Fenced Sections Research Articles

EMPTY CONTAINERS, OVERFLOWING RIVERS: STATE FUNDED FENCING AND IMPACTS IN EAGLE PASS, TEXAS

Abstract This study uses hydraulic modeling to examine the impacts of two new fence sections at Eagle Pass, Texas: a container fence and a state-funded fence section south, and downstream, of the already modeled federal border fence. We used the model Nays2DFlood to compare fence and non-fence conditions at various recurrence intervals to determine how the fence is affecting flood extents, water depth, and water velocity. Water depth is deeper in the channel and the floodplain and shallower directly at the fence line when compared to non-fence conditions. Water velocity is faster within the channel and the floodplain and slower at the fence line during fence conditions. These impacts have the potential to adjust sediment regimes at this location and downstream of this area, altering water quality and channel morphology. Demographic analysis also show that particularly susceptible populations, including a majority Latino, low income individuals, those under 5, and those 65–74, are present in large numbers at these fence sections and are therefore vulnerable to flooding. Supplemental material is available for this article online.

A before-after-control-impact study of wildlife fencing along a highway in the Canadian Rocky Mountains

Wildlife exclusion fencing has become a standard component of highway mitigation systems designed to reduce collisions with large mammals. Past work on the effectiveness of exclusion fencing has relied heavily on control–impact (i.e., space-for-time substitutions) and before–after study designs. These designs limit inference and may confound the effectiveness of mitigation with co-occurring process that also changes the rate of collisions. We used a replicated (n = 2 sites monitored for over 1000 km years combined) before-after-control-impact study design to assess fencing effectiveness along the Trans-Canada Highway in the Rocky Mountains of Canada. We found that collisions declined for common ungulates species (elk, mule deer, and white-tailed deer) by up to 96% but not for large carnivores. The weak response of carnivores is likely due to the combination of fence intrusions and low sample sizes. We calculated realized fencing effectiveness by applying the same change in collision rates observed at control (unfenced) sites as the expected change for adjacent fenced sections. Compared with the apparent fencing effectiveness (i.e., the difference in WVCs rates before and after fencing was installed), the realized estimates of fencing effectiveness declined by 6% at one site and increased by 10% at another site. When factoring in the cost of ungulate collisions to society, fencing provided a net economic gain within 1 year of construction. Over a 10-year period, fencing would provide a net economic gain of > $500,000 per km in reduced collisions. Our study highlights the benefits of long-term monitoring of road mitigation projects and provides evidence of fencing effectiveness for reducing wildlife–vehicle collisions involving large mammals.

Evaluating Responses by Sympatric Ungulates to Fence Modifications Across the Northern Great Plains

ABSTRACTAcross North America, incentive programs have assisted landholders with the construction of fences, often considered “wildlife friendly,” to assist in grazing management, which has resulted in a proliferation of fencing on the landscape. Many suggested “wildlife‐friendly” fence modifications have not been evaluated for their effectiveness on the targeted species or evaluated to assess consequences for nontarget species. We evaluated the effects of 2 modifications aimed to increase fence visibility (sage‐grouse [SAGR] reflectors and white polyvinyl chloride [PVC]) on the fence‐crossing behavior of 3 sympatric ungulates in the Northern Great Plains. We used trail cameras from 2016 to 2018 to capture images of pronghorn (Antilocapra americana), mule deer (Odocoileus hemionus), and white‐tailed deer (O. virginianus) at sites before and after fence sections were modified and compared crossing success by the 3 ungulates with that achieved at unchanged control sites. We used generalized linear modeling and a time‐to‐event approach to test the effect of fence modifications on ungulate crossing behavior. Our results showed that both SAGR reflectors and white PVC pipe did not impede fence‐crossing behaviors for either pronghorn or deer, nor was there a time lag in use of sites observed after modifications were deployed. Though we did not alter the height of the bottom wire, there was enough variability in bottom wire height between sites that our results indicate a greater probability of successful crossing by all 3 ungulates as bottom wire height increased. We recommend implementation of both SAGR reflectors and white PVC pipe because our results demonstrate no substantial unintended consequences on the crossing behavior of pronghorn and deer. © 2020 The Authors.Wildlife Society Bulletinpublished by Wiley Periodicals, Inc. on behalf of The Wildlife Society.

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.

How do landscape context and fences influence roadkill locations of small and medium-sized mammals?

