals and introducing wild animals into new ecosystems. Winter survival may delimit the northern range of wild turkeys, though annual survival rates may also be important and need further research.     

Precipitation and Reproduction are Negatively Associated with Female Turkey Survival

Understanding how reproductive tradeoffs act in concert with abiotic elements to affect survival is important for effective management and conservation of wildlife populations, particularly for at-risk or harvested species. Wild turkeys (Meleagris gallopavo) are a high-interest species for consumptive and non-consumptive uses, and female survival is a primary factor influencing turkey population dynamics. We radio-tracked and collected survival data on 140 female Merriam's wild turkeys (M. g. merriami) in the northern Black Hills, South Dakota, USA, 2016–2018. We developed and compared a set of candidate models to evaluate how nest incubation, brood rearing, and precipitation could be associated with female survival. Increased time spent incubating was associated with reduced female survival. Additionally, daily precipitation was associated with reduced survival of incubating females. Seasonal survival was lowest during spring and winter. A female that did not incubate a nest was predicted to have a higher rate of annual survival (0.53, 85% CI = 0.48–0.59) than a female that incubated a single nest (0.47, 85% CI = 0.42–0.53). Despite the relative proximity of population segments, we estimated that annual survival for nesting and non-nesting females was lower in the northern Black Hills compared to annual female survival in the southern Black Hills, underscoring the need for region-specific data when possible. © 2020 The Wildlife Society.     

Gobbling across landscapes: Eastern wild turkey distribution and occupancy–habitat associations

Extensive restoration and translocation efforts beginning in the mid‐20th century helped to reestablish eastern wild turkeys (Meleagris gallopavo silvestris) throughout their ancestral range. The adaptability of wild turkeys resulted in further population expansion in regions that were considered unfavorable during initial reintroductions across the northern United States. Identification and understanding of species distributions and contemporary habitat associations are important for guiding effective conservation and management strategies across different ecological landscapes. To investigate differences in wild turkey distribution across two contrasting regions, heavily forested northern Wisconsin, USA, and predominately agricultural southeast Wisconsin, we conducted 3050 gobbling call‐count surveys from March to May of 2014–2018 and used multiseason correlated‐replicate occupancy models to evaluate occupancy–habitat associations and distributions of wild turkeys in each study region. Detection probabilities varied widely and were influenced by sampling period, time of day, and wind speed. Spatial autocorrelation between successive stations was prevalent along survey routes but was stronger in our northern study area. In heavily forested northern Wisconsin, turkeys were more likely to occupy areas characterized by moderate availability of open land cover. Conversely, large agricultural fields decreased the likelihood of turkey occupancy in southeast Wisconsin, but occupancy probability increased as upland hardwood forest cover became more aggregated on the landscape. Turkeys in northern Wisconsin were more likely to occupy landscapes with less snow cover and a higher percentage of row crops planted in corn. However, we were unable to find supporting evidence in either study area that the abandonment of turkeys from survey routes was associated with snow depth or with the percentage of agricultural cover. Spatially, model‐predicted estimates of patch‐specific occupancy indicated turkey distribution was nonuniform across northern and southeast Wisconsin. Our findings demonstrated that the environmental constraints of turkey occupancy varied across the latitudinal gradient of the state with open cover, snow, and row crops being influential in the north, and agricultural areas and hardwood forest cover important in the southeast. These forces contribute to nonstationarity in wild turkey–environment relationships. Key habitat–occupancy associations identified in our results can be used to prioritize and strategically target management efforts and resources in areas that are more likely to harbor sustainable turkey populations.     

