Erlend B. Nilsen

Is hunting mortality additive or compensatory to natural mortality? Effects of experimental harvest on the survival and cause‐specific mortality of willow ptarmigan

1. The effects of harvest on the annual and seasonal survival of willow ptarmigan Lagopus lagopus L. were tested in a large-scale harvest experiment. Management units were randomly assigned to one of three experimental treatments: 0%, 15% or 30% harvest. Seasonal quotas were based on the experimental treatment and estimates of bird density before the hunting season. Survival rates and hazard functions for radio-marked ptarmigan were then estimated under the competing risks of harvest and natural mortality. 2. The partially compensatory mortality hypothesis was supported: annual survival of ptarmigan was 0·54 ± 0·08 SE under 0% harvest, 0·47 ± 0·06 under 15% harvest, and was reduced to 0·30 ± 0·05 under 30% harvest. Harvest mortality increased linearly from 0·08 ± 0·05, 0·27 ± 0·05 and 0·42 ± 0·06 from 0% to 30% harvest, whereas natural mortality was 0·38 ± 0·08, 0·25 ± 0·05 and 0·28 ± 0·06 under the same treatments. 3. Realized risk of harvest mortality was 0·08-0·12 points higher than our set harvest treatments of 0-30% because birds were exposed to risk if they moved out of protected areas. The superadditive hypothesis was supported because birds in the 30% harvest treatment had higher natural mortality during winter after the hunting season. 4. Natural mortality was mainly because of raptor predation, with two seasonal peaks in fall and spring. Natural and harvest mortality coincided during early autumn with little potential for compensation during winter months. Peak risk of harvest mortality was 5× higher than natural mortality. Low natural mortality during winter suggests that most late season harvest would be additive mortality. 5. Environmental correlates of natural mortality of ptarmigan included seasonal changes in snow cover, onset of juvenile dispersal, and periods of territorial activity. Natural mortality of ptarmigan was highest during autumn movements and nesting by gyrfalcons Falco rusticolus L. Mortality was low when gyrfalcons had departed for coastal wintering sites, and during summer when ptarmigan were attending nests and broods. 6. Our experimental results have important implications for harvest management of upland gamebirds. Seasonal quotas based on proportional harvest were effective and should be set at ≤ 15% of August populations for regional management plans. Under threshold harvest of a reproductive surplus, 15% harvest would be sustainable at productivity rates ≥ 2·5 young per pair. Impacts of winter harvest could be minimized by closing the hunting season in early November or by reducing late season quotas.

Can intra-specific variation in carnivore home-range size be explained using remote-sensing estimates of environmental productivity?

ABSTRACT Carnivore home-range sizes vary profoundly between populations within a species. One commonly cited reason for this is variation in prey population density and environmental productivity. However, obtaining reliable measures of prey density in the field is both time and effort consuming. Therefore, a methodology that enabled scientists and managers to extrapolate home-range sizes across areas would be a valuable tool. So far, the potentials of different remote-sensing indices to represent environmental productivity have been poorly evaluated in this context. In this study, we have evaluated the utility of a readily available remote-sensing index, the Fraction of Photosynthetically Active Radiation absorbed by vegetation canopies (FPAR), to explain interpopulation variation in home-range size for 12 carnivore species. In multiple regression models, evaluated by the Bayesian Information Criterion (BIC), we found that the FPAR index added predictive power to the models for eight of the species. The explanatory power varied between 16% and 71% for the different species. We suggest that using remote-sensing indices such as FPAR to predict area specific home-range sizes for carnivores could potentially be a powerful tool, but that the methodology needs to be further developed in order to add more explanatory power for some species.

Can minimum convex polygon home ranges be used to draw biologically meaningful conclusions

Many conclusions about mammalian ranging behaviour have been drawn based on minimum convex polygon (MCP) estimates of home range size, although several studies have revealed its unpredictable nature compared to that of the kernel density estimator. We investigated to what extent the choice of home range estimator affected the biological interpretation in comparative studies. We found no discrepancy when the question asked covered a wide range of taxa, as real and very large differences in range size were likely to have masked smaller differences due to the choice of home range estimator. However, when the question asked concerned within-species characteristics, the choice of home range estimator explained as much of the variation in range size as did the ecological variable in question. The implications for macro-ecological and intraspecific studies are discussed.