Road mortality is the most easily visible effect of roads and traffic on wildlife populations. Mitigation measures such as fences and wildlife passages have been applied to reduce these effects. During the widening of Quebec's Highway 175 from two to four lanes between 2006 and 2012, 33 wildlife passages designed specifically for small and medium-sized mammals were installed under the road in combination with short fences. This study examined the effectiveness of the fences at reducing the number of small and medium-sized mammals killed along a 68 km section of the road while controlling for the potential confounding effects of landscape variables. Repeated daily mortality surveys were conducted by car during the summers of 2012–2015 to measure roadkill occurrence and detection probability. A total of 893 dead animals from 13 taxa were detected. Roadkill occurrence was significantly greater at fence ends than in fenced sections and unfenced sections (fence-end effect), indicating that the fences were not long enough to discourage animals from moving along the fence to the fence ends. Greater length would be required to meet the target of reduced road mortality. Shrubby vegetation in the median strip separating the two directions of the highway was associated with high roadkill occurrence for medium-sized species. Roadkill detection probability for all species combined was 0.72, ranging from 0.17 for small mammals (<1 kg) to 0.82 for medium-sized mammals (>1 kg). To reduce road mortality, when wildlife passages are constructed along with new highways or retrofitted to old highways, fences either should be continuous or sufficiently long to encourage passage use rather than movement around the fence ends. Future road mortality studies should be combined with data about wildlife abundance and detection probability to more accurately estimate the effects at the population level.

Do Crash Barriers and Fences Have an Impact on Wildlife–Vehicle Collisions?—An Artificial Intelligence and GIS-Based Analysis

Wildlife–vehicle collisions (WVCs) cause significant road mortality of wildlife and have led to the installation of protective measures along streets. Until now, it has been difficult to determine the impact of roadside infrastructure that might act as a barrier for animals. The main deficits are the lack of geodata for roadside infrastructure and georeferenced accidents recorded for a larger area. We analyzed 113 km of road network of the district Freyung-Grafenau, Germany, and 1571 WVCs, examining correlations between the appearance of WVCs, the presence or absence of roadside infrastructure, particularly crash barriers and fences, and the relevance of the blocking effect for individual species. To receive infrastructure data on a larger scale, we analyzed 5596 road inspection images with a neural network for barrier recognition and a GIS for a complete spatial inventory. This data was combined with the data of WVCs in GIS to evaluate the infrastructure’s impact on accidents. The results show that crash barriers have an effect on WVCs, as collisions are lower on roads with crash barriers. In particular, smaller animals have a lower collision share. The risk reduction at fenced sections could not be proven as fenced sections are only available at 3% of the analyzed roads. Thus, especially the fence dataset must be validated by a larger sample number. However, these preliminary results indicate that the combination of artificial intelligence and GIS may be used to analyze and better allocate protective barriers or to apply it in alternative measures, such as dynamic WVC risk-warning.

Класифікація мобільних живоплотів

Для тимчасового або довгострокового озеленення урбанізованих територій, на яких немає можливості створення традиційних елементів озеленення, доцільно створювати мобільні живоплоти із застосуванням новітніх технологій. Моделювання процесів планування, створення і формування мобільних живоплотів має базуватися на поєднанні декоративного, агротехнічного та екологічного принципів, що надалі забезпечуватиме еколого-біологічну стабільність живих огорож та їх стійкість до впливу несприятливих природних і антропогенних чинників урбанізованого середовища. Вперше висвітлено класифікацію мобільних живоплотів, яка поділяє їх на дві групи – прості та каркасні мобільні живоплоти; за видовим складом – чисті та змішані; за висотою – низькі, середні та високі. Також за тривалістю використання на одному об'єкті озеленення виділено тимчасові, сезонні, довгострокові мобільні живоплоти. Залежно від розмірів, ваги однієї секції, що безпосередньо впливає на мобільність цього елементу озеленення, за можливістю переміщення поділяють на: високомобільні, середньомобільні та маломобільні. Наведено рекомендації щодо видового складу, використання мобільних живоплотів. Доведено, що мобільні живоплоти є перспективними для використання їх у ландшафтному дизайні та озелененні територій.

