Fence-Line Contact Between Wild and Farmed Cervids in Colorado: Potential for Disease Transmission

Abstract: Direct and indirect contact between wild and farmed cervids along perimeter fences may play a role in transmission of diseases like chronic wasting disease (CWD), but no studies have quantified such interactions. At 9 high-fenced commercial elk (Cervus elaphus) farms in Colorado, USA, during October 2003 to January 2005, we used animal-activated video to estimate rates of fence-line use by wild cervids, rates of direct contact between farmed and wild cervids, and probability of direct contact when wild cervids were present. We recorded 8-fold-more wild elk per unit time than mule deer (Odocoileus hemionus) at fence lines. Depending on site, we recorded 0.66 to 46.90 wild elk per 1,000 hours of camera monitoring. We documented 77 interactions between wild and farmed elk involving naso-oral contact and no contact between wild mule deer and farmed elk. Rate of direct contact ranged from 0.00 to 1.92 direct contacts per 1,000 hours of camera monitoring among sites. Given recorded presence of wild elk, estimated probability of observing direct contact during a 2-minute video recording ranged from 0.00 to 0.11 among sites. Risk of direct contact was about 3.5 times greater for single woven-wire fence compared with offset electric fence attached to a single woven-wire fence. We observed no direct contact through double woven-wire fences. Because little is currently known about infection rates associated with infection mechanisms, we cannot infer a level of CWD infection risk from our results, but some form of double fencing should reduce potential for direct and indirect transmission of disease into or out of elk farms.     

Evaluation of Electric Fencing to Inhibit Feral Pig Movements

Abstract: Natural resource managers and agricultural producers are seeking innovative tools to minimize damages caused by rapidly expanding feral pig (Sus scrofa) populations. One tool that has received little scientific inquiry is the use of exclusion fences to protect economically and ecologically sensitive areas. Our objectives were to evaluate the ability of electric fencing to minimize feral pig movements in a captive setting as well as in rangeland and agriculture land. In captivity, we tested a 1-, 2-, and 3-strand electric fence. In our captive trial, we found 65% fewer intrusions (F_2,18 = 20.46, P < 0.001) for electric fences (x̄ = 12.4, SE = 2.8) compared with nonelectric fences (x̄ = 35.6, SE = 6.9). We found no difference (F_2,9 = 1.85, P = 0.212) for 1-strand (x̄ = 28.1, SE = 7.8), 2-strand (x̄ = 14.2, SE = 3.2), and 3-strand (x̄ = 16.9, SE = 4.3) electric fences. However, we found 50% and 40% fewer crossings for the 2- and 3-strand fences, respectively, compared with the 1-strand fence. In our rangeland trial, we found 49% fewer intrusions (F_2,18 =4.39, P = 0.028) into bait stations with a 2-strand electric fence (x̄ =4.1, SE = 1.8) compared with no fence (x̄ =8.1, SE = 2.4). Finally, in our agriculture trial, we found 64% less damage (X²₂ = 5.77, P = 0.016) to sorghum crops with a 2-strand electric fence (x̄ = 4.48, SE = 0.01%) compared with no electric fence (x̄ = 12.46, SE = 0.03%). Furthermore we found no (X¹₁ = 3.72, P = 0.054) wildlife pathways in areas with an electric fence (x̄ = 0.0, SE =0.0) compared with no fence (x̄ = 2.4, SE= 1.3). No electric fence design we tested was 100% pig-proof However, we found electric fencing restricted feral pig movements. Combining electric fencing with other damage control methods in an integrated management program may be the best method for alleviating feral pig damages.     