Climate, season, and social status modulate the functional response of an efficient stalking predator: the Eurasian lynx

1. Predation plays a major role in shaping the structure and dynamics of ecological communities, and the functional response of a predator is of crucial importance to the dynamics of any predator-prey system by linking the trophic levels. For large mammals, there is a dearth of field studies documenting functional responses, and observations at low prey density are particularly scarce. Furthermore, there is a lack of understanding about how variables such as season, social status and climate modulate the functional response curves. 2. We analysed kill rate data collected over a 10-year period based on radio-marked lynx (Lynx lynx) mainly preying on roe deer (Capreolus capreolus) along a steep prey density gradient in south-eastern Norway. 3. The asymptotic kill rate was reached at a very low prey density for both solitary individuals and family groups (i.e. females with their dependent kittens), indicative of an efficient predator. This highlights the importance of understanding the interplay between predator and prey at low prey densities. 4. A purely prey-dependent functional response was a poor descriptor of the data, as the curve was strongly modulated by season and differences between lynx of different social status. In addition, there was a clear effect of abiotic climatic factors (indexed by the North Atlantic Oscillation) on observed kill rates in the more snow-rich portion of our study area. 5. Our analysis suggests that simple functional response curves might be poor descriptors of predator consumption rates in complex natural system, and that auxiliary factors are likely to induce complexity into any predator-prey systems that would not be captured by simple deterministic approaches.

Wolf reintroduction to Scotland: public attitudes and consequences for red deer management

Reintroductions are important tools for the conservation of individual species, but recently more attention has been paid to the restoration of ecosystem function, and to the importance of carrying out a full risk assessment prior to any reintroduction programme. In much of the Highlands of Scotland, wolves (Canis lupus) were eradicated by 1769, but there are currently proposals for them to be reintroduced. Their main wild prey if reintroduced would be red deer (Cervus elaphus). Red deer are themselves a contentious component of the Scottish landscape. They support a trophy hunting industry but are thought to be close to carrying capacity, and are believed to have a considerable economic and ecological impact. High deer densities hamper attempts to reforest, reduce bird densities and compete with livestock for grazing. Here, we examine the probable consequences for the red deer population of reintroducing wolves into the Scottish Highlands using a structured Markov predator–prey model. Our simulations suggest that reintroducing wolves is likely to generate conservation benefits by lowering deer densities. It would also free deer estates from the financial burden of costly hind culls, which are required in order to achieve the Deer Commission for Scotlands target deer densities. However, a reintroduced wolf population would also carry costs, particularly through increased livestock mortality. We investigated perceptions of the costs and benefits of wolf reintroductions among rural and urban communities in Scotland and found that the public are generally positive to the idea. Farmers hold more negative attitudes, but far less negative than the organizations that represent them.

Predicting the potential demographic impact of predators on their prey: a comparative analysis of two carnivore–ungulate systems in Scandinavia

1. Understanding the role of predation in shaping the dynamics of animal communities is a fundamental issue in ecological research. Nevertheless, the complex nature of predator–prey interactions often prevents researchers from modelling them explicitly. 2. By using periodic Leslie–Usher matrices and a simulation approach together with parameters obtained from long-term field projects, we reconstructed the underlying mechanisms of predator–prey demographic interactions and compared the dynamics of the roe deer–red fox–Eurasian lynx–human harvest system with those of the moose–brown bear–gray wolf–human harvest system in the boreal forest ecosystem of the southern Scandinavian Peninsula. 3. The functional relationship of both roe deer and moose λ to changes in predation rates from the four predators was remarkably different. Lynx had the strongest impact among the four predators, whereas predation rates by wolves, red foxes, or brown bears generated minor variations in prey population λ. Elasticity values of lynx, wolf, fox and bear predation rates were −0·157, −0·056, −0·031 and −0·006, respectively, but varied with both predator and prey densities. 4. Differences in predation impact were only partially related to differences in kill or predation rates, but were rather a result of different distribution of predation events among prey age classes. Therefore, the age composition of killed individuals emerged as the main underlying factor determining the overall per capita impact of predation. 5. Our results confirm the complex nature of predator–prey interactions in large terrestrial mammals, by showing that different carnivores preying on the same prey species can exert a dramatically different demographic impact, even in the same ecological context, as a direct consequence of their predation patterns. Similar applications of this analytical framework in other geographical and ecological contexts are needed, but a more general evaluation of the subject is also required, aimed to assess, on a broader systematic and ecological range, what specific traits of a carnivore are most related to its potential impact on prey species.

