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Variations of Wildlife Safety Crossings and Their Effects for Mule Deer in Northeast Nevada
AuthorSimpson, Nova Oreen
AdvisorStewart, Kelley M.
Natural Resources and Environmental Science
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Organisms move long distances for various reasons including foraging for food, avoidance of predators, increased breeding opportunities, to access seasonal or ephemeral resources, to access seasonal ranges, to expand ranges, or to disperse into new ranges (Bissonette and Adair 2007; Chetkiewicz et al. 2006; Fortin and Agrawal 2005). When barriers are created within a landscape, connectivity among habitat patches is disrupted, and movement between these habitat patches may be limited or eliminated (Bissonette and Adair 2007; Fortin and Agrawal 2005). Barriers to movement may lead to increased mortality, reduced reproduction, smaller populations, and lower population viability because habitat available to each individual declines and gene flow is decreased as populations become increasingly isolated (Bissonette and Adair 2007; Forman et al. 2003). Barriers can also reduce regional population numbers since suitable habitats and resources may become unavailable (Forman et al. 2003). Roads are one anthropogenic factor that can create barriers to movement by species, span over 6.4 million kilometers, and cover over 1 % of the total land cover in the United States (Beckman et al. 2010). Roads also are a leading cause of habitat fragmentation and loss of connectivity among populations in North America and around the world (Beckman et al. 2010). Because of increased habitat fragmentation, corridors have become a fundamental component of management and conservation of wildlife in North America. Traditionally, corridors have been viewed as linear strips of habitat that facilitate the movement of organisms through landscapes, but a form of corridor that has been widely accepted over the last several decades are safe crossing structures designed for wildlife in areas fragmented by roads (also known as safety crossings) (Corlatti et al. 2008; Puth & Wilson 2001; Taylor et al. 1993). The general function of a safety crossing is to provide safe passage for animals to cross either above or below a roadway and remain out of the way of motor vehicles, which can increase safety for both wildlife and motorists (Ford et al. 2008; Kintsch and Cramer 2011). In 2007, Nevada Department of Wildlife and Nevada Department of Transportation started the planning phases to reduce collisions between motor vehicles and migrating mule deer and restore habitat connectivity by placing several crossing structures on U.S. Highway 93 between Wells and Contact, Nevada. Two sites were selected based on known migration routes of mule deer and state reports of deer-vehicle collisions. Construction of the first set of safety crossings, located approximately 16 km north of Wells, was completed in August of 2010. This site is located at 10-Mile Summit and consists of two underpasses, one overpass, and approximately 6.4 km of exclusionary fencing. The second set of safety crossings is located approximately 32 km north of Wells at HD Summit, and was completed in August of 2011. HD Summit consists of one underpass, one overpass, and approximately 4.8 km of exclusionary fencing. The goal of my research was to assess the efficiency of those newly constructed safety crossings and associated exclusionary fencing. Because the crossing structures were built primarily for mule deer, I used mule deer as my focal species. I placed Reconyx HyperFire Professional Cameras with infrared technology at the entrance of each crossing structure to document movement and behaviors of mule deer during migratory periods. I began collecting data during the first migration each site was ready for use without the interruption of construction, and ceased data collection in June of 2012. Since 10-Mile Summit was completed in August of 2010, data was collected during four migrations (autumn 2010, spring 2011, autumn 2011, and spring 2012). Since HD Summit was completed in August of 2011, data was collected during two migrations (autumn 2011 and spring 2012). In chapter 1, my objectives were to document the responses of mule deer to overpasses and underpasses, and to determine which type of structure is most effective for mule deer. I documented behavioral responses of mule deer at the entrance of each crossing structure by observing how mule deer responded to the different structures. I used the number of successful crossings as a measure of the effectiveness of each crossing structure in maintaining landscape connectivity and migration corridors. I used the number of documented traffic-related mortalities as a measure of how effective the safety crossings are in reducing wildlife-vehicle collisions. Mule deer used the crossing structures as soon as they were available. We also observed multiple species using the crossing structures, including one of the first observations of pronghorn (Antilocapra americana) using an overpass. Mule deer responded with more successful crossings and fewer retractions at overpasses compared with underpasses. In addition, mortalities resulting from traffic collisions with mule deer decreased with each subsequent migration. In chapter 2, my objectives were to determine what environmental variables influenced movement and grouping behaviors of mule deer during migratory movements. I used camera data from several wildlife crossing structures to investigate how the season in which movement occurred, time of day, rate of precipitation, percent fullness of the moon, and temperature influenced the total number of crossings and group sizes of mule deer. I hypothesized that migratory movements would decrease with an increase in percent fullness of the moon, ambient temperature, and precipitation, and movements would increase during crepuscular hours. I also hypothesized that group sizes would increase with an increase in the percent fullness of the moon, daylight hours, and rate of precipitation. Lastly, I hypothesized that group sizes would be larger during spring migrations since mule deer are more concentrated on winter ranges and likely synchronize their movements back to summer range with plant phenology. I implemented a model selection procedure to evaluate the importance of those environmental factors, developed a set of a priori models, and allowed my parameters to vary until I retained a set of models that were considered to be the best fit to the data. Movement increased during daylight hours and decreased with an increase in precipitation. Group sizes of mule deer increased with an increase in daylight, intensity of precipitation, and during spring migrations. Contrary to our predictions, we did not document any significant effect of percent fullness of the moon or temperature on movement patterns or group sizes. Highway mitigation projects may be defined as successful when there is a reduction in wildlife-vehicle collision rates and animal movement patterns are restored between habitats fragmented by roadways (Ford et al. 2008; Fortin and Agrawal 2005; Van Wieren and Worm 2001). I demonstrated that the newly constructed safety crossings in Nevada meet those criteria for success. Mule deer used the safety crossings extensively during migratory periods, the number of successful crossings has continued to increase, and the numbers of deer-vehicle collisions have decreased with each subsequent migration. To our knowledge, there are no other studies that have evaluated overpasses and underpasses where both types of structures are within close proximity to each other in the path of ungulates migrating between seasonal ranges. As knowledge increases about the types of structures and features that are successful for wildlife, transportation and wildlife agencies will be able to make more informed decisions on design and implementation of effective safety crossings. Additionally, this research shows changes in group sizes of mule deer with environmental factors including precipitation, seasonality, and time of day, during long-distance migrations, and support other studies that have shown similar changes in environmental factors influence the movements and behaviors of various species (deBruyn & Meeuwig 2001; Harmsen et al. 2011; Kjaer et al. 2008; Penteriana et al. 2011). LITERATURE CITEDBeckmann, J. P., A. P. Clevenger, M. P. Huijser, and J. A. Hilty. 2010. Safe Passages. 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