One‐way gates successfully facilitate the movement of burrowing bettongs (Bettongia lesueur) through exclusion fences around reserve

AbstractWhen native herbivores are enclosed in fenced reserves without predators or dispersal options then overgrazing can occur, leading to damage to vegetation and co‐occurring fauna species. One‐way gates that allow medium‐sized herbivores to exit fenced reserves may be an effective management tool to address overabundance or facilitate population expansion. We tested the use of one‐way gates to facilitate the movement of the reintroduced burrowing bettong (Bettongia lesueur) from inside to outside a fenced reserve in arid South Australia. One‐way gates were installed in the exterior fence of the reserve and assessed using remote motion‐sensor cameras. The influence of gate position (dune, swale or corner) and provision of food were assessed in relation to gate visits and exits. Animals were trapped inside and outside the gates to determine any population bias in gate exits. Baited gates recorded significantly more exits than unbaited gates and dune gates had higher exit rates than interdunal swale gates. When gates were unbaited, those installed in corners of the reserve showed significantly higher visitation by bettongs and a non‐significant trend towards more exits compared to gates placed in straight sections of fence along dunes or swales. There was no sex or age bias of burrowing bettongs using the gates and bettongs travelled between 75 m and 1535 m from their warrens to use the gates. No non‐target species gained access to the reserve through the one‐way gates and only two non‐target animals used the gates to exit the reserve confirming gate specificity for bettongs. During the same period, 96 burrowing bettongs exited the reserve through the one‐way gates. One‐way gates may be a management strategy for facilitating passive movement of medium‐sized herbivores outside of fenced reserves for the purposes of reducing overpopulation or facilitating population expansion outside reserves.

A regional model of sheep lice management practices to examine the impact of managing straying sheep combined with other management choices

A model of lice management systems was used to investigate the potential benefits of improved fencing against straying sheep, used in conjunction with other management options for lice control. The impact of combined strategies was simulated over a 20-year period. Management options included in the model were: lice eradication rate, lice detection, intervention level, improved fencing to reduce straying sheep, and biosecurity of purchased sheep. The modelling found it was cost-effective to improve fences for an initial average cost of $20 000/property if the number of properties from which strays could enter was reduced by ≥40%, but for average Australian properties this represents less than 20% of the boundary replaced. In order for fencing to be a cost-effective part of lice management, the fencing must target sections of boundary fence that will provide the greatest protection from contact with neighbouring flocks. The model showed that improved biosecurity against straying sheep combined well with improved eradication rates. However, biosecurity for purchased sheep may be the most cost-effective option.

Effectiveness of short sections of wildlife fencing and crossing structures along highways in reducing wildlife–vehicle collisions and providing safe crossing opportunities for large mammals

Wildlife fencing in combination with crossing structures is commonly regarded as the most effective and robust strategy to reduce large mammal–vehicle collisions while also maintaining wildlife connectivity across roads. However, fencing and associated measures may affect landscape esthetics and are sometimes considered costly and unpopular. Therefore fence length is often minimized. We investigated 1) whether short fenced road sections were similarly effective in reducing large mammal–vehicle collisions as long fenced road sections (literature review), and 2) whether fence length influenced large mammal use of underpasses (two field studies). We found that: 1) short fences (≤5km road length) had lower (52.7%) and more variable (0–94%) effectiveness in reducing collisions than long fences (>5km) (typically >80% reduction); 2) wildlife use of underpasses was highly variable, regardless of fence length (first field study); 3) most highway crossings occurred through isolated underpasses (82%) rather than at grade at fence ends (18%) (second field study); and 4) the proportional use of isolated underpasses (compared to crossings at fence ends) did not increase with longer fence lengths (up to 256m from underpasses) (second field study). If the primary success parameter is to improve highway safety for humans by reducing collisions with large ungulates, the data suggest fence lengths of at least 5km. While longer fence lengths do not necessarily guarantee higher wildlife use of underpasses as use varies greatly between locations, wildlife fencing can still improve wildlife use of an individual underpass.

