Anthony P. Clevenger

Effects of Road Networks on Bird Populations

One potential contributor to the worldwide decline of bird populations is the increasing prevalence of roads, which have several negative effects on birds and other vertebrates. We synthesized the results of studies and reviews that explore the effects of roads on birds with an emphasis on paved roads. The well-known direct effects of roads on birds include habitat loss and fragmentation, vehicle-caused mortality, pollution, and poisoning. Nevertheless, indirect effects may exert a greater influence on bird populations. These effects include noise, artificial light, barriers to movement, and edges associated with roads. Moreover, indirect and direct effects may act synergistically to cause decreases in population density and species richness. Of the many effects of roads, it appears that road mortality and traffic noise may have the most substantial effects on birds relative to other effects and taxonomic groups. Potential measures for mitigating the detrimental effects of roads include noise-reduction strategies and changes to roadway lighting and vegetation and traffic flow. Road networks and traffic volumes are projected to increase in many countries around the world. Increasing habitat loss and fragmentation and predicted species distribution shifts due to climate change are likely to compound the overall effects of roads on birds.

An Assessment of Road Impacts on Wildlife Populations in U.S. National Parks

Current United States National Park Service (NPS) management is challenged to balance visitor use with the environmental and social consequences of automobile use. Wildlife populations in national parks are increasingly vulnerable to road impacts. Other than isolated reports on the incidence of road-related mortality, there is little knowledge of how roads might affect wildlife populations throughout the national park system. Researchers at the Western Transportation Institute synthesized information obtained from a system-wide survey of resource managers to assess the magnitude of their concerns on the impacts of roads on park wildlife. The results characterize current conditions and help identify wildlife-transportation conflicts. A total of 196 national park management units (NPS units) were contacted and 106 responded to our questionnaire. Park resource managers responded that over half of the NPS units’ existing transportation systems were at or above capacity, with traffic volumes currently high or very high in one quarter of them and traffic expected to increase in the majority of units. Data is not generally collected systematically on road-related mortality to wildlife, yet nearly half of the respondents believed road-caused mortality significantly affected wildlife populations. Over one-half believed habitat fragmentation was affecting wildlife populations. Despite these expressed concerns, only 36% of the NPS units used some form of mitigation method to reduce road impacts on wildlife. Nearly half of the respondents expect that these impacts would only worsen in the next five years. Our results underscore the importance for a more systematic approach to address wildlife-roadway conflicts for a situation that is expected to increase in the next five to ten years.

Genetic connectivity for two bear species at wildlife crossing structures in Banff National Park

Roads can fragment and isolate wildlife populations, which will eventually decrease genetic diversity within populations. Wildlife crossing structures may counteract these impacts, but most crossings are relatively new, and there is little evidence that they facilitate gene flow. We conducted a three-year research project in Banff National Park, Alberta, to evaluate the effectiveness of wildlife crossings to provide genetic connectivity. Our main objective was to determine how the Trans-Canada Highway and crossing structures along it affect gene flow in grizzly (Ursus arctos) and black bears (Ursus americanus). We compared genetic data generated from wildlife crossings with data collected from greater bear populations. We detected a genetic discontinuity at the highway in grizzly bears but not in black bears. We assigned grizzly bears that used crossings to populations north and south of the highway, providing evidence of bidirectional gene flow and genetic admixture. Parentage tests showed that 47% of black bears and 27% of grizzly bears that used crossings successfully bred, including multiple males and females of both species. Differentiating between dispersal and gene flow is difficult, but we documented gene flow by showing migration, reproduction and genetic admixture. We conclude that wildlife crossings allow sufficient gene flow to prevent genetic isolation.

Comparison of Methods of Monitoring Wildlife Crossing-Structures on Highways

Abstract Wildlife crossing-structures (e.g., underpasses and overpasses) are used to mitigate deleterious effects of highways on wildlife populations. Evaluating performance of mitigation measures depends on monitoring structures for wildlife use. We analyzed efficacy of 2 noninvasive methods commonly used to monitor crossing-structure use by large mammals: tracking and motion-activated cameras. We monitored 15 crossing-structures every other day between 29 June and 24 October 2007 along the Trans-Canada Highway in Alberta, Canada. Our objectives were to determine how species-specific detection rates are biased by the detection method used, to determine factors contributing to crossing-event detection, and to evaluate the most cost-effective approach to monitoring. We detected 3,405 crossing events by tracks and 4,430 crossings events by camera for mammals coyote-sized and larger. Coyotes (Canis latrans) and grizzly bears (Ursus arctos) were significantly more likely to be detected by track-pads, whereas elk (Cervus elaphus) and deer (Odocoileus sp.) were more likely to be detected by cameras. Crossing-event detection was affected by species, track-pad length, and number of animals using the crossing structure. At the levels of animal activity observed in our study our economic analysis indicates that cameras are more cost-effective than track-pads for study durations >1 year. Understanding the benefits and limitations of camera and track-pad methods for monitoring large mammal movement at wildlife crossing-structures will help improve the efficiency of studies designed to evaluate the effectiveness of highway mitigation measures.