Seedling responses to decreased snow depend on canopy composition and small‐mammal herbivore presence

Winter is becoming warmer and shorter across the northern hemisphere, and reductions in snow depth can decrease tree seedling survival by exposing seedlings to harmful microclimates. Similarly, herbivory by small mammals can also limit the survival and distribution of woody plants, but it is unclear whether winter climate change will alter small‐mammal herbivory. Although small‐scale experiments show that snow removal can either increase or decrease both soil temperatures and herbivory, we currently lack snow‐removal experiments replicated across large spatial scales that are needed to understand the effect of reduced snow. To examine how winter herbivory and snow conditions influence seedling dynamics, we transplanted Acer saccharum and Tsuga canadensis seedlings across a 180 km latitudinal gradient in northern Wisconsin, where snow depth varied seven‐fold among sites. Seedlings were transplanted into one of two herbivory treatments (small‐mammal exclosure, small‐mammal access) and one of two late‐winter snow removal treatments (snow removed, snow unmanipulated). Snow removal increased soil freeze‐thaw frequency and cumulative growing degree‐days (GDD), but the magnitude of these effects depended on forest canopy composition. Acer saccharum survival decreased where snow was removed, but only at sites without conifers. Excluding small mammals increased A. saccharum survival at sites where the small‐mammal herbivore Myodes gapperi was present. Excluding small mammals also increased T. canadensis survival in plots with < 5 cm snow. Because variation in canopy composition and M. gapperi presence were important predictors of seedling survival across the snow‐depth gradient, these results reveal complexity in the ability to accurately predict patterns of winter seedling survival over large spatial scales. Global change scenarios that project future patterns of seedling recruitment may benefit from explicitly considering interactions between snow conditions and small‐mammal winter herbivory.     

Change in winter snow depth and its impacts on vegetation in China

Snow on land is an important component of the global climate system, but our knowledge about the effects of its changes on vegetation are limited, particularly in temperate regions. In this study, we use daily snow depth data from 279 meteorological stations across China to investigate the distribution of winter snow depth (December–February) from 1980 to 2005 and its impact on vegetation growth, here approximated by satellite‐derived vegetation greenness index observations [Normalized Difference Vegetation Index (NDVI)]. The snow depth trends show strong geographical heterogeneities. An increasing trend (>0.01 cm yr^?1) in maximum and mean winter snow depth is found north of 40°N (e.g. Northeast China, Inner Mongolia, and Northwest China). A declining trend (?1) is observed south of 40°N, particularly over Central and East China. The effect of changes in snow depth on vegetation growth was examined for several ecosystem types. In deserts, mean winter snow depth is significantly and positively correlated with NDVI during both early (May and June) and mid‐growing seasons (July and August), suggesting that winter snow plays a critical role in regulating desert vegetation growth, most likely through persistent effects on soil moisture. In grasslands, there is also a significant positive correlation between winter snow depth and NDVI in the period May–June. However, in forests, shrublands, and alpine meadow and tundra, no such correlation is found. These ecosystem‐specific responses of vegetation growth to winter snow depth may be due to differences in growing environmental conditions such as temperature and rainfall.     

Lemming winter habitat choice: a snow-fencing experiment

The insulative value of early and deep winter snow is thought to enhance winter reproduction and survival by arctic lemmings (Lemmus and Dicrostonyx spp). This leads to the general hypothesis that landscapes with persistently low lemming population densities, or low amplitude population fluctuations, have a low proportion of the land base with deep snow. We experimentally tested a component of this hypothesis, that snow depth influences habitat choice, at three Canadian Arctic sites: Bylot Island, Nunavut; Herschel Island, Yukon; Komakuk Beach, Yukon. We used snow fencing to enhance snow depth on 9-ha tundra habitats, and measured the intensity of winter use of these and control areas by counting rodent winter nests in spring. At all three sites, the density of winter nests increased in treated areas compared to control areas after the treatment, and remained higher on treated areas during the treatment. The treatment was relaxed at one site, and winter nest density returned to pre-treatment levels. The rodents’ proportional use of treated areas compared to adjacent control areas increased and remained higher during the treatment. At two of three sites, lemmings and voles showed significant attraction to the areas of deepest snow accumulation closest to the fences. The strength of the treatment effect appeared to depend on how quickly the ground level temperature regime became stable in autumn, coincident with snow depths near the hiemal threshold. Our results provide strong support for the hypothesis that snow depth is a primary determinant of winter habitat choice by tundra lemmings and voles.     