Ignition of Wood Fencing Assemblies Exposed to Continuous Wind-Driven Firebrand Showers

Post-fire studies conducted by NIST on the Waldo Canyon Fire in Colorado (2012) determined that wood fencing assemblies are believed to be vulnerable to ignition from firebrand showers in Wildland–Urban Interface fires, but again there has never been any experimental verification of this ignition mechanism. As a result, a series of experiments were conducted to examine ignition of wood fencing assemblies subjected to continuous, wind-driven firebrand showers. Western Red Cedar and Redwood fencing assemblies were exposed to continuous, wind-driven firebrands generated by the NIST full-scale Continuous Feed Firebrand Generator installed in the Fire Research Wind Tunnel Facility at the Building Research Institute in Japan. To simulate fine fuels that may be present near fencing assemblies, dried shredded hardwood mulch beds were placed adjacent to the fencing assemblies. The fencing assemblies were varied in length and in orientation to the applied wind field to simulate a range of configurations that may be encountered in realistic situations. Both flat and corner sections of fencing assemblies were used in these experiments. The dimensions of the flat wood fencing assemblies sections were varied from 0.91 m wide, 1.83 m in height to 1.83 m wide, 1.83 m in height. With respect to the corner sections, the dimensions used were 0.91 m by 0.91 m by 1.83 m in height. All configurations considered resulted in flaming ignition (FI) of the mulch beds, and subsequent FI of the wood fencing assemblies. Finally, experiments were also completed to determine if wind-driven firebrand showers could produce FI of fencing assemblies without the presence of fine fuels adjacent to the fence sections. Firebrands produced smoldering ignition (SI) of the fencing assemblies without fine fuels present, and SI transitioned to FI under the applied wind field. These experiments have demonstrated that wood fencing assemblies are vulnerable to ignition by wind-driven firebrand showers.

Temporal shifts in activity of prey following large predator reintroductions

The response of prey to predation risk varies through time and space. These responses relate to trade-offs between foraging and predator avoidance. Following the extirpation of predators from many landscapes, the responses related to predator avoidance may have been lost or diluted. Investigating the activity pattern of prey species on comparable landscapes with and without large predators provides an opportunity to understand how predators may shape prey activity and behaviour. Using camera trap data from neighbouring fenced sections of the Addo Elephant National Park (Eastern Cape, South Africa), we investigated the activity patterns of species exposed to large predators, where the predators were only present in one of the sections. Our results suggest that prey species at risk of predation (e.g., buffalo, kudu and warthog) are more likely to be active diurnally when co-existing with nocturnally active predators, thereby reducing the activity overlap with these predators. In the absence of predators, kudu and buffalo were more active at night resulting in a low overlap in activity between sections. Warthog activity was predominantly diurnal in both sections, resulting in a high overlap in activity between sections. The presence of predators reduced the nocturnal activity of warthogs from 6 to 0.6 % of all warthog captures in each section. Elephants, which are above the preferred prey weight range of the predators and therefore have a low risk of predation, showed higher overlap in activity periodicity between predator-present and predator-absent areas. Our findings suggest that maintaining prey with their predators has the added benefit of conserving the full spectrum of prey adaptive behaviours.

Effectiveness of wildlife guards at access roads

The reconstruction of 90.6 km of U.S. Highway 93 from Evaro to Polson, Montana, USA, includes 41 wildlife crossing structures and 13.4 km of road with wildlife fencing. These measures are aimed at reducing wildlife–vehicle collisions and increasing human safety, while allowing wildlife to traverse the landscape. In the fenced road sections, gaps in the fence for side roads are mitigated by wildlife guards (similar to cattle guards). We monitored wildlife movements with cameras for 2 years from mid-July 2008 to mid-July 2010 at 2 wildlife guards and in 1 large crossing structure adjacent to one of the wildlife guards. We investigated how effective these wildlife guards were as a barrier to deer (Odocoileus spp.), black bear (Ursus americanus), and coyotes (Canis latrans). We also compared movements across a wildlife guard with movements through an adjacent crossing structure. The wildlife guards were ≥85% effective in keeping deer from accessing the road and 93.5% of deer used the crossing structure instead of the adjacent wildlife guard when crossing the road. The wildlife guards were less effective in keeping black bear and coyotes from accessing the road (33–55%). However, all black bears and 94.7% of coyotes used the crossing structure instead of the adjacent wildlife guard when crossing the road. Though the wildlife guards were not an absolute barrier to these species, the results indicate wildlife guards are a substantial barrier to deer and can be considered effective in mitigating gaps in a fence at access roads for these species. © 2013 The Wildlife Society.