Survival and fidelity of an enclosed white-tailed deer population using capture–recapture-reporting data

The number of animal populations enclosed by impermeable fences has increased, which poses issues related to the behavior of individuals and populations. Despite the increased number of fenced enclosures, there is a paucity of survival and fidelity data on white-tailed deer (Odocoileus virginianus) from fenced enclosures. Therefore, we examined marked deer recaptures and resightings over 13 years for an enclosed population of white-tailed deer in Oklahoma, USA, to estimate survival and fidelity parameters. We found that a step model was the best model of survival for both sexes. Survival of females and males was greater after hunting was suspended. Average female survival was 77% before hunting was suspended but increased to 98% after. Male survival was also greater after (99%) hunting was suspended compared to before (58%). Females exhibited greater site fidelity (84–94%) than males for all age groups except old individuals, which showed similar site fidelities for males and females. Fidelity was highest for old males (85%), followed by adult (74%), fawn (61%), and yearling males (56%). Our high-tensile electric fence allowed management goals to be achieved through increased survival while potentially maintaining genetic diversity through the exchange of limited numbers of individuals from surrounding areas. However, if the goal is to confine deer to limit disease spread or protect sensitive areas (e.g., airports) from deer encroachment, then other fence designs may be necessary, because our fence was not completely effective at controlling deer movements for these purposes.     

Pest fencing or pest trapping: A bio‐economic analysis of cost‐effectiveness

Scofield et al. discredited the utility of pest‐exclusion fences for restoring biodiversity partly on the grounds of unquantified costs and benefits. We estimated the discounted costs of mammal exclusion fences, semi‐permeable (‘leaky’) fences and trapping, over 50 years and adjusted costs by their observed effectiveness at reducing mammalian predator abundance. We modelled data from two large predator management programmes operated by the New Zealand Department of Conservation. Using typical baseline costs and predator control efficacies (scale 0 to 1), the model predicted that an exclusion fence (efficacy 1.0) is the cheapest and most cost‐effective option for areas below about 1 ha, a leaky fence (efficacy 0.9) is most cost‐effective for 1–219 ha, and trapping (efficacy 0.6, based on 0.2 traps per hectare and a 1500‐m buffer to reduce predator reinvasion) for areas above 219 ha. This ranking was insensitive to adjustments in efficacy, but reducing efficacy of leaky fences to 0.8 or increasing trapping efficacy to 0.7 reduced the cost‐effective range of leaky fences by about 90 ha. Reducing trap maintenance costs from $300 to $100 per trap per year (e.g. using long‐life lures), or reducing trap buffer widths to 500 m, significantly elevated trapping as the most cost‐effective method for areas greater than 11–15 ha. These results were largely consistent with an ecological measure of effectiveness based on observed rates of recovery of two indigenous skink species inside exclusion fences or with trapping. The results support criticisms that exclusion fences are generally not cost‐effective, but highlight the value of considering cheaper leaky designs for small‐ to medium‐sized areas. Because this study is based largely on reductions in predator abundance, it has general application to broader biodiversity protection interests, but not to indigenous species that are highly sensitive to predation and only ever adequately protected on the mainland by exclusion fences.     

Multi-scale assessment of greater sage-grouse fence collision as a function of site and broad scale factors

Previous research in Europe and North America suggested grouse are susceptible to collision with infrastructure, and anecdotal observation suggested greater sage-grouse (Centrocercus urophasianus) fence collision in breeding habitats may be prevalent. However, no previous research systematically studied greater sage-grouse fence collision in any portion of their range. We used data from probability-based sampling of fences in greater sage-grouse breeding habitats of southern Idaho, USA, to model factors associated with collision at microsite and broad spatial scales. Site-scale modeling suggested collision may be influenced by technical attributes of fences, with collisions common at fence segments absent wooden fence posts and with segment widths >4 m. Broad-scale modeling suggested relative probability of collision was influenced by region, a terrain ruggedness index (TRI), and fence density per square km. Conditional on those factors, collision counts were also influenced by distance to nearest active sage-grouse lek. Our models provide a conceptual framework for prioritizing sage-grouse breeding habitats for collision mitigation such as fence marking or moving, and suggest mitigation in breeding habitats should start in areas with moderate-high fence densities (>1 km/km²) within 2 km of active leks. However, TRI attenuated other covariate effects, and mean TRI/km² >10 m nearly eliminated sage-grouse collision. Thus, our data suggested mitigation should focus on sites with flat to gently rolling terrain. Moreover, site-scale modeling suggested constructing fences with larger and more conspicuous wooden fence posts and segment widths <4 m may reduce collision. © 2012 The Wildlife Society.     