White-Tailed Deer,Weather and Predation: a New Understanding of Winter Severity for Predicting Deer Mortality

Variation in white-tailed deer (Odocoileus virginianus) mortality during winter affects population growth in cold climates. Across the northern extent of their range, mortality increases with colder temperatures and snow. Few studies have examined the relationships between winter conditions and deer mortality, and no studies have concurrently studied this relationship for different ages of deer across multiple years and landscapes. We used recently developed cause-specific mortality models to evaluate temporal and age-class variation in deer mortality in farmland areas and compared to published results from forest areas in Wisconsin, USA, from 2011–2014. We then used temporally varying snow and temperature covariates to predict mortality trends using telemetry information from 860 deer. Cause-specific mortality in the farmland varied by age and year, similar to results from previous research in the forest. Human-related mortality was the leading cause of mortality in the farmland during most years and ranged from 4.3% to 10.3% for juveniles and 3.6% to 9.1% for adults from 2011–2014. Very little predation occurred in the farmland, and this differed from previous research in the forest where predation was the leading cause of mortality. During more severe winters (2013 and 2014), other mortality, usually associated with starvation, was the leading cause of mortality for juveniles in the farmland but not adults. In the forest, we found support for saturating effects of accumulated snow depth days >30.5 cm and accumulated temperature days >0°C on mortality. We also found support for the relationship of mortality with accumulated temperature days >0°C in the farmland but no relationship with snow depth. Deer tolerate sustained cold temperatures, but the timing of winter to spring transition is more important for deer survival in both forested and agricultural areas. In the absence of empirical survival information, managers can use our model to predict annual winter effects on deer survival, which can provide improved inference compared to traditional winter severity indices. Our results suggest changes in predator abundance may have minor influence on overwinter survival compared to winter weather. Based on mortality estimates from previous research, the highest predation rates on juvenile deer in the forest occurred when wolf (Canis lupus) counts were lowest and when wolf abundance was highest, juvenile deer predation rates were lowest. © 2021 The Wildlife Society.     

On the distributional limits of the lucidophyllous forest in the Japanese Archipelago

The distribution of the lucidophyllous forest and its transition to the summergreen broadleaf forest were studied in relation to such environmental factors as temperature and precipitation. The distribution is primarily affected by low temperatures during winter and secondarily by precipitation and sea wind. The upper and northern limits of the forest most closely correlated with the coldness index within four thermal indices. Because of much snow, the forest is more suppressed at a lower altitude in the region with high snowfall than in other regions. The area at its upper limit is dominated by the evergreenQuercus forest while the area at its northern limit is occupied by thePersea forest. Moreover, CI values in these distributional limits are significantly different. This phenomenon appeared to result from the resistance ability of dominant lucidophyllous trees not only to the thermal conditions but also to sea wind. In both the region with high snowfall and the region with high rainfall there is a zone where the evergreenQuercus forest overlaps theFagus crenata forest. In contrast, in the region with little rainfall, these two forests do not overlap but form a gap dominated by forests such as theFagus japonica forest. Thus, precipitation factors largely affect the altitudinal forest zones in Japan.     

