Lack of compensatory body growth in a high performance moose Alces alces population

Considerable work has been done on disentangling important factors determining early development in body size, yet our knowledge of the extent to which animals living under varying conditions can achieve catch-up growth for a bad start in life is limited. Here, we investigated how body mass at the age of 8 months influenced adult body mass in a moose Alces alces population living under excellent environmental conditions on the island of Vega in northern Norway. We also investigated if mother age and birth date effects on calf body mass persisted until adulthood. We show that neither males nor females were able to show compensatory growth before they reached adulthood, and that part of the variation in adult body mass may have been due to variation in mother age and date of birth. The pattern observed in males can be related to their growth strategy in relation to reproduction, while such results were not expected in females where size-dependent start of reproduction is likely to interact with body growth. We suggest that the good environmental conditions experienced on Vega led to females having small somatic costs of an early start of reproduction or that larger females were able to acquire more resources for growth than their smaller conspecifics. In both cases, females that postpone their first reproduction may not be able to achieve catch-up growth for their lower early body mass compared to females that start reproduction at an early age. Our results concur with previous studies indicating that compensatory growth is weak in moose, increasing the likelihood that variation in life history characters are also transferred between generations.     

Life history patterns in female moose (Alces alces): the relationship between age,body size,fecundity and environmental conditions

I examined the relationship between age, body size and fecundity in 833 female moose (Alces alces) from 14 populations in Sweden sampled during 1989–1992. Data on population density, food availability and climatic conditions were also collected for each population. Age and body mass were both significantly positively related to fecundity, measured as ovulation rate, among female moose. The relationship between the probability of ovulation and body mass was dependent on age with (1) a higher body mass needed in younger females for attaining a given fecundity, and (2) body mass having a stronger effect on fecundity in yearling (1.5 year) than in older (2.5 year) females. Thus, a 40 kg increase in yearling body mass resulted in a 42% increase in the probability of ovulation as compared to a 6% increase in older females. The lower reproductive effort per unit body mass, and the relatively stronger association between fecundity and body mass in young female moose compared to older ones, is likely to primarily represent a mechanism that trades off early maturation against further growth, indicating a higher cost of reproduction in young animals. In addition to age and body mass, population identity explained a significant amount of the individual variation in fecundity, showing that the relationship between body mass and fecundity was variable among populations. This variation was in turn related to the environment, in terms of climatic conditions forcing female moose living in relatively harsh/more seasonal climatic conditions to attain a 22% higher body mass to achive the same probability of multiple ovulation (twinning) as females living in climatically milder/less seasonal environments. The results suggests that the lower fecundity per unit body mass in female moose living in climatically harsh/more seasonal environments may be an adaptive response to lower rates of juvenile survival, compared to females experiencing relatively milder/less seasonal climatic conditions.     

Dynamics of a harvested moose population in a variable environment

1. Population size, calves per female, female mean age and adult sex ratio of a moose ( Alces alces ) population in Vefsn, northern Norway were reconstructed from 1967 to 1993 using cohort analysis and catch-at-age data from 96% (6752) of all individuals harvested.
2. The dynamics of the population were influenced mainly by density-dependent harvesting, stochastic variation in climate and intrinsic variation in the age-structure of the female segment of the population.
3. A time delay in the assignment of hunting permits in relation to population size increased fluctuations in population size.
4. Selective harvesting of calves and yearlings increased the mean age of adult females in the population, and, because fecundity in moose is strongly age-specific, the number of calves per female concordantly increased. However, after years with high recruitment, the adult mean age decreased as large cohorts entered the adult age-groups. This age-structure effect generated cycles in the rate of recruitment to the population and fluctuations introduced time-lags in the population dynamics.
5. An inverse relationship between recruitment rate and population density, mediated by a density-dependent decrease in female body condition, could potentially have constituted a regulatory mechanism in the dynamics of the population, but this effect was counteracted by a density-dependent increase in the mean age of adult females.
6. Stochastic variation in winter snow depth and summer temperature had delayed effects on recruitment rate and in turn population growth rate, apparently through effects on female body condition before conception.     

