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Distribution, quantity and quality of food resources affect the diet and several other life-history traits of large mammals. Supplemental feeding of wildlife has high potential for influencing the behaviour and diet of opportunistic omnivores, such as bears. Supplemental feeding of brown bears Ursus arctos is a common practice in several European countries, but the effects of this controversial and expensive management measure on bear diet and behaviour are poorly understood. We analysed 714 brown bear scats collected throughout the year in three regions of Slovenia with different densities of supplemental feeding sites. Supplemental food was the most important food category in the bear diet and represented 34% of the annual estimated dietary energy content (maize: 22%, livestock carrion: 12%). The proportion of supplemental food in the diet varied with season and region, being highest in spring and in the region with the highest density of feeding sites. However, considerable seasonal changes in bear diet, despite year-round access to supplemental food, suggest that bears prefer high-energy natural food sources, particularly insects, fruits, and hard mast, when available. Despite high availability and use of supplemental food, human—bear conflicts are frequent in Slovenia. In addition, evidence from earlier studies suggests that changes in diet and foraging behaviour due to supplemental feeding may affect several aspects of bear biology and in some cases increase the probability of human—bear conflicts. Thus, we caution against promoting unconditional supplemental feeding as a measure to prevent or reduce human—bear conflicts.
Habitat selection by mammalian carnivores may be driven by prey availability, physical characteristics of the habitat, and landscape context. However, the cues used by carnivores to select habitat are often unclear. We examined the seasonal diet of American mink Neovison vison and determined if the abundance of a primary prey, crayfish, was an important driver of habitat use during summer in an agricultural landscape in Illinois. We also evaluated effects of stream size, water depth, riparian buffer width, and urbanization on occupancy of stream segments by mink. We collected mink scats during three seasons and tested for seasonal differences in the percentage of occurrence and volume percentage of prey classes in the diet of mink. Crayfish remains were the dominant component of mink scats during summer. In summer 2012, we performed occupancy surveys for mink and concurrently measured crayfish densities and habitat features in 59 stream segments. Site occupancy by mink was related positively to presence of local areas with high crayfish concentrations (hotspots) instead of local habitat characteristics that might indicate high prey densities. Mink also were associated negatively with degree of urbanization and stream size. Our study highlights the effectiveness of integrating data on diets and occupancy modeling to obtain insights on cues used by carnivores to select habitat.
Wildlife managers often need tangible evidence of density dependence in populations to support decision making. Field experimentation to identify density dependent effects is often cost and time prohibitive. Thus, assimilation of existing knowledge into a balance of probabilities can serve as a surrogate for experimental research. A case study of such a process is found in the mule deer Odocoileus hemionus herds of Colorado. Wildlife managers and hunters expressed concern over a recent decline in western Colorado mule deer herds, yet the underlying cause of this decline is yet to be determined. In response to this management concern, we conducted a review of scientific evidence on Colorado's mule deer population dynamics. This review was done in the context of a conceptual model that portrays population growth as a function of population size, per capita growth rate and population carrying capacity. Similar declines that occurred during the 1960s and early 1990s resulted in similar reviews that identified research and management topics that would benefit mule deer. These topics included: harvest, predation, intraspecific competition, disease, interspecific competition, and habitat loss and degradation. Between the late 1990s and present time, many of these topics were addressed by research. The conventional working hypothesis in Colorado is that mule deer herds are limited by winter range habitat. We identify new gaps in knowledge and suggest potential, future research topics, as well as potential management strategies. We suggest a focus on integrated studies of multiple herbivores with density reduction experiments to address intra- and inter- specific competition. In addition, we suggest focused experiments that address the roles of mountain lion predation, black bear predation, and disease in mule deer population dynamics.
This article is a tutorial for the R-package carcass. It starts with a short overview of common methods used to estimate mortality based on carcass searches. Then, it guides step by step through a simple example. First, the proportion of animals that fall into the search area is estimated. Second, carcass persistence time is estimated based on experimental data. Third, searcher efficiency is estimated. Fourth, these three estimated parameters are combined to obtain the probability that an animal killed is found by an observer. Finally, this probability is used together with the observed number of carcasses found to obtain an estimate for the total number of killed animals together with a credible interval.
Species of national conservation concern require management action to reduce the threat of extinction. As part of its obligations to reduce national loss of biodiversity, the Norwegian authority for nature management (The Norwegian Environment Agency) published an action plan in 2010 for one of these species, the Slavonian grebe Podiceps auritus. The American mink Neovison vison, a non-native, invasive species with wide spread negative effects on native fauna, was highlighted as a major potential treat. We used an adaptive management approach that included management trials with the aim to assess whether mink predation is likely to be affecting grebe numbers significantly. We monitored mink activity, and put in place mink control measures at three of our seven study lakes. We then used 35 pairs of artificial nests, with one of each pair equipped with cameras, to measure predation at all seven lakes. The combined use of progressive experiments in an adaptive management/monitoring framework showed that mink activity was generally low with a mean activity at raft stations of between 0.41–1.22 per lake (n = 5), a range of zero to three excavations executed as a result of hunting (n = 3), and no incidences of mink nest predation (n = 35). Hence we conclude that mink is presently not likely to be a significant negative factor on grebe breeding success in the targeted lakes. We found a high nest predation rate by hooded crow with 18 of 21 identified predation events being identified to this species. Future effort should investigate non mink related threats to the Slavonian grebe such as the role of hooded crow in nest predation. This case study exemplifies the usefulness of the adaptive management/monitoring framework as a powerful means of testing hypotheses and to inform management, especially when knowledge of the focal system is poor.
In several west European countries, the distribution of hedgehogs Erinaceus europaeus is declining. In the UK, predation by the European badger Meles meles is considered to be the main death cause of hedgehogs. In the Netherlands, badger density is rising, which suggests the same cause for the decline. As landscape and land use largely differ between the UK and the Netherlands, we investigated the relationship between the distribution of badgers and hedgehogs in the Netherlands. Therefore, we used the presence of badgers and hedgehogs recorded in the period 2007–2010 in grid cells of 1 km2, together with environmental variables, i.e. land-use types and soil types, to describe the habitat of both species. Although the distribution of badgers in the Netherlands is still limited, we found indeed a negative effect of badger presence on hedgehog presence. We also found a positive effect of urban area, recreational land use and roads on hedgehog presence, whereas these types had a negative effect on badger presence. Our study suggests that hedgehogs in the Netherlands are nowadays found close to human occupation, possibly due to the negative effect of badgers. These results contribute to understanding of the declining distribution of hedgehogs in western Europe.