High Deer Densities Research Articles

Effects of abundant white-tailed deer on vegetation, animals, mycorrhizal fungi, and soils

The last several decades have seen dramatic increases in ungulate populations worldwide, and white-tailed deer in the eastern United States currently exist at unprecedented densities in many areas. Numerous studies have demonstrated the effects of high densities of white-tailed deer on forest communities. However, few studies have simultaneously examined the effects of deer on multiple components of forest communities across trophic levels. Here, we simultaneously examine effects of excluding white-tailed deer on responses of woody and herbaceous vegetation, terrestrial and subterranean animals, mycorrhizal fungi, and soil characteristics. This study was conducted in a forest preserve with high deer densities in the central hardwoods region of the Midwestern US, using a series of replicated deer exclosures (15×15m) and adjacent unfenced controls that ranged in age from two to seven years. Despite significant tree recruitment inside exclosures, we recorded no native tree seedling recruitment in control plots. In addition, the growth rate of existing tree seedlings was significantly greater in exclosures than in controls, and the growth rate of invasive shrubs was approximately 30 times higher inside exclosures. Exclosures also had increased height, species diversity, and abundance of spring plants, and increased vegetation density in summer. We also found differences in terrestrial animals with higher densities of white-footed mice (Peromyscus leucopus) and dog ticks (Dermacentor variabilis) inside deer exclosures. However, there were no differences in salamanders or earthworms. Soil inside exclosures was significantly less compacted than in control plots despite the short period of deer exclusion, but there were no significant differences in soil nutrients or arbuscular mycorrhizal fungi. These results indicate that there are strong effects of high deer densities on all classes of understory vegetation and indirect effects on animals and soils. However, most belowground effects were nonsignificant, suggesting that responses of belowground communities to deer exclusion are weaker or slower to develop than aboveground effects.

Big game or big loss? High deer densities are threatening woody plant diversity and vegetation dynamics

Land-use change and current game management have favored an increasing population of wild ungulates (especially deer) in many regions of the Northern Hemisphere. Here, we assess the impact of high deer densities (>30 ind km−2) on the highly diverse woody vegetation of Mediterranean ecosystems, where big game have been favored for the last decades. We examine whether prolonged deer browsing (over 30 years) affected plant composition, diversity and dynamics of the original (non-browsed) vegetation. Deer browsing led to an average decrease of 30.4 % in woody plant diversity (species richness), due to a lack of regeneration for the most preferred plant species. Species belonging to early stages of succession (mostly Labiatae and Cistaceae) were non-preferred by deer. Conversely, the most preferred species belonged mainly to late stages of plant succession. Deer impact on Mediterranean shrublands is causing biotic homogenization of plant communities and is threatening vegetation dynamics by forcing it to return to earlier succession stages. Strict deer population control favouring larger trophies but lower offspring numbers together with an adequate habitat management (increasing grass and acorn availability) would be the most efficient measures to reverse this diversity loss. Restoration work seems only appropriate for the most vulnerable species. We highlight the need of sampling deer-free areas with low or null historical browsing to assess the real impact of deer on woody plant diversity and vegetation dynamics.

Eurasian lynx hunting red deer: is there an influence of a winter enclosure system?

As in several Central European areas, in the Bohemian Forest Ecosystem (Germany and the Czech Republic), fenced feeding enclosures are used for the winter management of red deer (Cervus elaphus), which is an important component of the Eurasian lynx’s (Lynx lynx) winter diet. Using GPS telemetry data, we tested whether (1) lynx hunted red deer mainly selecting for high prey densities and environmental characteristics like a good level of habitat heterogeneity, independently of the enclosures’ presence; (2) enclosures attracted lynx and (3) positively influenced their predation on red deer, being predictable and abundant prey sources throughout the winter; or (4) extremely high deer densities inside the enclosures rather negatively influenced lynx predation on this species. We first compared lynx space usage and predation on red deer inside and outside the enclosures. Then, we investigated the effects of the environment, prey densities and the enclosure distance for the area outside of enclosures. Prey densities positively influenced lynx space usage, whilst the probability of predation on red deer was highest at medium to low red deer densities. Habitat heterogeneity and terrain ruggedness influenced both lynx space usage and probability of predation on red deer. Regarding the effect of enclosures, the ratio “area used during night vs. daytime” was larger by a factor of 2 inside compared to outside enclosures, and the probability of predation on red deer was three times higher inside rather than outside of enclosures; however, these differences were not statistically significant, suggesting that the influence of the enclosures is not very pronounced.