Exclosure fences around nests of imperiled Florida Grasshopper Sparrows reduce rates of predation by mammals

Increasing nest survival by excluding predators is a goal of many bird conservation programs. However, new exclosure projects should be carefully evaluated to assess the potential risks of disturbance. We tested the effectiveness of predator exclosure fences (hereafter, fences) for nests of critically endangered Florida Grasshopper Sparrows (Ammodramus savannarum floridanus) at a dry prairie site (Three Lakes; 2015–2018) and a pasture site (the Ranch; 2015–2016) in Osceola County, Florida, USA. We installed fences at nests an average of 8 days after the start of incubation, and nest abandonment after fence installation was rare (2 of 149 installations). Predation was the leading cause of failure for unfenced nests at both sites (48–73%). At Three Lakes, nest cameras revealed that mammals and snakes were responsible for 61.5% and 38.5% of predation events, respectively, at unfenced nests. Fences reduced the daily probability of predation (0.016 for fenced nests vs. 0.074 for unfenced nests). The probability that a fenced nest would survive from discovery to fledging was more than double that of unfenced nests (60.4% vs. 27.7%). However, we found no difference in daily nest survival at the Ranch between the year before nests were fenced (2015; 0.874) and the year when all but one nest were fenced (2016; 0.867) because red imported fire ants (Solenopsis invicta) were responsible for 86% of predation events at fenced nests at the Ranch. The use of cameras at fenced nests revealed that site‐specific differences in nest predators explained variation in fence efficiency between sites. Our fence design may be useful for other species of grassland birds, but site‐specific predator communities and species‐specific response of target bird species to fences should be assessed before installing fences at other sites.     

Response of Deer to Containment by a Poly-Mesh Fence for Mitigating Disease Outbreaks

Abstract: Rapidly deployable and effective methods are needed to contain free-ranging deer (Odocoileus spp.) during acute disease outbreaks. We evaluated efficacy of a 2.1-m-tall polypropylene mesh (poly-mesh) fence for containing ≥15 free-ranging white-tailed deer (O. virginianus) within a 42-ha area in eastern Nebraska, USA. We observed a 99% decrease in deer leaving the enclosure area after we installed fencing (1 deer jumped; 0.02 deer/hr) compared with prefence rates (5.26 deer/hr). However, 8 deer (53% of censused population) escaped the enclosure during a census drive after our study. Poly-mesh fencing may be effective in temporarily containing free-ranging deer during minimally disruptive deer removal actions such as trapping or sharpshooting.     

Electric Fencing as a Measure to Reduce Moose-Vehicle Collisions

Abstract: We tested the effectiveness of electric fences to reduce moose (Alces alces)-vehicle collisions in 2 fenced sectors (5 km and 10 km) using weekly track surveys and Global Positioning System telemetry. Number of moose tracks along highways decreased by approximately 80% following fence installation. Only 30% (16/53) of moose tracks observed on the road side of the fence were left by moose that crossed an operational fence; moose mostly entered the fenced corridor through openings (e.g., secondary roads) or at fence extremities. Electric fences also prevented 78% (7/9) of collared moose from crossing the highway in fenced sectors. Fences were less effective during occasional power failures. We suggest that circuit breakers should be used to prevent power failures and that there should be no opening along the fence line unless anti-ungulate structures are used.     