Environmental phenology and geographical gradients in moose body mass

Intraspecific body mass in ungulates has often been shown to increase with latitude. The biological basis for such latitudinal gradients is, however, poorly known. Here we examined whether satellite-derived indices of environmental phenology, based on the normalised difference vegetation index (NDVI), as well as variables derived from meteorological stations, altitude, and population density, can explain latitudinal gradients and regional variation in body mass of Norwegian moose. The best model gave a considerably better fit than latitude alone, and included all explanatory environmental variables. Accordingly, heavy moose were found in areas with short and intense summers that were followed by long, cold winters, at low altitude relative to the tree-limit, and with low population density relative to the available plant biomass. This relationship was stronger for yearlings than for calves, except for the effect of population density. This indicates that differences in the characteristics of the vegetation quality and environmental phenology, as well as winter harshness and population density, are important factors that shape both the latitudinal and other geographical gradients in moose body mass.     

Mobility of moose—comparing the effects of wolf predation risk,reproductive status,and seasonality

In a predator–prey system, prey species may adapt to the presence of predators with behavioral changes such as increased vigilance, shifting habitats, or changes in their mobility. In North America, moose (Alces alces) have shown behavioral adaptations to presence of predators, but such antipredator behavioral responses have not yet been found in Scandinavian moose in response to the recolonization of wolves (Canis lupus). We studied travel speed and direction of movement of GPS‐collared female moose (n = 26) in relation to spatiotemporal differences in wolf predation risk, reproductive status, and time of year. Travel speed was highest during the calving (May–July) and postcalving (August–October) seasons and was lower for females with calves than females without calves. Similarly, time of year and reproductive status affected the direction of movement, as more concentrated movement was observed for females with calves at heel, during the calving season. We did not find support for that wolf predation risk was an important factor affecting moose travel speed or direction of movement. Likely causal factors for the weak effect of wolf predation risk on mobility of moose include high moose‐to‐wolf ratio and intensive hunter harvest of the moose population during the past century.     

Population characteristics predict responses in moose body mass to temporal variation in the environment

1. A general problem in population ecology is to predict under which conditions stochastic variation in the environment has the stronger effect on ecological processes. By analysing temporal variation in a fitness-related trait, body mass, in 21 Norwegian moose Alces alces (L.) populations, we examined whether the influence of temporal variation in different environmental variables were related to different parameters that were assumed to reflect important characteristics of the fundamental niche space of the moose. 2. Body mass during autumn was positively related to early access to fresh vegetation in spring, and to variables reflecting slow phenological development (low June temperature, a long spring with a slow plant progression during spring). In contrast, variables related to food quantity and winter conditions had only a minor influence on temporal variation in body mass. 3. The magnitude of the effects of environmental variation on body mass was larger in populations with small mean body mass or living at higher densities than in populations with large-sized individuals or living at lower densities. 4. These results indicate that the strongest influence of environmental stochasticity on moose body mass occurs towards the borders of the fundamental niche space, and suggests that populations living under good environmental conditions are partly buffered against fluctuations in environmental conditions.     

Winter climate, age, and population density affect the timing of conception in female moose (Alces alces)

Phenological events such as conception or parturition dates may have profound impact on several key life-history traits of ungulates at the individual as well as the population level. However, relatively little is known about the causes of variation in the timing of reproduction. Based on a 17-year survey of reproductive tracts, we investigated the effect of climate, population density, and age on the conception date of female moose (Alces alces) harvested in Estonia. Ninety-five percent of studied moose cows were conceived within a period of 9 weeks (29 August–30 October), while more than 45 % of all moose cows were conceived from 19 September to 2 October. Conception date was negatively related to population density and nonlinearly to the regional measure of winter climate reflecting the maximal extent of ice on the Baltic Sea (MIE) in the previous winter. High air temperatures during rut (in September) delayed the conception date. The timing of conception also depended on female age. Yearlings conceived significantly later as compared to females of all other age groups. Our findings corroborate the importance of density-dependent as well density-independent processes on the timing of conception of this ungulate. We also propose that the effect of population density on conception date may be mediated by increasing ecological carrying capacity concurrent with increasing population abundance.     