Functional Responses and Resilience of Boreal Forest Ecosystem after Reduction of Deer Density

The functional trait-based approach is increasingly used to predict responses of ecological communities to disturbances, but most studies target a single taxonomic group. Here, we assessed the resilience of a forest ecosystem to an overabundant herbivore population by assessing changes in 19 functional traits for plant, 13 traits for ground beetle and 16 traits for songbird communities after six years of controlled browsing on Anticosti Island (Quebec, Canada). Our results indicated that plants were more responsive to 6 years of reduced browsing pressure than ground beetles and songbirds. However, co-inertia analysis revealed that ground beetle communities responded in a similar way than plant communities with stronger relationships between plant and ground beetle traits at reduced deer density, a pattern not detected between plant and songbird. High deer density favored plants species that reproduce vegetatively and with abiotic pollination and seed dispersal, traits implying little interaction with animal. On the other hand, traits found at reduced deer density mostly involved trophic interaction. For example, plants in this treatment had fleshy fruits and large seeds dispersed by birds or other animals whereas ground beetle species were carnivorous. Overall, our results suggest that plant communities recovered some functional components to overabundant herbivore populations, since most traits associated with undisturbed forests were reestablished after six years of deer reduction. The re-establishment of functional plant communities with traits involving trophic interaction induces changes in the ground-beetle trait community, but forest structure remains likely insufficiently heterogeneous to shift the songbird trait community within six years.

Comparative Morphology of Prickles of Rubus croceacanthus (Rosaceae) in Kashima Island and Its Neighbouring Areas

Kashima Island (32° 57? N, 132° 27? E) is a small island of southern Japan with high population density of sika deer (Cervus nippon). To ascertain whether heavy sika deer browsing has resulted in increased plant defences on the island, we conducted a morphological comparison of Rubus croceacanthus H. Lev. (Rosaceae) on Kashima Island and in the neighbouring areas on the mainland. We measured the length and density of the leaf and stem prickles. We found that the prickles of R. croceacanthus on Kashima Island were significantly longer and at a higher density than those in the neighbouring areas, suggesting that increased prickle length and density is an adaptive defence against sika deer browsing.

The impact of red deer management on liverworts associated with the mixed hepatic mat community and other terrestrial cryptogams

Background: Exclosure is often regarded as the most effective means of encouraging woodland regeneration in the presence of high deer densities. This has potential implications for terrestrial cryptogam diversity at a time when the Scottish Government is encouraging an increase in woodland cover. The hepatic mat assemblage at Coire Dhorrcail, Knoydart, is unique to the Scottish mainland in that it occurs from sea-shore to mountain summit throughout the full range of vegetation. No previous study has examined the response of this rare liverwort community to the absence of red deer.Aims: To compare the species richness, diversity, dominance and abundance of bryophytes and lichens either side of the twenty-year-old deer exclosure at Knoydart.Methods: Percentage cover of cryptogam species has been estimated from quadrats within paired sample plots at different altitudes on either side of the exclosure. Sampling was randomised at each stage. Simple linear models were used to analyse the data.Results: Succession within the exclosure has created conditions suitable for bulkier species of moss to attain local dominance, causing significant reduction of Herbertus hutchinsiae cover, cryptogam species richness and diversity.Conclusions: What is good for tree regeneration may be bad for terrestrial cryptogams. Careful consideration of existing biodiversity is necessary before exclosing large areas for woodland regeneration.