Are invasive and native trout functionally equivalent predators? Results and lessons from a field experiment

Non-native brook trout (Salvelinus fontinalis) have replaced native cutthroat trout (Oncorhynchus clarkii) in streams across the western USA. Brook trout have been assumed to be functionally equivalent to cutthroat trout, which could argue against extensive control of this species by government agencies. This assumption was assessed by comparing the diets of the two trout species and their effects on benthic invertebrates in a large-scale field experiment. Within a Rocky Mountain stream where brook trout had already become established, trout species and density were manipulated in 20 fenced sections to create four treatments: cutthroat trout at a density natural for un-invaded streams, brook trout at two densities, natural for invaded streams or reduced to match the natural density of cutthroat trout, and areas depleted of most trout. By the end of the experiment, populations of brook trout at natural density consumed seven times more benthic invertebrates than cutthroat trout. Brook trout also consumed more Apatania caddisflies and Heterlimnius riffle beetles per capita than cutthroat trout. However, the greater consumption did not cause detectable reductions in benthic invertebrate densities. A large-scale experiment of trout removal like this may be inherently limited in its ability to detect effects on benthic invertebrate densities. However, this and several companion studies indicate that stream ecosystems would not function in the same way if cutthroat trout are replaced by brook trout. Sustaining these functions, as well as biodiversity and socioeconomic values, are important reasons to conserve native cutthroat trout. Copyright © 2012 John Wiley & Sons, Ltd.

TURTLE ENERGY EXPENDITURE FROM ACCELERATION

Gliding through the warm south-western Indian Ocean, green turtles live a peaceful life feasting on seagrass meadows before returning to their deep coral reef homes. But their idyllic lifestyle is under threat from human activity; so understanding how these enigmatic creatures stay in tune with their environment is becoming increasingly important. ‘If they don't balance their energy budget there is going to be a problem for the individual and later on at a population level,’ explains Manfred Enstipp from the DEPE/CNRS Laboratory in Strasbourg, France. However, conventional methods for measuring energy expenditure may be unreliable in turtles, so Enstipp and Jean-Yves Georges decided to try another approach: measuring the animals' movements with accelerometers to estimate their energy use. First, the team had to discover whether there was a measurable relationship between the turtle's acceleration and their oxygen consumption in order to extrapolate the animals' energy use from their activity (p. 4010).However, when Enstipp and his colleagues embarked on the study they weren't even sure that they could measure the turtle's oxygen consumption rate. ‘They had to find this hole that is 40×40 cm to breathe so that we could measure the oxygen consumption rate,’ explains Enstipp, but many of his colleagues thought that the freely swimming animals could not be trained to surface repeatedly at a single point in long channel.Travelling to Stephane Ciccione's Kelonia Turtle Aquarium on Reunion Island, Enstipp isolated a 13 m-long swim channel in the turtles' enclosure and then, over a period of months, he and Benoit Gineste slowly covered the channel's surface with sections of metal fence until the turtles were content to surface and breathe at the respirometry dome, which covered the channel's only remaining open surface. Despite his colleagues' misgivings, Enstipp found that the turtles successfully learned to surface and breathe at the respirometry dome. Then, Enstipp velcroed a two-axis accelerometer onto a turtle's shell before recording her oxygen consumption and movements as she swam to and fro.Returning to Reunion Island with Gineste, Myriam Milbergue and Virginie Plot in the summer and winter, Enstipp successfully measured the oxygen consumption rates of six adult turtles at temperatures ranging from 24.8 to 30.1°C while also measuring their acceleration patterns. But could he use the acceleration traces to accurately estimate the turtles' oxygen consumption?Developing an equation to calculate the turtles' oxygen consumption based on their acceleration and the temperature of the surrounding water – which determines turtle metabolic rate – Enstipp calculated the turtles' oxygen consumption rates and compared them with the animals' measured oxygen consumption rates. They agreed well: the team could use the turtle's acceleration pattern to calculate their oxygen consumption, which they could use as a proxy for the animal's energy consumption.But how does the captive turtle's activity level compare with that of free-ranging green turtles grazing their seagrass meadows? ‘We are trying to apply this to Katia Ballorain's data from turtles foraging around Mayotte Island,’ Enstipp reports. However, early evidence suggests that the captive turtles were no couch potatoes and were every bit as active as their free-ranging cousins, offering Enstipp and his colleagues hope that accelerometery could provide much needed measurements of green turtles' energy consumption in the wild.