Evaluating the Mechanisms of Landscape Change on White-Tailed Deer Populations

Understanding how landscape change influences the distribution and densities of species, and the consequences of these changes, is a central question in modern ecology. The distribution of white-tailed deer (Odocoileus virginianus) is expanding across North America, and in some areas, this pattern has led to an increase in predators and consequently higher predation rates on woodland caribou (Rangifer tarandus caribou)—an alternate prey species that is declining across western Canada. Understanding the factors influencing deer distribution has therefore become important for effective conservation of caribou in Canada. Changing climate and anthropogenic landscape alteration are hypothesized to facilitate white-tailed deer expansion. Yet, climate and habitat alteration are spatiotemporally correlated, making these factors difficult to isolate. Our study evaluates the relative effects of snow conditions and human-modified habitat (habitat alteration) across space on white-tailed deer presence and relative density. We modeled deer response to snow depth and anthropogenic habitat alteration across a large latitudinal gradient (49° to 60°) in Alberta, Canada, using motion-sensitive camera data collected in winter and spring from 2015 to 2019. Deer distribution in winter and spring were best explained by models including both snow depth and habitat alteration. Sites with shallower snow had higher deer presence regardless of latitude. Increased habitat alteration increased deer presence in the northern portion of the study area only. Winter deer density was best explained by snow depth only, whereas spring density was best explained by both habitat alteration and the previous winter's snow depth. Our results suggest that limiting future habitat alteration or restoring habitat can alter deer distribution, thereby potentially slowing or reversing expansion, but that climate plays a significant role beyond what managers can influence. © 2020 The Wildlife Society.     

Influence of Density and Climate on Population Dynamics of a Large Herbivore Under Harsh Environmental Conditions

ABSTRACT Dynamics of herbivore populations can be influenced both by density-dependent processes and climate. We used age-at-harvest data for adult female white-tailed deer (Odocoileus virginianus) collected over 23 years to estimate survival and reproduction by age class and to identify effects of environmental factors. The study population was located on Anticosti Island (QC, Canada), at the northern limit of the species' range; the population was at high density, and the landscape had scarce forage and abundant snow during winter. Despite severe environmental conditions, population growth apparently increased during the study; adult survival was similar to other populations, although reproduction appeared lower. Winter severity was not related to survival, but density affected adult female survival. Density at estrus was the main factor influencing reproduction of 2- and 3–4-year-olds and also affected reproduction of prime-aged females (5–9-yr-olds), but not of older females. Reproductive rate of younger females was influenced by environmental conditions in autumn, such as high density or snow conditions that limited forage availability. Reproductive success of 5–9- and ≥10-year-old females appeared dependent on spring conditions favoring high-quality forage, probably through effects on neonatal survival. Relative to other studies on northern ungulates, demographic processes in our study appeared to be more affected by autumn and spring climate, in addition to population density, than by winter climate. We thus propose that population density, as well as autumn and spring climate, should be considered in management strategies. Harvest data offered a unique opportunity to study forest ungulates, for which individual monitoring is rarely possible.     

Decrease in winter respiration explains 25% of the annual northern forest carbon sink enhancement over the last 30 years

Aim Winter snow has been suggested to regulate terrestrial carbon (C) cycling by modifying microclimate, but the impacts of change in snow cover on the annual C budget at a large scale are poorly understood. Our aim is to quantify the C balance under changing snow depth. Location Non‐permafrost region of the northern forest area. Methods Here, we used site‐based eddy covariance flux data to investigate the relationship between depth of snow cover and ecosystem respiration (R_eco) during winter. We then used the Biome‐BGC model to estimate the effect of reductions in winter snow cover on the C balance of northern forests in the non‐permafrost region. Results According to site observations, winter net ecosystem C exchange (NEE) ranged from 0.028 to 1.53 gC·m^?2·day^?1, accounting for 44 ± 123% of the annual C budget. Model simulation showed that over the past 30 years, snow‐driven change in winter C fluxes reduced non‐growing season CO₂ emissions, enhancing the annual C sink of northern forests. Over the entire study area, simulated winter R_eco significantly decreased by 0.33 gC·m^?2·day^?1·year^?1 in response to decreasing depth of snow cover, which accounts for approximately 25% of the simulated annual C sink trend from 1982 to 2009. Main conclusion Soil temperature is primarily controlled by snow cover rather than by air temperature as snow serves as an insulator to prevent chilling impacts. A shallow snow cover has less insulation potential, causing colder soil temperatures and potentially lower respiration rates. Both eddy covariance analysis and model‐simulated results show that both R_eco and NEE are significantly and positively correlated with variation in soil temperature controlled by variation in snow depth. Overall, our results highlight that a decrease in winter snow cover restrains global warming as less C is emitted to the atmosphere.     

Winter severity or supplementary feeding—which matters more for wild boar?