The Length and Density of Prickles on <i>Zanthoxylum ailanthoides</i> (Rutaceae): A Comparison of Japanese Islands with Different Sika Deer Browsing Pressures

To determine the effects of sika deer (Cervus nippon) browsing on the physical defences of the Japanese pricklyash “Zanthoxylum ailanthoides Sieb. et Zucc.” (Rutaceae), we compared the length and density of prickles on Japanese islands which were under different browsing pressures. We measured the length and density of prickles on the midribs, leaf rachis, and stems. We found that the prickles of Z. ailanthoides on Kashima island were not significantly longer or at higher densities than those in the neighbouring areas; the longest pickles at the highest densities were found on Akune island. The density of sika deer on Akune (ca. 520-600/km2) was higher than that on Kashima (ca. 38.5/km2), and consequently, Akune was under greater browsing pressure. Our results suggest that the increased length and density of prickles on Akune is a response by Z. ailanthoides to the high density of sika deer found on the island.

Morphological Study of <i>Glochidion obovatum</i> under Heavy Browsing Pressure by Sika Deer

To clarify the modification of physical defences of Glochidion obovatum Sieb. et Zucc., we compared the length of spine-like branches and frequency of lateral branches of G. obovatum between Kashima Island, which supports a high density of sika deer (Cervus nippon), and its neighbouring areas. The length of spine-like branches of G. obovatum in Kashima Island was not significantly longer than that of the neighbouring areas, but the frequency of lateral branches on the island was higher than that of the neighbouring areas. Since the branches of G. obovatum are heavily foraged by the sika deer, the shrub form of the species has evolved into the bonsai form, suggesting increased frequency of occurrence of lateral branches, which could develop as shoot-like branches. Thus, the observed features are facultative defence mechanisms of G. obovatum against heavy browsing in a small-sized island with very high density of sika deer.

Assessment of coyote–wolf–dog admixture using ancestry‐informative diagnostic SNPs

The evolutionary importance of hybridization as a source of new adaptive genetic variation is rapidly gaining recognition. Hybridization between coyotes and wolves may have introduced adaptive alleles into the coyote gene pool that facilitated an expansion in their geographic range and dietary niche. Furthermore, hybridization between coyotes and domestic dogs may facilitate adaptation to human-dominated environments. We genotyped 63 ancestry-informative single-nucleotide polymorphisms in 427 canids to examine the prevalence, spatial distribution and the ecology of admixture in eastern coyotes. Using multivariate methods and Bayesian clustering analyses, we estimated the relative contributions of western coyotes, western and eastern wolves, and domestic dogs to the admixed ancestry of Ohio and eastern coyotes. We found that eastern coyotes form an extensive hybrid swarm, with all our samples having varying levels of admixture. Ohio coyotes, previously thought to be free of admixture, are also highly admixed with wolves and dogs. Coyotes in areas of high deer density are genetically more wolf-like, suggesting that natural selection for wolf-like traits may result in local adaptation at a fine geographic scale. Our results, in light of other previously published studies of admixture in Canis, revealed a pattern of sex-biased hybridization, presumably generated by male wolves and dogs mating with female coyotes. This study is the most comprehensive genetic survey of admixture in eastern coyotes and demonstrates that the frequency and scope of hybridization can be quantified with relatively few ancestry-informative markers.

Density of Wild Prey Modulates Lynx Kill Rates on Free-Ranging Domestic Sheep

Understanding the factors shaping the dynamics of carnivore–livestock conflicts is vital to facilitate large carnivore conservation in multi-use landscapes. We investigated how the density of their main wild prey, roe deer Capreolus capreolus, modulates individual Eurasian lynx Lynx lynx kill rates on free-ranging domestic sheep Ovis aries across a range of sheep and roe deer densities. Lynx kill rates on free-ranging domestic sheep were collected in south-eastern Norway from 1995 to 2011 along a gradient of different livestock and wild prey densities using VHF and GPS telemetry. We used zero-inflated negative binomial (ZINB) models including lynx sex, sheep density and an index of roe deer density as explanatory variables to model observed kill rates on sheep, and ranked the models based on their AICc values. The model including the effects of lynx sex and sheep density in the zero-inflation model and the effect of lynx sex and roe deer density in the negative binomial part received most support. Irrespective of sheep density and sex, we found the lowest sheep kill rates in areas with high densities of roe deer. As roe deer density decreased, males killed sheep at higher rates, and this pattern held for both high and low sheep densities. Similarly, females killed sheep at higher rates in areas with high densities of sheep and low densities of roe deer. However, when sheep densities were low females rarely killed sheep irrespective of roe deer density. Our quantification of depredation rates can be the first step towards establishing fairer compensation systems based on more accurate and area specific estimation of losses. This study demonstrates how we can use ecological theory to predict where losses of sheep will be greatest, and can be used to identify areas where mitigation measures are most likely to be needed.