Effects of inbreeding on fitness‐related traits in a small isolated moose population

Inbreeding can affect fitness‐related traits at different life history stages and may interact with environmental variation to induce even larger effects. We used genetic parentage assignment based on 22 microsatellite loci to determine a 25 year long pedigree for a newly established island population of moose with 20–40 reproducing individuals annually. We used the pedigree to calculate individual inbreeding coefficients and examined for effects of individual inbreeding (f) and heterozygosity on fitness‐related traits. We found negative effects of f on birth date, calf body mass and twinning rate. The relationship between f and calf body mass and twinning rate were found to be separate but weaker after accounting for birth date. We found no support for an inbreeding effect on the age‐specific lifetime reproductive success of females. The influence of f on birth date was related to climatic conditions during the spring prior to birth, indicating that calves with a low f were born earlier after a cold spring than calves with high f. In years with a warm spring, calf f did not affect birth date. The results suggest that severe inbreeding in moose has both indirect effects on fitness through delayed birth and lower juvenile body mass, as well as separate direct effects, as there still was a significant relationship between f and twinning rate after accounting for birth date and body mass as calf. Consequently, severe inbreeding as found in the study population may have consequences for population growth and extinction risk.     

Patterns of hunting mortality in Norwegian moose (Alces alces) populations

We used a simple life table approach to examine the age-specific patterns of harvest mortality in eight Norwegian moose populations during the last 15 years and tried to determine if the observed patterns were caused by hunter selectivity. The general opinion among local managers is that hunters prefer to shoot female moose not in company with calves to keep a high number of reproductive females in the population (and because of the emotional stress involved in leaving the calf/calves without a mother), and relatively large males because of the higher return with respect to meat and trophy. In support of the former view, we found the harvest mortality of adult females to be higher among pre-prime (1–3 years old) than prime-aged age classes (4–7 years old). This is probably because prime-aged females are more fecund and, therefore, more likely to be in company with one or two calves during the hunting season. As the season progressed, however, the selection pressure on barren females decreased, probably due to more productive females becoming ‘legal’ prey as their calf/calves were harvested. In males, we did not find any evidence of strong age-specific hunter selectivity, despite strong age-dependent variation in body mass and antler size. We suggest that this was due to the current strongly female-biased sex ratio in most Norwegian moose populations, which leaves the hunters with few opportunities to be selective within a relatively short and intensive hunting season. The management implications of these findings and to what extent the results are likely to affect the future evolution of life histories in Norwegian moose populations are discussed.Electronic Supplementary Material Supplementary material is available for this article at and accessible for authorised users.     

Effects of willow nutrition and morphology on calving success of moose

Across much of North America, populations of moose (Alces alces) are declining because of disease, predation, climate change, and anthropogenic-driven habitat loss. Contrary to this trend, populations of moose in Colorado, USA, have continued to grow. Studying successful (i.e., persistent or growing) populations of moose can facilitate continued conservation by identifying habitat features critical to persistence of moose. We hypothesized that moose using habitat with higher quality willow (Salix spp.) would have a higher probability of having a calf-at-heel (i.e., calving success). We evaluated moose calving success using repeated ground observations of collared individuals with calves in an occupancy model framework to account for detection probability. We then evaluated the impact of willow habitat quality and nutrition on moose calving success by studying 2 spatially segregated populations of moose in Colorado. Last, we evaluated correlations between willow characteristics (browse intensity, height, cover, leaf length, and species) and willow nutrition (dry matter digestibility [DMD]) to assess the utility of using those characteristics to assess willow nutrition. We found willow height and cover had a high probability of being positively associated with higher individual-level calving success. Willow DMD, browse intensity, and leaf length were not predictive of individual moose calving success; however, the site with higher mean DMD consistently had higher mean estimates of calving success for the same year. Our results suggest surveying DMD is likely not a useful metric for assessing differences in calving success of individual moose but may be of use at population levels. Further, the assessment of willow morphology and density may be used to identify areas that support higher levels of moose calving success.     