The effects of grazers on the performance of individuals and populations of scarlet gilia,Ipomopsis aggregata

Summary I. aggregata exhibits considerable powers of regrowth following removal of its primary shoot by herbivores, but we found no evidence of overcompensation (i.e. of significantly higher plant performance where plants were exposed to ungulate herbivory) in a comparison between individuals on grazed and ungrazed sides of exclosure fences, in a comparison between artificially clipped and control plants in one population in the Okanagan National Forest, or in comparisons between grazed and ungrazed plants in 14 natural populations. We tested whether ungulate grazing affects the population size of Ipomopsis aggregata by comparing populations inside and outside deer exclosures at 7 sites in the Western United States. We found consistent, highly significant differences in plant population density on the grazed and ungrazed sides of these exlosure fences. Plant density was a modal 25-fold higher on the protected side of the fence, suggesting that exposure to ungulate grazing increases plant death rates at some stage in the life cycle. Our results show that the presence of ungulate grazers leads to a substantial decrease in plant density despite the fact that grazing on young bolting shoots has very little influence on fruit production. Since this decrease in population density is not correlated with a decrease in the fecundity of individuals, it must instead be due to other direct and indirect effects of ungulate grazers.     

Differential response of mammals to agricultural fences — The effects of species vagility and body size

An increase in wolf populations during the 1990s in North-Eastern Israel compelled livestock growers to establish fenced calving enclosures to minimize cattle predation. We hypothesized that such fences form barriers to animals traversing the landscape, to which various wildlife species may respond differentially. In order to test this, an array of line transects were established near six enclosures at which scat pellets were monitored for 23 months. We identified 1496 pellets, belonging mainly to medium or large mammal species. To estimate pellet abundance and quantify mammal activity levels we used N-mixture models. We tested the performance of seven models assuming two abundance distribution functions: Poisson and zero-inflated Poisson (ZIP) distribution models which evaluated different combinations of explanatory variables: effects of time, enclosure and transect. Model selection was performed using the Akaike Information Criterion (AIC). Pellet counts and mean estimated abundance were greater in transects external to the enclosures, for all species combined, mountain gazelle (Gazella gazella) and wild boar (Sus scrofa). Additionally, two behavioral responses to the presence of protective fences were observed. Outside the enclosures a U-shaped response of decrease in abundance at a distance of 50 m from the fence followed by an increase towards the distant transects at 200–700 m from the fence. Inside the calving enclosures a decreasing abundance response was observed, which was negatively correlated with distance from the fence. This study identifies the spatial effects emerging from the presence of protective fences as habitat-fragmenting agents. It suggests that a protective fence imposes a habitat-independent behavioral filter at the landscape level which could be related to species vagility and body size. Inconsistent activity responses of the different species to the presence of fences are repeatedly observed, providing support for our initial hypothesis.     

Reptile bycatch in a pest-exclusion fence established for wildlife reintroductions

Conservation fences have been used as a tool to stop threatening processes from acting against endangered wildlife, yet little is known of the impacts of fences on non-target native species. In this study, we intensively monitored a pest-exclusion fence for 16 months to assess impacts on a reptile community in south-eastern Australia. We registered 1052 reptile records of six species along the fence. Encounters and mortality were greatest for eastern long-necked turtles (Chelodina longicollis), whereas impacts on lizards (Tiliqua rugosa, Tiliqua scincoides, Pogona barbata, Egernia cunninghami) and snakes (Pseudonaja textilis) were more moderate. We recorded several Chelodina longicollis recaptures at the fence and many of these were later found dead at the fence, indicating persistent attempts to navigate past the fence. We conservatively estimate that the fence resulted in the death of 3.3% and disrupted movements of 20.9% of the turtle population within the enclosure. Movement disruption and high mortality were also observed for turtles attempting to enter the nature reserve, effectively isolating the reserve population from others in the wider landscape. Of 98 turtle mortalities, the most common cause of death was overheating, followed by predation, vehicular collision, and entanglement. Turtle interactions were clustered in areas with more wetlands and less urban development, and temporally correlated with high rainfall and solar radiation, and low temperature. Thus, managers could focus at times and locations to mitigate impacts on turtles. We believe the impact of fences on non-target species is a widespread and unrecognized threat, and suggest that future and on-going conservation fencing projects consider risks to non-target native species, and where possible, apply mitigation strategies that maintain natural movement corridors and minimize mortality risk.     