Long‐term biological legacies of herbivore density in a landscape‐scale experiment: forest understoreys reflect past deer density treatments for at least 20 years

Summary Ungulate browsers, when at high densities, are major drivers of vegetation change in forests world‐wide. Their effects operate via a variety of generalizable mechanisms related to plant palatability and relative growth rate with respect to browsing pressure. Though such impacts are obviously long‐lasting when they determine composition of tree regeneration, we document in a unique long‐term (30 year) experiment that biological legacies of initial deer density persist in the understorey herbaceous vegetation at least 20 years after deer densities were equalized. We sampled understorey vegetation in former clear‐cut areas where density of white‐tailed deer (Odocoileus virginianus) was manipulated (3.9–31.2 deer km−2) for 10 years (1979–1990), and stands experienced ambient deer density (ca. 10–12 deer km−2) for the next 20 years (1990–2010) to determine whether initial deer density treatments still influenced understorey vegetation in 30‐year‐old, closed‐canopy forests. Stands initially (1979–1990) exposed to higher deer densities had ca. five times higher fern cover and three times the seedling and forb cover in 2010, as well as significantly lower angiosperm species density, compared to stands initially exposed to lower deer densities. These results appear driven by deer avoidance of ferns, allowing them to expand at high deer density and sequester sites for decades. Synthesis. Our long‐term, experimental results show unequivocally that elevated deer densities cause significant, profound legacy effects on understorey vegetation persisting at least 20 years. Of relevance regionally and globally where high deer densities have created depauperate understoreys, we expect that deer density reduction alone does not guarantee understorey recovery; stands may need to be managed by removing recalcitrant understorey layers (e.g. ferns).

Estimating lichen volume and reindeer winter pasture quality from Landsat imagery

Reindeer and caribou are keystone species in the circumpolar region, and rely on lichens as their main winter forage to survive in some of the most extreme environments on Earth. Lichen mats, however, can be heavily overgrazed at high deer densities, triggering area abandonment or population declines. Although the species' management and conservation require precise information on the quality of winter grazing areas, no reliable and cost-efficient methods are available to date to measure lichen volume across wide and remote areas. We developed a new Lichen Volume Estimator, LVE, using remote sensing and field measurements. We used a Landsat TM land cover mask to separate lichen heath communities from other vegetation types and, therein, we predicted lichen volume from a two dimensional Gaussian regression model using two indexes: the Normalized Difference Lichen Index, NDLI (Band 5−Band 4/Band 5+Band 4), and the Normalized Difference Moisture Index, NDMI (Band 4−Band 5/Band 4+Band 5). The model was parameterized using 202 ground measurements equally distributed across a gradient ranging from 0 to 80 lichen dm3/m2 (R2=0.74 between predicted and observed ground measurements), and was validated with a ten-fold cross validation procedure (R2=0.67), which also showed a high parameter stability. The LVE can be a valuable tool to predict the quality of winter pastures for reindeer and caribou and, thus, help to improve the species' management and conservation.