Range-body mass interactions of a northern ungulate – a test of hypothesis

Summer diet, summer temperature, length of the growth season and animal density appeared to best explain annual and regional differences in calf and yearling body mass in moose from southeastern Norway. In general animals inhabiting steep, alpine landscapes had less body mass than animals using flat, low-altitude habitats. Autumn body mass of calves and yearlings decreased with increasing snow depth during the preceding winter and spring. However, calf body mass was more influenced by the summer range and less by the winter range than was body mass of yearlings. There was no indication that the effect of snow depth on autumn body mass was greater in moose living on poor than on good summer ranges. Body mass decreased with increasing competition for summer forage, while the winter range mainly had an density-independent effect. Habitat quality, expressed as regression lines between calf and yearling body mass and animal density (hunting yield), differed between regions. On ranges of medium and high altitude where birch (Betula spp.) rowan (Sorbus aucuparia) and bilberry (Vaccinium myrtillus) dominated moose summer diet, body mass decreased at a rapid rate with increasing animal density. Body mass decreased at a slower rate at low-altitude ranges and at high-altitude ranges where willow (Salix spp.) and forbs dominated the diet. Body mass of lactating cows decreased with increasing animal density, but animal density did not affect body mass of non-lactating cows. There was no indication that the decrease in autumn body mass with increasing moose density over the last 25 years has caused a decrease in animal condition (ability to survive the winter). The results are discussed in relation to the effect of summer and winter range on population regulation in moose. It is concluded that a density-dependent effect is apparent on the summer range even at low and intermediate population densities. On the winter range, on the other hand, density-dependence is likely to occur only at high levels of population density. Received: 4 February 1997 / Accepted: 1 February 1999     

Geographical and latitudinal variation in growth patterns and adult body size of Swedish moose (Alces alces)

We examined the geographical pattern in growth and adult body size among 14 populations of Swedish moose (Alces alces) using data from 4,294 moose (1.5 years old) killed during the hunting season in 1989–1992. In both sexes, adult body mass was significantly positively correlated with latitude. Moose in northern populations had a 15–20% larger adult body mass than moose in the south. Juvenile body mass was correlated with neither latitude nor adult body mass. Thus, variation in time (years) and rate of body growth after the juvenile stage were responsible for most of the variation in adult body mass among populations. Moose in northern populations grew for approximately 2 more years of life than southern moose. In contrast to adult body mass, skeletal size (measured as jawbone length) was not correlated with latitude, suggesting that variation in adult body mass was primarily due to differences in fat reserves. Discrimination between population characteristics, such as moose density, climate, and the amount of browse available to moose, showed climatic harshness to be the most important variable explaining geographical variation in body mass among populations. The results support the notion that in mammals body size increases with latitude in accordance with Bergmann's rule. We conclude that (1) variation in patterns of growth after the juvenile stage is the main cause of the latitudinal trend in adult body size in moose, and (2) climatic conditions are a more important factor than population density and availability of food in explaining geographical variation in growth patterns and adult body mass between populations of Swedish moose.     

Sex ratio variation in harvested moose (<Emphasis Type="Italic">Alces alces</Emphasis>) calves: does it reflect population calf sex ratio or selective hunting?