Estimating Grizzly and Black Bear Population Abundance and Trend in Banff National Park Using Noninvasive Genetic Sampling

We evaluated the potential of two noninvasive genetic sampling methods, hair traps and bear rub surveys, to estimate population abundance and trend of grizzly (Ursus arctos) and black bear (U. americanus) populations in Banff National Park, Alberta, Canada. Using Huggins closed population mark-recapture models, we obtained the first precise abundance estimates for grizzly bears ( = 73.5, 95% CI = 64–94 in 2006;  = 50.4, 95% CI = 49–59 in 2008) and black bears ( = 62.6, 95% CI = 51–89 in 2006;  = 81.8, 95% CI = 72–102 in 2008) in the Bow Valley. Hair traps had high detection rates for female grizzlies, and male and female black bears, but extremely low detection rates for male grizzlies. Conversely, bear rubs had high detection rates for male and female grizzlies, but low rates for black bears. We estimated realized population growth rates, lambda, for grizzly bear males ( = 0.93, 95% CI = 0.74–1.17) and females ( = 0.90, 95% CI = 0.67–1.20) using Pradel open population models with three years of bear rub data. Lambda estimates are supported by abundance estimates from combined hair trap/bear rub closed population models and are consistent with a system that is likely driven by high levels of human-caused mortality. Our results suggest that bear rub surveys would provide an efficient and powerful means to inventory and monitor grizzly bear populations in the Central Canadian Rocky Mountains.

Connectivity Conservation: Maintaining and restoring connectivity in landscapes fragmented by roads

INTRODUCTION Transportation networks and systems are vital to todays economy and society (Button and Hensher 2001). Not only do roads provide for safe and efficient movement of goods and people across cities and continents, throughout the world they have become a permanent part of our physical, cultural, and social environment (Robinson 1971; Lay 1992). Roads and their networks are one of the most prominent human-made features on the landscape today (Sanderson et al . 2002). Compared to polygonal blocks of built areas, road systems are linear and etched into the landscape to form a woven network of arteries that maintain the pulse of societies. However, as road networks extend across the landscape and their weave intensifies, natural areas become increasingly fragmented and impoverished biologically (Forman et al . 2003). Although less studied compared to other agents of fragmentation, roads cause changes to wildlife habitat that are more extreme and permanent than other anthropogenic sources of fragmentation (Forman and Alexander 1998; Spellerberg 2002). Road networks and systems not only cause conspicuous changes to physical landscapes, but also alter the patterns of wildlife and the general function of ecosystems within these landscapes (Swanson et al . 1988; Transportation Research Board 1997; Olander et al . 1998). Busy roads can be barriers or filters to animal movement (Hels and Buchwald 2001; Rondinini and Doncaster 2002; Chruszcz et al . 2003) and in some cases the leading cause of animal mortality (Maehr et al . 1991; Jones 2000; Kaczensky et al . 2003).

Demographic Connectivity for Ursid Populations at Wildlife Crossing Structures in Banff National Park