Old-growth forest floor richness increases with red deer herbivory intensity

Herbivory is one of the most important biotic disturbance types globally and is important for community structure and composition through species filtering. In northern forest ecosystems the population densities of wild-ranging ungulates, which are managed through hunting, have reached historically high numbers. Conservation concerns frequently arise, both in media and scientific literature. One key question is whether increased deer densities negatively affect biodiversity and whether management should implement reduction in deer densities. Few studies have addressed wild herbivores-plant richness relationships using a full length gradient of herbivory. Such gradient approach where herbivory is studied from very low to very high intensity, may enable us to develop operational management guidelines for deer densities We recorded the ungulate herbivory intensities on the island Svanøy in west Norway across 10years and related this to the present plant richness of an old-growth pine-forest system, recording all plant species groups of the forest understory. The herbivory intensity-plant richness relationship followed a unimodally peaked curved, but plant richness was lower only at forest sites with artificially high red deer herbivory. Overall, the herbivory-richness relationships of functional groups fitted expectations in that the richness of low-growing functional groups as forbs, graminoids and mosses all increased within natural levels of herbivory intensities, whereas the richness of the taller growing woody species of the forest understory, dwarf-shrubs and young trees, decreased along the intensity gradient. We validated the gradient approach by experimental exclosure data. Management for relatively high deer densities may benefit the overall understory plant richness of such forest ecosystems at the expense of richness of woody plants. We suggest that the herbivory-induced reduction of the understory woody layer is the key to understand the overall increase in plant species richness.

The effect of white-tailed deer density on breeding songbirds in Delaware

Most population goals for white-tailed deer (Odocoileus virginianus) are based solely on deer data, with little consideration for other parts of the ecosystem. A wider ecological approach is needed for more justifiable target deer densities. We investigated the use of birds as coarse-scale indicators to determine an ecological carrying capacity for deer management by studying the relationship between the forest bird community and deer density in Delaware, USA. Using Breeding Bird Survey data from 2005 to 2009, targeted point-count data from 2008 to 2009 and Division of Fish and Wildlife deer-density data from the same time periods, we compared avian species richness and relative abundance with deer density. We divided deer densities into low (≤10 deer/km2), moderate (11–19 deer/km2), and high (≥20 deer/km2) categories. We placed birds into 6 deer-sensitive guilds: interior forest obligates, ground nesters, shrub nesters, ground gleaners, low-canopy foragers, and Neotropical migrants, as well as 1 “guild” that consisted of species found to be sensitive to deer density in past literature. The abundance or richness of most guilds and species did not differ by deer density. However, there were 1.08 more shrub nesters and 0.55 more species of shrub nesting birds in low-deer-density areas than in high-deer-density areas. Areas of moderate and low deer densities had ≥0.35 more species of low-canopy foragers than did areas of high deer densities. Low-deer-density areas had ≥0.59 more individual Neotropical migrants compared with moderate- or high-deer-density areas. Similarly, areas of low deer densities had ≥0.49 more migrant species than did areas of higher densities. Low-deer-density areas had ≥0.17 more ovenbirds compared with high- and moderate-deer-density areas. Great crested flycatchers (Myiarchus crinitus) had 3 times greater odds of being found in low-deer-density areas than in high-deer-density areas. Chipping sparrows (Spizella passerina), Acadian flycatchers (Empidonax virescens), and red-eyed vireos (Vireo olivaceus) all had 2 times greater odds of being found in low-deer-density areas than high-deer-density areas. Our results suggest that areas in Delaware with densities of <20 deer/km2 have the greatest avian richness and abundance. These findings are the first step toward determining an ecological carrying capacity for white-tailed deer. © 2013 The Wildlife Society.

Spatial and seasonal variation in the prevalence of Anaplasma phagocytophilum and Borrelia burgdorferi sensu lato in questing Ixodes ricinus ticks in Norway.

BackgroundUnderstanding the variation in prevalence of Borrelia burgdorferi sensu lato (Lyme Borreliosis Spirochaetes, LBS) and Anaplasma phagocytophilum (causing tick-borne fever in ruminants and human granulocytic ehrlichiosis) in ticks is vital from both a human and an animal disease perspective to target the most effective mitigation measures. From the host competence hypothesis, we predicted that prevalence of LBS would decrease with red deer density, while prevalence of A. phagocytophilum would increase.MethodsBased on a sample of 112 adult and 686 nymphal Ixodes ricinus ticks collected with flagging during questing from 31 transects (4–500 m long) corresponding to individual seasonal home ranges of 41 red deer along the west coast of Norway, we tested whether there were spatial and seasonal variations in prevalence with a special emphasis on the population density of the most common large host in this area, the red deer (Cervus elaphus). We used a multiplex real-time PCR assay for detection of A. phagocytophilum and LBS.ResultsPrevalence of LBS was higher in adult female ticks (21.6%) compared to adult male ticks (11.5%) and nymphs (10.9%), while prevalence was similar among stages for prevalence of A. phagocytophilum (8.8%). Only partly consistent with predictions, we found a lower prevalence of LBS in areas of high red deer density, while there was no relationship between red deer density and prevalence of A. phagocytophilum in ticks. Prevalence of both bacteria was much higher in ticks questing in May compared to August.ConclusionsOur study provides support to the notion that spatial variation in host composition forms a role for prevalence of LBS in ticks also in a northern European ecosystem, while no such association was found for A. phagocytophilum. Further studies are needed to fully understand the similar seasonal pattern of prevalence of the two pathogens.