During the last 30 years, the proportion of males in the calf harvest of moose (Alces alces) in Norway has decreased, indicating a decline in proportions of males recruited to the autumn populations. At the same time, the percentages of exclusive calf hunting permits and of calves shot have increased. The change in calf sex ratio may thus simply be the result of hunter preferences for slightly larger (6.2% higher body mass) male calves combined with fewer opportunities for selective hunting due to increasing hunting quotas of calves. We examined this hypothesis by analyzing the variation in sex, number of siblings, carcass mass, date, and location of kill of 16,330 moose calves harvested during 1970–2004. In the presence of hunting selection for larger calves, we predicted larger proportions of male calves to be harvested in populations with large sexual size dimorphism among calves. Similarly, we expected more males to be harvested from twin than single litters because hunters then can more easily compare twins and select the larger calf, which is more often a male. Increasing proportions of single female calves were also expected to occur in the daily harvest as the accumulated number of harvested calves increased and the proportion of calves left in the population decreased. We found no positive relationship between the proportion of male calves and the level of sexual size dimorphism, no clear difference in sex ratio between harvested single and twin calves, and no increase in the proportion of single female calves as the accumulated number of calves in the harvest increased. This suggests that the spatiotemporal variation in the harvest calf sex ratio in Norway most likely reflects differences in population calf sex ratios prior to the hunting season and not varying degrees of hunting selectivity.     

The influence of prey consumption and demographic stochasticity on population growth rate of Isle Royale wolves Canis lupus

The relationship between the rates of prey capture and predator population growth is a fundamental aspect of predation, yet it is rarely measured for vertebrate predators. For the isolated wolf population on Isle Royale, annual variation in kill rate explains 22% of the variation in wolf population growth rate. From the slope of this relationship, we estimate that the production efficiency (ratio of production to respiration) of wolves is between 0.5% and 1.5%. More generally, we assess the relative extent to which wolf population growth rate is affected by density dependence, prey availability (moose, Alces alces ), winter weather, and demographic stochasticity. Prey availability explains the most variation in wolf growth rate (42%), but this is only recognized after accounting for the influence of a disease-induced population crash and age structure of the prey population (i.e. number of vulnerable moose, >9 years of age). Demographic stochasticity accounts for approximately 30% of the variation in wolf growth rate. This recognition is important, but not surprising, given that the average population size of Isle Royale wolves is 22. Previous work indicates that the effect of winter climate, as mediated through prey vulnerability and kill rates, is substantial. This work indicates that the direct effect of winter climate is weak, and explains only about 4% of the variation in wolf growth rate (P=0.10).     

Environmental variation and moose Alces alces density as determinants of spatio-temporal heterogeneity in browsing

Understanding temporal variation in habitat selection and browsing intensity by large herbivores is fundamental because of their large impact on the ecosystems. I studied the annual variation in winter browsing pressure on young trees and habitat selection by moose Alces alces over a ten year period. Specifically, the relationships between browsing pressure on Scots pine Pinus sylvestris and two birch species ( Betula ssp.) and three explanatory variables – 1) availability of forage, 2) moose density (estimated by pellet group counts) and 3) snow cover was studied. At a larger spatial scale (forest stand level) the relationship between moose habitat selection between three different habitat types (forest <30 yr, forest>30 yr and mire) and two explanatory variables, 1) snow condition and 2) moose density, were studied. Browsing pressure on Scots pine, the dominating food plant, was related to forage availability, moose density and snow condition. No significant relationships between any of the three explanatory variables and browsing pressure on the two birch species were found. Moose selection for certain habitats varied between years and was affected by number of days with >0.10 m of snow.
Habitat selection was not significantly related to moose density and the relationship between overall moose density and habitat specific moose densities was proportional within the studied density range. These findings have implications for understanding varying browsing patterns – and will affect both the ability to predict herbivores' effect on the forest ecosystem. A snow dependent browsing pattern also indicates that one can expect a long term decrease in browsing pressure on the tree and shrub layer as a consequence of the ongoing large-scale climate change.     

