Landscape Predictors of Mule Deer Road Crossing Behavior in the American Southwest

Abstract

Road networks pose many well-documented threats to wildlife, from fragmenting habitats and restricting movement to causing mortality through vehicle collisions. For large, wideranging mammals like mule deer (Odocoileus hemionus), home range requirements and seasonal migrations often necessitate road crossings, posing threats to human safety, property, and deer survival. Research has shown wildlife road crossings and wildlife-vehicle collisions cluster in response to environmental factors. Although general relationships between crossings, collisions, and landscape features have been described, there is variation across locations and species in predictors of crossing frequency and collision risk. We aim to evaluate the extent to which various landscape, environmental, and human factors influence the location and timing of mule deer road crossings near Salt Lake City, UT. Specifically, we are interested in understanding how elevated artificial nightlight may influence deer road crossing locations. By integrating the latest NASA nightlight products with GPS collar data collected from 67 mule deer over a 7-year period (2012 to 2018), we used a resourceselection framework to assess factors influencing seasonal crossing behavior and intensities within individual seasonal home ranges at a variety of spatial scales (fine: 20m, median hourly movement: 55.33m, and median daily movement: 573.33m). Findings indicate both anthropogenic and environmental factors influence mule deer road crossings. Areas with more shrub cover and vegetative greenness (NDVI) increased the likelihood of crossing, whereas sections of road with faster speed limits reduced crossings. Artificial nightlight also had a significant influence on whether road segments were crossed. Deer avoided crossing available roads in their home ranges with elevated nightlight in both summer and winter, especially during crepuscular and nighttime periods. However, lower nightlight levels were also associated with increased risk of road mortality, as were higher speed limits and less surrounding shrub cover. Increased knowledge about factors influencing road crossing behavior, especially factors that may attract or repel human-tolerant wildlife species from roadways, presents an opportunity to mitigate collision risk while improving population management strategies for an economically and ecologically important species in an expanding metropolitan area.