Demographic characterization and social patterns of the Neotropical pampas deer

The most endangered subspecies of pampas deer Ozotoceros bezoarticus uruguayensis is an endemic cervidae of the Uruguayan temperate grasslands. The aim of our study was to assess the demographic trends, grouping structure and dynamic of this small and isolated population. We surveyed the population during seven years and detected an average of 117 (+ 72.7 SD) individuals (44 censuses). The average population structure observed was 55% adult females, 34% adult males, 10% juveniles, and 1% fawns, with a low recruitment rate of 0.11. The pampas deer is a gregarious cervidae with 62% of individuals being observed within groups of at least three animals. Nevertheless we observed substantial differences on group size and composition based on sex, reproductive status, season and trophic resources availability. The population dynamics showed significant changes around the year in the sexual aggregation-segregation pattern, corresponding with reproductive and physiological status. The mean density on this population (11 deer/ km2) is the highest reported for the species. Comparable data, from other populations, showed a significant correlation between density and sex ratio, with a reduction in the proportion of males with higher deer densities. An action plan for this endangered population should include initiatives involving private landowners, and guidelines to improve the deer habitat.

Higher sika deer density is associated with higher local abundance ofHaemaphysalis longicornisnymphs and adults but not larvae in central Japan

Haemaphysalis longicornis (Acari: Ixodidae) is one of the most common and important arthropod disease vectors in Japan, carrying Japanese spotted fever and bovine theileriosis. The recent expansion of sika deer (Cervus nippon, Artiodactyla: Cervidae) populations, the most common wild host of H. longicornis, has also caused concern about increasing the risk of vector-borne diseases in Japan. We used generalized linear mixed model analysis to determine the relative contribution of deer density and other biological and abiotic factors on the abundance of H. longicornis ticks questing at each developmental stage. A total of 6223 H. longicornis adults, nymphs, and larvae were collected from 70 sites in three regions of central Japan. The abundance of questing adult and nymphal ticks was associated with deer density and other biotic and abiotic factors. However, the abundance of questing larvae showed no association with deer density but did show an association with other biotic and abiotic factors. These findings show that a high density of deer along with other biotic and abiotic factors is associated with increased risk of vector-borne diseases through amplified local abundance of questing nymphal and adult H. longicornis. Further, questing larvae abundance is likely regulated by environmental conditions and is likely correlated with survival potential or the distribution of other host species.

Indirect Effects of Pandemic Deer Overabundance Inferred from Caterpillar‐Host Relations

Externally feeding phytophagous insect larvae (i.e., caterpillars, here, larval Lepidoptera and sawflies, Hymenoptera: Symphyta) are important canopy herbivores and prey resources in temperate deciduous forests. However, composition of forest trees has changed dramatically in the eastern United States since 1900. In particular, browsing by high densities of white-tailed deer (Odocoileus virginianus) has resulted in forests dominated by browse-tolerant species, such as black cherry (Prunus serotina), and greatly reduced relative abundance of other tree species, notably pin cherry (Prunus pensylvanica) and birches (Betula spp.). To quantify effects of these changes on caterpillars, we sampled caterpillars from 960 branch tips of the 8 tree species that comprise 95% of trees in Allegheny hardwood forests: red maple (Acer rubrum), striped maple (Acer pensylvanicum), sugar maple (Acer saccharum), sweet birch (Betula lenta), yellow birch (Betula allegheniensis), American beech (Fagus grandifolia), black cherry, and pin cherry. We collected 547 caterpillar specimens that belonged to 66 Lepidoptera and 10 Hymenoptera species. Caterpillar density, species richness, and community composition differed significantly among tree species sampled. Pin cherry, nearly eliminated at high deer density, had the highest density and diversity of caterpillars. Pin cherry shared a common caterpillar community with black cherry, which was distinct from those of other tree hosts. As high deer density continues to replace diverse forests of cherries, maples, birches, and beech with monodominant stands of black cherry, up to 66% of caterpillar species may be eliminated. Hence, deer-induced changes in forest vegetation are likely to ricochet back up forest food webs and therefore negatively affect species that depend on caterpillars and moths for food and pollination.