During recent decades, wild boar have successfully colonised areas previously believed to be unsuitable for the species. Estonia lies close to the northern limit of the species range, and mast foods, which are a common natural food source for many wild boar populations, are practically absent. We hypothesised that the proportion of cultivated area and especially supplementary feeding, which is widely used in Estonia to lower the winter mortality of game species, play important roles in sustaining the local wild boar population. To determine the most important factors shaping the abundance of wild boar in a northern environment, we developed mixed models to account for variation in an index of wild boar abundance (AI) based on winter track counts. The abundance of supplementary feeding sites and mean January temperature were the most important factors determining wild boar winter abundance. We conclude that the current high local population density is sustained by intensive supplementary feeding, which has exceeded the limiting effect of harsh winters.     

Are badgers ‘Under The Weather’? Direct and indirect impacts of climate variation on European badger (Meles meles) population dynamics

Weather conditions, and how they in turn define and characterize regional climatic conditions, are a primary limit on global species diversity and distribution, and increasing variability in global and regional climates have significant implications for species and habitat conservation. A Capture–Mark–Recapture study revealed that badger (Meles meles) life history parameters interact in complicated ways with annual variability in the seasonality of temperature and rainfall, both in absolute and in phenological terms. A strong predictive relationship was observed between survival and both temperature and late‐summer rainfall. This link at the population dynamics level was related to individual body‐weight increases observed between summer and autumn. In addition, fecundity was correlated with spring rainfall and temperature. We investigated and confirmed that relationships were consistent with observed variation in the intensity of a parasitic infection. Finally, fecundity during any given year correlated with conditions in the preceding autumn. Badger survival also correlated with late winter weather conditions. This period is critical for badgers insofar as it coincides with their peak involvement in road traffic accidents (RTAs). RTA rate during this period was linked strongly to temperature, underlining the intricate ways in which a changing climate might interact with anthropogenic agents to influence species' population processes. Equinoctial conditions produced significant population driver effects. That is, while summers will always be relatively warm compared with winters, spring and autumn weather can be more variable and functionally delimit the ‘productive’ vs. nonproductive period of the year in terms of badger behavioural and physiological cycles. This study highlights how appropriately informed conservation strategies, mindful of trends in climatic conditions, will become ever‐more essential to ensure the survival of many species globally.     

Influence of body mass and environmental conditions on winter mortality risk of a northern ungulate: Evidence for a late‐winter survival bottleneck

1. A relationship between winter weather and survival of northern ungulates has long been established, yet the possible roles of biological (e.g., nutritional status) and environmental (e.g., weather) conditions make it important to determine which potential limiting factors are most influential.
2. Our objective was to examine the potential effects of individual (body mass and age) and extrinsic (winter severity and snowmelt conditions) factors on the magnitude and timing of mortality for adult (>2.5 years old) female white‐tailed deer (Odocoileus virginianus [Zimmerman, 1780]) during February–May in the Upper Peninsula of Michigan, USA.
3. One hundred and fifty deer were captured and monitored during 2009–2015 in two areas with varying snowfall. February–May survival ranged from 0.24 to 0.89 (mean = 0.69) across years. Mortality risk increased 1.9% with each unit increase in cumulative winter severity index, decreased 8.2% with each cumulative snow‐free day, and decreased 4.3% with each kg increase in body mass. Age and weekly snow depth did not influence weekly deer survival. Predation, primarily from coyote (Canis latrans [Say, 1823]) and wolves (Canis lupus [L., 1758]), accounted for 78% of known‐cause mortalities.
4. Our results suggest that cumulative winter severity, and possibly to a lesser degree deer condition entering winter, impacted deer winter survival. However, the timing of spring snowmelt appeared to be the most influential factor determining late‐winter mortality of deer in our study. This supports the hypothesis that nutrition and energetic demands from weather conditions are both important to northern ungulate winter ecology. Under this model, a delay of several weeks in the timing of spring snowmelt could exert a large influence on deer survival, resulting in a survival bottleneck.