Long‐lived and heavier females give birth earlier in roe deer

In seasonal environments, parturition of most vertebrates generally occurs within a short time‐window each year. This synchrony is generally interpreted as being adaptive, as early born young survive better over the critical season than late born young. Among large herbivores, the factors involved in driving among‐ and within‐individual variation in parturition date are poorly understood. We explored this question by analyzing the relative importance of attributes linked to female quality (longevity, median adult body mass and cohort), time‐dependent attributes linked to female condition (reproductive success the previous year, relative annual body mass and offspring cohort (year)), and age in shaping observed variation in parturition date of roe deer. A measure of quality combining the effects of female longevity and median adult body mass accounted for 11% of the observed among‐individual variation in parturition date. Females of 2 yr old give birth 5 d later than older females. Our study demonstrates that high quality (heavy and long‐lived) females give birth earlier than low quality females. Temporally variable attributes linked to female condition, such as reproductive success in the previous year and relative annual body mass, had no detectable influence on parturition date. We conclude that parturition date, a crucial determinant of reproductive success, is shaped by attributes linked to female quality rather than by time‐dependent attributes linked to female condition in income breeders (individuals that rely on current resource intake rather than on accumulated body reserves to offset the increased energy requirements due to reproduction) such as roe deer.     

麋鹿鹿角脱落、群主更替、产仔的年节律及其环境影响因子

本文在2014—2016年三个冬季(12月—翌年2月)收集了北京南海子麋鹿苑半散放麋鹿自然脱落的角,并观察和记录了2015—2017年发情期(5—9月)群主更替和2016—2018年产仔期(3—7月)麋鹿幼仔出生情况,结合2014—2018年年平均气温、季平均气温、月平均气温、年降雨量、雨季开始时间、种群密度等环境因子,对鹿角脱落、群主更替、产仔等繁殖特征的年节律及其环境影响因子进行了研究。结果表明：1)麋鹿鹿角脱落、群主更替、产仔的年节律均存在年际差异。2)鹿角脱落时间为12月开始,1月下旬或2月上旬结束。3)发情期为5月下旬或6月上旬开始,9月上旬结束;2015—2017年发情期时间有延长的趋势。4)产仔期为3月中旬或4月中旬开始,5月下旬或7月下旬结束。5)麋鹿鹿角脱落、群主更替、产仔的年节律存在明显的同步关系,其中鹿角脱落开始时间、鹿角脱落高峰期、鹿角脱落结束时间、第一次发情期开始时间、群主更替高峰期、产仔期开始时间、产仔高峰期、产仔期结束时间与前一年度比较均出现同步提前的现象。6)鹿角脱落年节律存在随着12月平均气温升高而提前的现象;产仔期开始时间和产仔高峰期存在随着前一年9月平均气温的升高而提前的现象。7)鹿角脱落年节律表现出随着年降雨量的增多而提前的现象;第一次发情期开始时间、群主更替高峰期的年节律表现出随着前一年度年降雨量的增多而提前的现象。8)麋鹿鹿角脱落、群主更替、产仔的年节律均不存在随着种群密度升高或降低而提前或延迟的现象。麋鹿繁殖特征的年节律是一个复杂的过程,受气候、营养、种群密度、纬度等环境因子的影响。     

Behavioural Responses to Thermal Conditions Affect Seasonal Mass Change in a Heat-Sensitive Northern Ungulate

Background

Empirical tests that link temperature-mediated changes in behaviour (activity and resource selection) to individual fitness or condition are currently lacking for endotherms yet may be critical to understanding the effect of climate change on population dynamics. Moose (Alces alces) are thought to suffer from heat stress in all seasons so provide a good biological model to test whether exposure to non-optimal ambient temperatures influence seasonal changes in body mass. Seasonal mass change is an important fitness correlate of large herbivores and affects reproductive success of female moose.