Surveillance and movements of Virginia opossum (Didelphis virginiana) in the bovine tuberculosis region of Michigan

Wildlife reservoir hosts of bovine tuberculosis (bTB) include Eurasian badgers (Meles meles) and brushtail possum (Trichosurus vulpecula) in the UK and New Zealand, respectively. Similar species warrant further investigation in the northern lower peninsula of Michigan, USA due to the continued presence of bTB on cattle farms. Most research in Michigan, USA has focused on interactions between white-tailed deer (Odocoileus virginianus) and cattle (Bos taurus) for the transmission of the infectious agent of bTB, Mycobacterium bovis, due to high deer densities and feeding practices. However, limited data are available on medium-sized mammals such as Virginia opossum (Didelphis virginiana; hereafter referred to as opossum) and their movements and home range in Michigan near cattle farms. We conducted surveillance of medium-sized mammals on previously depopulated cattle farms for presence of M. bovis infections and equipped opossum with Global Positioning System (GPS) technology to assess potential differences in home range between farms inside and outside the bTB core area that has had cattle test positive for M. bovis. On farms inside the bTB core area, prevalence in opossum was comparable [6%, 95% confidence interval (CI) 2.0-11.0] to prevalence in raccoon (Procyon lotor; 4%, 95% CI 1.0-9.0, P=0.439) whereas only a single opossum tested positive for M. bovis on farms outside the bTB core area. The prevalence in opossum occupying farms that had cattle test positive for M. bovis was higher (6.4%) than for opossum occupying farms that never had cattle test positive for M. bovis (0.9%, P=0.01). Mean size of home range for 50% and 95% estimates were similar by sex (P=0.791) both inside or outside the bTB core area (P=0.218). Although surveillance efforts and home range were not assessed on the same farms, opossum use of farms near structures was apparent as was selection for farms over surrounding forested habitats. The use of farms, stored feed, and structures by opossum, their ability to serve as vectors of M. bovis, and their propensity to ingest contaminated sources of M. bovis requires additional research in Michigan, USA.

A geostatistical approach to spatial density distributions of sika deer (Cervus nippon)

Sika deer (Cervus nippon) cause serious damage to trees in Japanese forests. Browsing, bark stripping, and tree abrasion with antlers account for 50% of total wildlife damage over the past decade. The extent of forest damage depends on deer population density. We determined the spatial distribution of sika deer population density on Mt. Hiko (Fukuoka Prefecture, southwestern Japan). We also investigated changes in population density distribution over time. Determinants of population density were examined, with particular emphasis on the hunting cull. Deer densities in 1999 and 2004 were estimated by fecal pellet counts at 86 sites. We used kriging, a geostatistical technique that is a component of geographic information systems, to interpolate site-specific point data over large areas of landscape. Mapping procedures showed that high-density (≥30.0 deer km−2) and low-density sections of landscape (≤10.0 deer km−2) decreased in areal extent between 1999 and 2004. Contractions of high-density sections were attributable to intensive hunting. In low-density landscape sections, reduced hunting pressure allowed increased persistence of adult animals whose high fecundity led to population growth and higher deer densities. Landscape tracts with medium deer densities (10.0–30.0 deer km−2) expanded, adding further difficulties to the task of wildlife management. Given the scale of the problems caused by deer, it is clear that reliable estimates of population size across space and time are essential components of the wildlife manager's toolbox.