     

Differential ecophysiological response of deciduous shrubs and a graminoid to long-term experimental snow reductions and additions in moist acidic tundra, Northern Alaska

Changes in winter precipitation that include both decreases and increases in winter snow are underway across the Arctic. In this study, we used a 14-year experiment that has increased and decreased winter snow in the moist acidic tussock tundra of northern Alaska to understand impacts of variation in winter snow depth on summer leaf-level ecophysiology of two deciduous shrubs and a graminoid species, including: instantaneous rates of leaf gas exchange, and δ¹³C, δ¹⁵N, and nitrogen (N) concentrations of Betula nana, Salix pulchra, and Eriophorum vaginatum. Leaf-level measurements were complemented by measurements of canopy leaf area index (LAI) and depth of thaw. Reductions in snow lowered summer leaf photosynthesis, conductance, and transpiration rates by up to 40 % compared to ambient and deep snow conditions for Eriophorum vaginatum, and reduced Salix pulchra conductance and transpiration by up to 49 %. In contrast, Betula nana exhibited no changes in leaf gas exchange in response to lower or deeper snow. Canopy LAI increased with added snow, while reduced winter snow resulted in lower growing season soil temperatures and reduced thaw depths. Our findings indicate that the spatial and temporal variability of future snow depth will have individualistic consequences for leaf-level C fixation and water flux by tundra species, and that these responses will be manifested over the longer term by changes in canopy traits, depth of thaw, soil C and N processes, and trace gas (CO₂ and H₂O) exchanges between the tundra and the atmosphere.     

Rainfall during parental care reduces reproductive and survival components of fitness in a passerine bird

Adverse weather conditions during parental care may have direct consequences for offspring production, but longer‐term effects on juvenile and parental survival are less well known. We used long‐term data on reproductive output, recruitment, and parental survival in northern wheatears (Oenanthe oenanthe) to investigate the effects of rainfall during parental care on fledging success, recruitment success (juvenile survival), and parental survival, and how these effects related to nestling age, breeding time, habitat quality, and parental nest visitation rates. While accounting for effects of temperature, fledging success was negatively related to rainfall (days > 10 mm) in the second half of the nestling period, with the magnitude of this effect being greater for breeding attempts early in the season. Recruitment success was, however, more sensitive to the number of rain days in the first half of the nestling period. Rainfall effects on parental survival differed between the sexes; males were more sensitive to rain during the nestling period than females. We demonstrate a probable mechanism driving the rainfall effects on reproductive output: Parental nest visitation rates decline with increasing amounts of daily rainfall, with this effect becoming stronger after consecutive rain days. Our study shows that rain during the nestling stage not only relates to fledging success but also has longer‐term effects on recruitment and subsequent parental survival. Thus, if we want to understand or predict population responses to future climate change, we need to consider the potential impacts of changing rainfall patterns in addition to temperature, and how these will affect target species' vital rates.     

Winter severity limits red fox populations in Eurasia

Aim  We investigated geographical variation in the density of the red fox in relation to climatic variables, habitat productivity and seasonality to identify those factors that were the best predictors of fox density.
Location  Published data on red fox abundance were collated from 69 locations over Europe and Asia.
Methods  Using generalized linear models and the information-theoretic approach, we analysed the contribution of climatic measures (winter and summer temperature, mean snow depth and duration), primary productivity and seasonality indices [based on the fraction of photosynthetically active radiation (FPAR) index] to account for variation in red fox density.
Results  Red fox density in winter ranged from 0.001–2.8 individuals km⁻²; the average density was 0.21 individuals km⁻². Variation in red fox density was best explained by the winter temperature and seasonality. Density decreased with declining winter and summer temperatures, increasing degree of seasonality and increasing duration of snow cover. There was no relationship with habitat productivity.
Main conclusions  Our results indicate that winter climatic conditions and seasonality, but not habitat productivity, may limit red fox density in Eurasia. One explanation for the limitation of the red fox population may be the fox's physiological capability to cope with abiotic conditions. Concurrently, the severity of winter may lead to reduced availability of the fox's prey. That, together with a shorter reproductive period may result in lower reproductive output as well as lower survival of adults and cubs.     