Methodology/Principal Findings

Using GPS-collared adult female moose from two populations in southern Norway we quantified individual differences in seasonal activity budget and resource selection patterns as a function of seasonal temperatures thought to induce heat stress in moose. Individual body mass was recorded in early and late winter, and autumn to calculate seasonal mass changes (n = 52 over winter, n = 47 over summer). We found large individual differences in temperature-dependent resource selection patterns as well as within and between season variability in thermoregulatory strategies. As expected, individuals using an optimal strategy, selecting young successional forest (foraging habitat) at low ambient temperatures and mature coniferous forest (thermal shelter) during thermally stressful conditions, lost less mass in winter and gained more mass in summer.

Conclusions/Significance

This study provides evidence that behavioural responses to temperature have important consequences for seasonal mass change in moose living in the south of their distribution in Norway, and may be a contributing factor to recently observed declines in moose demographic performance. Although the mechanisms that underlie the observed temperature mediated habitat-fitness relationship remain to be tested, physiological state and individual variation in thermal tolerance are likely contributory factors. Climate-related effects on animal behaviour, and subsequently fitness, are expected to intensify as global warming continues.     

Modeling female brown bear kill rates on moose calves using global positioning satellite data

The recent development in Global Positioning System (GPS) techniques has started a new era in predation studies. Estimates of kill rates based on animal movements and GPS relocation clusters have proven to be valid in several obligatory carnivores. The main focus has been to obtain accurate mean predation estimates for the management of wildlife populations. We present a model to estimate individual kill rates of moose calves by adult female brown bears in Sweden, based on spatiotemporal clustering of 30,889 bear GPS relocations and 71 moose calves verified killed during 714 field investigations in 2004–2006. In this virtually single-predator single large prey system, the omnivorous brown bear is an efficient predator on moose calves up to 4 weeks of age. The top model set only included models with cluster radii of 30 m or 50 m, indicating very high kill-site fidelity. The best model included a cluster radius of 30 m and number of periods of bear activity at the kill site as a single covariate. The mean estimated individual kill rate of 7.6 ± 0.71 (n = 18, ± SE) moose calves per calving season is comparable to the estimate of 6.8 from a previous study of radio-tracked moose in our study area, though at a lower moose/bear ratio. The mean annual kill rates varied from 6.1 to 9.4 calves per bear. The estimated individual kill rates ranged from 2 to 15 calves per season, indicating a large individual variation in hunting skills and possibly effort. Predation and livestock depredation represent a core conflict between humans and carnivores in rural Scandinavia. Accurate predation estimates represent an important step in quantifying costs of carnivores and reducing human–carnivore conflicts. Our technique may be applied in the exploration of predation mechanisms and predator–prey interactions, and contribute to the old and global debate of problem individuals in livestock depredation. © 2012 The Wildlife Society.     

Body mass and winter mortality in red deer calves: disentangling sex and climate effects

Understanding population dynamics of large mammals requires studies of variation in the age and sex–specific demographic parameters over time and the factors causing this variation. Here, we have focused on the variation in body mass of 8-10–month old red deer calves, in relation to climate and sex over a 20-yr period (1977–1997). We investigated the relationship between body mass and over–winter mortality during 1985 and 1986 and thereby, the phenotypic selection on body mass. We found a high variability from year to year in calf body mass. Males were consistently heavier than females. No interaction between sex and year was detected. The body mass of individuals from the same cohort shot during the annual hunting season and snow depth in January each explained ca 20% of the variability in calf body mass. Body mass loss during winter did not differ between sexes, but increased with body mass and varied from year to year. The probability of surviving was strongly related to body mass in each sex. For a given body mass relative to the sex–specific mean, males had a lower probability of survival than females. Hence, males had to be 1 kg larger than their mean in order to achieve the same survival as average-sized females. Our results suggested a directional phenotypic selection on body mass that led to an increasing body mass dimorphism in calves. The strength of this selection and the sex difference in the shape of the selection curve may depend, however, on the severity of winter and on sexual dimorphism in body mass at the beginning of winter.