Influence of pitfall versus Longworth livetraps, bait addition, and drift fences on trap success and mortality of shrews

Pitfall trapping is believed to be the most efficient method for capturing shrews (Sorex spp.); however, Longworth live-traps have been used successfully in North America and Great Britain. Due to high metabolic rates, previous attempts to livetrap shrews have been faced with very high (exceeding 95 % in some circumstances) mortality rates. Here we report the results of two experiments attempting to integrate successful livetrapping of shrews into standard rodent trapping protocols. In Experiment 1 we compared efficiency of pitfall and Longworth live-traps operated with drift fences on 1-ha trapping grids for capturing vagrant shrews (Sorex vagrans) on agricultural set-asides in Delta, British Columbia, Canada. A total of 100 trap stations, on each of three trapping grids, were equipped with a 3-m-long drift fence and randomly assigned either one pitfall at the centre of each fence, or two Longworth traps, one at each end of the fence. In addition, we randomly selected 50 % of trap stations and provided 6 g of mealworms (Tenebrio molitor) larvae as bait. In response to high mortality rates, we varied the frequency of trap checks, with intervals of 12–14 h (long), 6–9 h (medium) and 3–4 h (short). Contrary to our predictions, Longworth traps captured significantly more shrews than pitfall traps. We observed the highest mean mortality rates in traps without mealworms, checked at long intervals. Shrews in mealworm-baited traps checked at short intervals experienced no mortality. Mortality rates in mealworm-baited traps checked at short and medium intervals were similar (t?=??1.33, P?=?0.20, Bonferroni-corrected alpha?=?0.004). In Experiment 2, we attempted to determine the relative gains in efficiency when using drift fences in conjunction with Longworth and pitfall traps. However, due to small sample size, we were unable to detect significant differences. A trapping protocol using Longworth traps in conjunction with drift fences, provided with mealworms as food, and checked at a maximum interval of 8 h should be sufficient to effectively include shrews in rodent livetrapping studies.     

Who’s in the hood? Assessing a novel rodent deterrent at pest fencing in New Zealand

ABSTRACT

Fenced ecosanctuaries may reduce predator presence at reserves by incorporating deterrents into pest management programmes. We quantified rodent visits to the steel hood of ecosanctuary fencing and illuminated our experimental sites to assess whether light could deter ship rats (Rattus rattus) and house mice (Mus musculus). Additionally, we assessed how mice used fencing in the presence and absence of ship rats by utilising two types of fence sections: one accessible to mice alone (along fencing within an ecosanctuary) and one accessible to mice and rats (at perimeter fence sites opposite pasture or forest habitat). We monitored sites using cameras and tracking cards within the fence hood and at tunnels at the fence base. Along the internal fence, mice were never observed within the hood but marked 40% of tunnels at the fence base. Along the perimeter fence, mice made four visits to the hood and marked 28% of tunnels at the fence base. Rats travelled exclusively within the fence hood (n?=?42). Light did not reduce rat sightings but adjacent habitat affected their presence (forest > pasture; p?≤?0.01). Positioning future ecosanctuary fencing alongside pasture and maintaining open corridors opposite fences at current ecosanctuaries may reduce rat presence.     

Earthen Structures Built by Ilyoplax dentimerosa (Crustacea,Brachyura, Ocypodidae)

Under observation, the small ocypodid crab Ilyoplax dentimerosa was found to commonly build three types of earthen structures: a barricade near its neighbour's burrow, a fence at an intermediate position between the burrows of the builder and its neighbour, and a minishelter near the builder's burrow. The sex ratio of barricade builders was found to be close to 1:1, whereas most of the fence builders were found to be female. Crabs against which barricades and fences were built, were usually smaller than the builders. Both barricade builders and fence builders had, in most cases, minishelters at the side, facing the barricade or the fence. Removal and rebuilding experiments for barricades and fences demonstrated that both structures functioned to deter the approach of the builder's neighbour to the builder's activity site. Fences also had the effect of restraining the movement of the builder toward the fence site.     