大兴安岭北坡黑嘴松鸡越冬期种群密度及夜栖地利用

为了更深入地了解黑嘴松鸡的种群密度及其夜栖地利用情况,以期为后续的黑嘴松鸡保护管理提供科学的理论参考,2017—2018年1—2月采用样线法、定点观察法、样方法、因子测量法、因子分析法、GPS定位等方法,对大兴安岭北坡越冬期黑嘴松鸡的种群密度及夜栖地特征进行了调查分析。分析结果表明:(1)大兴安岭北坡越冬期,黑嘴松鸡种群密度为(1.18—8.06)只/km~2,即每平方千米分布有黑嘴松鸡1—8只;(2)黑嘴松鸡夜栖卧迹长为(52.64±9.28) cm、宽为(26.55±6.91) cm、高为(17.11±3.78) cm;(3)黑嘴松鸡夜栖地利用包括2个尺度3个选择,即大生境尺度内夜栖生境类型选择和小生境尺度内夜栖区选择、夜栖微生境选择;(4)夜栖生境类型对以兴安落叶松为优势树种的针阔混交林具有绝对的选择性(100%);夜栖区对林缘雪地和林中乔木树下的偏好利用较高(75.00%);夜栖微生境选择通过隐蔽因子、应急逃逸因子、温度因子来判定,隐蔽因子包括乔木密度和干扰区距离,选择具有高密度乔木的、远离人为干扰区(约为4.5 km)的区域;应急逃逸因子包括海拔、卧迹头端开阔度、乔木距离,选择高海拔的、卧迹头端具有开阔度的、贴近乔木(小于1 m)的位置;温度因子包括卧迹雪深、卧迹头端方位角,选择保温效果显著的、适合体尺指标的背风点(东南出口)。     

Snow cover manipulations alter survival of early life stages of cold‐temperate tree species

Projections of future climate suggest increases in global temperatures that are especially pronounced in winter in cold‐temperate regions. Thermal insulation provided by snow cover to litter, soil, and overwintering plants will likely be affected by changing winter temperatures and might influence future species composition and ranges. We investigated effects of changing snow cover on seed germination and sapling survival of several cold‐temperate tree species using a snow manipulation approach. Post‐winter seed germination increased or decreased with increasing snow cover, depending on species; decreased seed germination was found in species that characteristically disperse seed in summer or fall months prior to snowfall. Post‐winter sapling survival increased with increasing snow cover for all species, though some species benefitted more from increased snow cover than others. Sapling mortality was associated with root exposure, suggesting the possibility that soil frost heaving could be an important mechanism for observed effects. Our results suggest that altered snow regimes may cause re‐assembly of current species habitat relationships and may drive changes in species’ biogeographic range. However, local snow regimes also vary with associated vegetation cover and topography, suggesting that species distribution patterns may be strongly influenced by spatial heterogeneity in snow regimes and complicating future projections.     

Winter survival of age-0 smallmouth bass, <Emphasis Type="Italic">Micropterus dolomieu</Emphasis>, in north eastern lakes

We examined the winter survival of age-0 smallmouth bass,Micropterus dolomieu, in lakes at their northern limit of distribution in New Brunswick, Canada. Pre- and post-winter collections over a 3 year period suggested the smallest individuals, <50 mm total length, died during winter under ice. Experiments with wild, age-0 smallmouth bass held in lakes demonstrated a size-dependent survival where smaller individuals had greater survival with an increasing temperature of exposure, but the largest individuals had reduced survival at warmer temperatures. Survivors lost 22–54% of pre-winter energy reserves measured as ash-free dry weight, which was similar to wild individuals captured in spring. Body size at the onset of winter affects survival, but it also appears that temperature interacting with a suite of environmental and biological factors affect changes in energy use and therefore survival of age-0 smallmouth bass under ice in winter.