A questionnaire-based evaluation of the veterinary cordon fence separating wildlife and livestock along the boundary of the Kruger National Park, South Africa

Veterinary cordon fences are used in Southern Africa to separate wildlife from domestic animals in order to prevent transmission of infectious diseases. Such fences are a control method recognized by the World Organization for Animal Health (OIE) for establishing disease-free zones in beef exporting countries. However, few studies have evaluated the ecological impact of these physical barriers or their effectiveness at a multispecies level. We examined the permeability of one such barrier, along 357 km of the western and southern boundary of the Kruger National Park (KNP) during 2007. Information was gathered using a semi-structured questionnaire implemented among 32 teams of fence maintenance workers. Data were analyzed to identify (a) the main causes of fence damage, (b) the seasonality, location and duration of fence repairs, (c) high permeability areas for elephant ( Loxodonta africana), kudu ( Tragelaphus strepsiceros), impala ( Aepyceros melampus), buffalo ( Syncerus caffer) and warthog ( Phacochoerus africanus), and (d) the influence of fence electrification, rivers and elephant damage on the frequency of observation of wildlife species outside the KNP estimated during the year. Human and elephant damage were the most common reasons for fence repairs. Elephant and buffalo were the most and least common large mammal species reported observed outside the KNP (1076 and 162 reports/year), respectively. Cattle incursions into the KNP were also reported in 44% of the fence sections. Electrification of the fence was an important factor explaining differences in estimated wildlife species observations outside the KNP during the year. Correlations between estimations of observed species suggested that fence gaps created by elephants might be used by the other wildlife species. Estimated annual counts of kudu, impala and buffalo, but not warthog, were found to correlate with elephant observations. Negative binomial regression models were developed to explore the relationships between observed estimations of different wildlife species outside the KNP the fence, electrification of fence sections and the presence of watercourses, suggesting that kudu, impala and buffalo could use elephant induced fence damage to leave the KNP. The questionnaire was able to evaluate fence integrity and identify sections where integrity was sub-optimal for separating wildlife from domestic livestock species. If combined with more quantitative methods and applied on a routine basis, it could provide an efficient and cost-effective method for monitoring the effectiveness of physical barriers to contain wildlife within protected areas such as is the case with veterinary cordon fences in Southern Africa.

Effects of a highway and mitigation projects on bobcats in Southern Texas

Roads are a common landscape feature that may negatively impact wildlife. These impacts may be reduced by altering roads and their right-of-ways. We studied impacts of a 4-lane divided highway on bobcats ( Lynx rufus) in southern Texas. From June 1997 to May 1999, 25 bobcats were found dead on the 32.2 km section of highway we studied. Mortalities were more likely adjacent to habitat preferred by bobcats and in sections of the highway in which thornshrub had been left in the median. Bobcats used culverts to cross under the highway and for other activities, such as resting. Culvert use was positively related to the openness ratio (width×height/length) of the culvert and to the amount of thornshrub cover adjacent to the culvert. Sections of fence 100 m long erected to funnel wildlife toward culverts did not increase bobcat use of culverts in an analysis of all culverts, but may have increased use of high-use culverts. Our results highlight the competing nature of techniques to minimize population fragmentation and mortality. Projects to reduce the impact of roads on wildlife should consider which impacts are likely to be most detrimental and ensure that efforts to mitigate one impact will not increase another.

Ecological influences on transmission rates of Ascaris suum to pigs on pastures

A study was conducted to determine the distribution and transmission rate of Ascaris suum eggs and Oesophagostomum dentatum larvae in a pasture/pig house facility, which during the preceding summer was contaminated with helminth eggs by infected pigs. In May, four groups of 10 helminth naı̈ve tracer pigs were exposed to fenced sections of the facility for 7 days and necropsied for parasite recovery 9–10 days later (trial 1). The highest rate of A. suum transmission (201 eggs per day) occurred in the pig house (A). On the pasture, egg transmission decreased with the distance from the house: 8 eggs per day in the feeding/dunging area (B); 1 egg per day on the nearest pasture (C); <1 egg per day on the distant pasture (D). Only a few O. dentatum infections were detected, indicating a poor ability of the infective larvae to overwinter. Soil analyses revealed that the highest percentage (5.8%) of embryonated A. suum eggs were in the house (A). Subsequently, the facility was recontaminated with A. suum eggs by infected pigs. A replicate trial 2 was conducted in the following May. A major finding was the complete reversal of egg distribution between the 2 years (trials 1 and 2). In contrast to previous results, the highest rates of transmission (569 and 480 eggs per day) occurred in pasture sections C and D, and the lowest transmission rates (192 and 64 eggs per day) were associated with the feeding/dunging sections and the house (B and A). Soil analyses again supported the tracer pig results, as the pasture sections had the highest concentrations of embryonated eggs. Detailed soil analysis also revealed a non-random, aggregated egg distribution pattern. The different results of the two trials may be due to the seasonal timing of egg deposition and tracer pig exposure. Many eggs deposited during the summer prior to trial 1 may have died rapidly due to high temperatures and dessication, especially when they were not protected by the house, while deposition in the autumn may have favored egg survival through lower temperatures, more moisture, and greater sequestration of eggs in the soil by rain and earthworms. The latter eggs may, however, not have become embryonated until turnout the next year. The results demonstrate that yearly rotations may not be sufficient in the control of parasites with long-lived eggs, such as A. suum, and that a pasture rotation scheme must include all areas, including housing.