The relationship of body size to survivorship of hatchling snapping turtles (Chelydra serpentina): an evaluation of the “bigger is better” hypothesis

In many organisms, body size is positively correlated with traits that are presumably related to fitness. If directional selection frequently favors larger offspring (the “bigger is better” hypothesis), the results of such selection should be detectable with field experiments. We tested the “bigger is better” hypothesis in hatchling snapping turtles (Chelydra serpentina) by conducting one long-term and three short-term experiments on the University of Michigan E.S. George Reserve in southeastern Michigan. In the fall of 1995 and 1996, we released hatchlings at artificial nests separated from the nearest wetland by fences. We recorded the proportion of hatchlings recaptured, the time it took hatchlings to move to fences from artificial nests 45, 55, and 80 m away, and dispersion along the fence. We determined whether the response variables and probability of recapture at fences were associated with hatchling body size. During 1995, average travel times of hatchlings from the experimental nests were not related to distance from the fence; however, time to recapture was positively correlated with dispersion from the zero point on the fence, and the maximum time to reach the fence was almost twice as long for hatchlings from the 80-m nest compared to those from the 45-m nest. Sixty-seven percent of the hatchlings reached the fence and the proportions doing so from each nest were not different. Body size was not significantly related to probability of recapture in either of the 1995 experiments. In 1996, 59% of released hatchlings were recaptured. Time to recapture was not related to dispersion from the zero point or to body size. Cubic spline analysis suggested stabilizing selection on body size. We also conducted a set of long-term hatchling release experiments between 1980–1993 to compare the survival of hatchlings released at nest sites to that of hatchlings released directly into marshes, and we looked for relationships between survivorship and hatchling body size. During 7 years in which more than 30 hatchlings were released, 413 hatchlings were released directly into the marsh and 262 were released at nests: their probability of survival did not differ. Over all years, for both release groups combined and for each group separately, survival was not related to body size. In 1983 alone, survival was also not related to body size for either group or for both groups combined. In our three short-term experiments and one long-term experiment, we found no evidence to support the “bigger is better” hypothesis. When selection on body size did occur, selection was stabilizing, not directional for larger size. Received: 4 June 1998 / Accepted: 24 June 1999     

DISPERSAL BY YEARLING MALE WHITE-TAILED DEER AND IMPLICATIONS FOR MANAGEMENT

Abstract: The scale at which populations use the landscape influences ecological processes and management decisions. Dispersal and home-range size define the scale of landscape use for many large-mammal species. We measured dispersal and home-range size of yearling male white-tailed deer (Odocoileus virginianus) in southern Texas, and compared our results to values from the literature to understand the implications of dispersal in management of deer populations. We used radiotelemetry to monitor 22 yearling deer on 1 study site from October 1998 to October 1999, and 27 yearling deer on a second study site from October 1999 to October 2000. On the 2 study sites, 68% and 44% of yearling deer established new areas of use 4.4 ± 1.0 km and 8.2 ± 4.3 km, respectively, from the center of their autumn home range. Yearling males with spike antlers (2 points) were less likely to disperse than yearlings with fork antlers (>2 points) on 1 study site. Computer simulation showed that the scale at which deer use the landscape is large compared to property sizes in southern Texas and probably in other areas of the white-tailed deer's range. Differences in scale between land ownership patterns and landscape use by deer may result in a failure to meet management objectives and conflict among managers. High harvest rates for male deer occur in part because deer movements are large relative to property size, creating a “tragedy of the commons.” Cooperative management groups are beneficial if all landowners in an area agree on management objectives. Otherwise, deer-proof fences often are erected to reduce conflicts among property owners.     