People and Wildlife: Zoning as a means of mitigating conflicts with large carnivores: principles and reality

ZONING: A CONCEPTUAL INTRODUCTION Conflicts in land use are an inevitable consequence of the presently high human population densities living on a planet of finite size. Within this finite space, land use planners struggle to integrate as many potentially conflicting elements as possible using two approaches: the multi-use concept where compatible land uses can occur in the same area, and zoning. Zoning is any form of geographically differentiated land management where different forms of potentially conflicting land use are given priority in different areas. For example, in modern town planning some areas are zoned as residential, others as commercial, industrial, agricultural or recreational. Zoning has been widely used in biodiversity conservation in the creation of national parks, nature reserves and other protected areas. The focus of this chapter is to examine how zoning can be applied to the conservation of large carnivores. This requires balancing the twin goals of conserving viable populations of large carnivores, and minimizing conflicts with humans, which is proving to be an exceptional challenge in our crowded world. LARGE CARNIVORES AND HUMAN ACTIVITY: CONFLICTS, COMPATIBILITY AND CONTEXT Conflict Zoning is only an issue because large carnivores cause conflicts with some human activities and interests throughout the world. These conflicts have been described in detail elsewhere (Woodroffe et al ., Chapter 1, Thirgood et al ., Chapter 2) but here we shall list the most important conflicts relevant for the discussion on zoning.

Implementation uncertainty when using recreational hunting to manage carnivores

Summary 1. Wildlife managers often rely on resource users, such as recreational or commercial hunters, to achieve management goals. The use of hunters to control wildlife populations is especially common for predators and ungulates, but managers cannot assume that hunters will always fill annual quotas set by the authorities. It has been advocated that resource management models should account for uncertainty in how harvest rules are realized, requiring that this implementation uncertainty be estimated. 2. We used a survival analysis framework and long‐term harvest data from large carnivore management systems in three countries (Estonia, Latvia and Norway) involving four species (brown bear, grey wolf, Eurasian lynx and wolverine) to estimate the performance of hunters with respect to harvest goals set by managers. 3. Variation in hunter quota‐filling performance was substantial, ranging from 40% for wolverine in Norway to nearly 100% for lynx in Latvia. Seasonal and regional variation was also high within country–species pairs. We detected a positive relationship between the instantaneous potential to fill a quota slot and the relative availability of the target species for both wolverine and lynx in Norway. 4. Survivor curves and hazards – with survival time measured as the time from the start of a season until a quota slot is filled – can indicate the extent to which managers can influence harvest through adjustments of season duration and quota limits. 5.  Synthesis and applications. We investigated seven systems where authorities use recreational hunting to manage large carnivore populations. The variation and magnitude of deviation from harvest goals was substantial, underlining the need to incorporate implementation uncertainty into resource management models and decisions‐making. We illustrate how survival analysis can be used by managers to estimate the performance of resource users with respect to achieving harvest goals set by managers. The findings in this study come at an opportune time given the growing popularity of management strategy evaluation (MSE) models in fisheries and a push towards incorporating MSE into terrestrial harvest management.

Quota hunting of Eurasian lynx in Norway: patterns of hunter selection, hunter efficiency and monitoring accuracy

Harvesting large carnivores is often a controversial issue and thus requires a higher precision than other types of recreational harvest. Despite this, management programmes are often initiated based on very limited knowledge about the state of the population and the composition and magnitude of the harvest. Here we analyse patterns of lynx harvest in Norway based on harvest data from 1994 to 2009. We found clear signs of sex-biased harvest rates, with males generally being more at risk. Further, harvest mortality rates increased with age among males but not among females. In general, the degree of quota filling was high, but there was a tendency for decreasing quota filling with increasing quotas. A population reconstruction of the Norwegian lynx population (1994–2004) based on a modified cohort analysis closely tracked the development in the official monitoring data, suggesting that the managers have access to relatively good information about the development of the population, at least at a larger spatial scale. Despite this, the population trajectory showed large temporal variation, and time lags in the management’s decision-making process are a likely cause of the observed patterns in the Norwegian lynx population.

Moose winter browsing affects the breeding success of great tits

Abstract In many areas, ungulates may have a large impact on the landscape due to their large body size and wide distribution. Moose (Alces alces) winter feeding has been carried out for a decade in parts of Hedmark County, southeast Norway. Previous studies have documented a gradual decline in browsing pressure away from the feeding stations. We utilized this gradient to study the indirect effects of moose browsing on a passerine bird, the great tit (Parus major). The downy birch (Betula pubescens) trees surrounding the feeding stations are subject to an intense browsing pressure gradually decreasing outwards. We put up nest boxes at feeding stations (i.e., sites of intense browsing pressure), with nearby controls with low visible browsing. The number of tall birch trees and the birch canopy cover was lower in browsed compared to control plots. Due to the reduced birch canopy cover, the total biomass of arthropods available around the nest boxes was lower in browsed compared to control plots. Great tit breeding pairs produced 1.3 fewer fledglings in browsed compared to control plots. We suggest this difference to be caused by lack of food in the browsed plots. Hence, moose browsing may reduce the breeding success of great tits through a series of knock-on effects through two other components of the boreal forest community.