Reindeer Rangifer tarandus fences as a mortality factor for ptarmigan Lagopus spp.

To assess how important reindeer Rangifer tarandus fences are as a mortality factor for ptarmigan Lagopus spp. we collected data during 1991–1994. Our fieldwork covered 12 different sections of reindeer fence (totalling 71.1 km) in the county of Finnmark, northern Norway. The sections consisted of steel wire, steel netting or a combination of these, and ranged in height from 100 to 250 cm. The fieldwork took the form of spring patrols during which dead birds and their remains were searched for along the fences immediately after snow melt. We covered a total of 179.9 km and found 253 collision victims belonging to at least 20 species. Of the 253 victims found, 215 were willow ptarmigan Lagopus lagopus and rock ptarmigan L. mutus; thus these two species comprised 85% of the victims. During the winters of 1992/93 and 1993/94, we carried out experiments with dummy willow ptarmigan which were placed along fence sections and monitored serving as artificial fencestrike victims. Our experiments showed that approximately 64% of the total number of ptarmigan killed by the fences during winter would be detected during spring patrols along the fences. The type and height of the fence had no effect on the ptarmigan collision rate. In contrast, both the fence section and year factor contributed significantly to the observed variation in collision rate. We estimate that on average 1.4 ± 0.5 (SE) ptarmigan are being killed per kilometre of reindeer fence in Finnmark annually, with a greater variation between fence sections than between years.

Influences of Predatory Fish on the Drift Dispersal and Local Density of Stream Insects

Researchers have recently suggested that frequent prey dispersal into and out of an area can swamp the local effect on predation. Where prey are mobile, the extent of prey movement can therefore explain variation in the apparent effect of predators on local prey density. I compared the effect of the dominant predator in a temperate stream (brook charr, Salvelinus fontinalis Mitchill) on five insect prey taxa (mayflies: Ephemeroptera), to test the prediction that the extinct of density reduction should be less for prey taxa dispersing more frequently. The propensity of the mayflies to disperse by drifting downstream in the water column was measured in unmanipulated areas of the stream. Relative propensity to drift of the five mayflies was, from greatest to least: Baetis, Paraleptophlebia, Ephemerella, Eurylophella, Stenonema. I then tested effects of charr on the mayflies by manipulating charr density in fenced 35—m sections of the stream. Charr densities were adjusted to zero, medium, and high levels relative to natural densities. Rates of predation by charr in stream sections did not vary among the five mayfly taxa. Charr caused a large reduction in the density of Baetis, had a smaller effect on Paraleptophlebia, but had no detectable effect on the density of the other mayflies. Drift dispersal into the stream sections did not differ among charr densities. Effects of charr on prey densities could thus have been caused by direct predation or by increases in emigration from areas containing charr. Charr caused increased drift dispersal of Baetis and of Paraleptophlebia, but had no influence on drift of the other three mayflies. The reduction in density of Baetis by charr was due more to the charr—induced increase in drifting of Baetis than to direct predation on Baetis. The hypothesis that frequent prey dispersal swamps the effects of predators assumes that predators influence prey density primarily by consuming prey. In this system charr also influenced prey densities by causing increases in prey drift rates, affecting the mayflies that drifted most frequently. For this reason, the mayflies drifting less frequently were not, as predicted, the ones most strongly affected by charr. Variation in the effect of predators on prey density may thus be partially explained by both (1) changes in prey dispersal not related to predators, as proposed in the initial hypothesis, and (2) influences of predators on prey dispersal.