Wildlife crossing structures are one solution to mitigating the fragmentation of wildlife populations caused by roads, but their effectiveness in providing connectivity has only been superficially evaluated. Hundreds of grizzly (Ursus arctos) and black bear (Ursus americanus) passages through under and overpasses have been recorded in Banff National Park, Alberta, Canada. However, the ability of crossing structures to allow individual and population-level movements across road networks remains unknown. In April 2006, we initiated a 3-year investigation into whether crossing structures provide demographic connectivity for grizzly and black bears in Banff National Park. We collected hair with multiple noninvasive methods to obtain genetic samples from grizzly and black bears around the Bow Valley. Our objectives were to determine the number of male and female grizzly and black bears that use crossing structures; examine spatial and temporal patterns of crossings; and estimate the proportions of grizzly and black bear populations in the Bow Valley that use crossing structures. Fifteen grizzly (7 female, 8 male) and 17 black bears (8 female, 9 male) used wildlife crossing structures. The number of individuals detected at wildlife crossing structures was highly correlated with the number of passages in space and time. Grizzly bears used open crossing structures (e.g., overpasses) more often than constricted crossings (e.g., culverts). Peak use of crossing structures for both bear species occurred in July, when high rates of foraging activity coincide with mating season. We compared the number of bears that used crossings with estimates of population abundance from a related study and determined that substantial percentages of grizzly (15.0% in 2006, 19.8% in 2008) and black bear (17.6% in 2006, 11.0% in 2008) populations used crossing structures. On the basis of our results, we concluded wildlife crossing structures provide demographic connectivity for bear populations in Banff National Park.

Highway verges as habitat providers for small mammals in agrosilvopastoral environments

The Mediterranean Basin has an important conservation value given its high biodiversity and high number of endemic species, which have co-existed with human traditional practices for centuries. However, northern areas as the Iberian Peninsula have experienced intensification in livestock production in recent past, with consequent reduction in habitat quality. In this study we assessed the importance of fenced highway verges as habitat for small mammals in Mediterranean agrosilvopastoral landscapes. More specifically, we compared small mammal abundance between highway verges and the adjacent two main land uses (“montado” and open areas); compared the vegetative structure among these land uses; and addressed how vegetation structure influences species occupancy. Thirty-six sites were sampled in agrosilvopastoral system areas in southern Portugal (sampling effort 8,840 trap-nights). A total of 351 individuals from target species were captured: 157 wood mice (Apodemus sylvaticus), 95 western Mediterranean mice (Mus spretus) and 99 greater white-toothed shrews (Crocidura russula). Capture–mark–recapture analyses were performed to estimate population size. Our data suggests that fenced highway verges promote better vegetative structure conditions which in turn favor a higher animal abundance therein. We suggest the adoption of management practices to increase the height and cover of herbaceous and shrub layers in road verges, together with creating grazing controlled areas in highway vicinity, particularly in “montado” patches, linked by vegetated linear features. This would increase habitat and refuge for a large numbers of species, including small mammals, and thus benefiting the trophic chain and the whole agrosilvopastoral system.

Habitat and corridor function of rights-of-way

This chapter describes the habitat and corridor function of right-of-way habit and includes factors that influence the quality of these functions. Some of the potential problems are also discussed. Species with large home ranges that are not tied to one particular habitat are more likely to use rights-of-way as only part of their home range than species that are sedentary and that have small home ranges than the species that are tied to a specific habitat. Therefore most examples of species that use right-of-way habitat but do not restrict their movements to these relatively narrow strips are birds and larger mammals. While the functions of right-of-way are generally well documented and understood, the corridor function is not. Dispersal, movements over relatively long distances, has rarely been documented. Even though right-of-way habitat and corridors are continuously exposed to disturbance from the roads and traffic, and even though they may be of lesser quality than habitat and corridors away from infrastructure, they can be important to the survival of some species, especially in developed landscapes.

Inter-Individual Variability of Stone Marten Behavioral Responses to a Highway

Efforts to reduce the negative impacts of roads on wildlife may be hindered if individuals within the population vary widely in their responses to roads and mitigation strategies ignore this variability. This knowledge is particularly important for medium-sized carnivores as they are vulnerable to road mortality, while also known to use available road passages (e.g., drainage culverts) for safely crossing highways. Our goal in this study was to assess whether this apparently contradictory pattern of high road-kill numbers associated with a regular use of road passages is attributable to the variation in behavioral responses toward the highway between individuals. We investigated the responses of seven radio-tracked stone martens (Martes foina) to a highway by measuring their utilization distribution, response turning angles and highway crossing patterns. We compared the observed responses to simulated movement parameterized by the observed space use and movement characteristics of each individual, but naïve to the presence of the highway. Our results suggested that martens demonstrate a diversity of responses to the highway, including attraction, indifference, or avoidance. Martens also varied in their highway crossing patterns, with some crossing repeatedly at the same location (often coincident with highway passages). We suspect that the response variability derives from the individuals familiarity of the landscape, including their awareness of highway passage locations. Because of these variable yet potentially attributable responses, we support the use of exclusionary fencing to guide transient (e.g., dispersers) individuals to existing passages to reduce the road-kill risk.