Fence effects on the behavioural responses of South American fur seals to tourist approaches

Animals that breed in coastal colonies, such as pinnipeds, usually attract tourism, which can negatively affect their resting and breeding behaviour if not managed properly. One strategy to reduce human disturbance is to set up fences, but little is known about their local effectiveness. Our purpose was to assess the behavioural responses of South American fur seals (Arctocephaalus australis) towards tourist approaches before and after the implementation of fences in Cabo Polonio colony (Uruguay). We found that human disturbance levels were similar between years and that the presence of a fence reduced (1) overall fur seal responses to tourists by 60%, (2) the most intense behavioural responses (threat, attack, leaving the colony) by more than half, (3) the responses to large tourist groups (>2 people), which were the most disturbing, (4) the responses to closer (<10 m) tourist approaches, and (5) the responses involving more intrusive tourist behaviours (running, shouting, hand waving). Overall, we showed that after the erection of the fence not only human–wildlife interactions were reduced but also the most stressful fur seal behavioural responses. Although further studies are necessary, our results suggest that the implementation of fences can be a simple and affordable means of minimising human disturbance effects on pinnipeds at local levels (e.g., within colonies), particularly if combined with other strategies (e.g., changes in tourist attitudes).     

Undermining game fences: who is digging holes in Kalahari sands?

The effectiveness of game fencing as a tool to promote coexistence between humans and wildlife is highly dependent on the maintenance of fences. It is vital to identify animal species, which dig holes under fences, and their digging behaviour to maintain game fences appropriately. We provide data on some of southern Africa's major hole‐digging animal species for a simple albeit effective method enabling stakeholders to categorize species that are digging holes underneath game fences in deep sand habitats by species‐specific knowledge on sizes and shapes of holes. Using Botswana's Khutse Game Reserve/Central Kalahari Game Reserve fence as an example, we highlight the temporal aspect in the process of hole digging and enlargement. We present a method to determine the pressure a fence experiences by a number of hole‐digging species. Furthermore, we provide data on the time frame of necessary maintenance actions, required to prevent large predators from transgressing this specific fence line. We were especially interested in the effectiveness of fences in excluding African lions from human‐dominated areas. The predators proved to be very difficult to fence in and extremely opportunistic. They mostly utilized holes that were initially excavated by other, even very small species.     

Guanaco (Lama guanicoe) mortality by entanglement in wire fences

Wire fences are widely used in rangelands around the world and may have a negative impact on wildlife that varies among species and habitats. The guanaco (Lama guanicoe) is the largest Patagonian ungulate and though entanglement in wire fences is frequently reported, its impact on guanaco populations has not been previously evaluated. We estimated annual mortality rate of wild guanacos due to entanglement in wire fences and evaluated whether the frequency of entanglement was age-dependent in the two wire-fence designs traditionally used in Patagonian sheep ranches. We found that annual yearling mortality on fences (5.53%) was higher than adult mortality (0.84%) and was more frequent in ovine (93 cm high) than bovine (113 cm) fences. Most guanacos died entangled by their legs in the highest wire when trying to jump over the fence. Our results suggest that guanacos are more likely to die due to fence entanglement than ungulates studied in other regions. Indirect effects of wire fences should also be considered as they may act as semi-permeable barriers for guanaco populations. We suggest removal of unnecessary wire fences and replacement by guanaco-friendly fences, like high-tensile electric fences that may reduce mortality and barrier-effect on guanaco populations.     

The horizontal and vertical distribution of flying insects near artificial windbreaks

Lath fences 3 ft and 8 ft high affected the horizontal distribution of flying insects similarly: most insects accumulated at a distance equal to 2–3 times the height of each fence to leeward, where catches, measured at 14 and 38 in. (≡ to 0·4 times the height of the fence above the ground) were 30–40 % greater than in exposed positions. Behind an 8 ft fence accumulations extended vertically to 12–16 ft (≡ to 1·5-2·0 times the height of the fence). Vertical profiles of weak-flying insects, in winds > 3 m.p.h. differed in sheltered and exposed positions; in shelter the boundary layer was deeper and insects were more abundant nearer the ground than elsewhere. For strong flyers, and insects which flew only in winds < 2 m.p.h., vertical profiles in sheltered and exposed positions were indistinguishable.