Importance of visibility when evaluating animal response to roads

Abstract

Roads increase risk to animals via direct and indirect mechanisms yet, both positive and negative effects of animal space use in relation to roads have been reported. These contrasting reports may not actually represent animal ecology, but could be a product of the primary variable used to test the relationship between animals and roads. Animal‐road associations are often evaluated using Euclidean distance. Euclidean, or straight‐line, distance fails to account for the screening effects of vegetation and topography and may document spurious relationships. We evaluated the influence of Euclidean distance, visibility from road and forage quality on summer space use for male elk Cervus elaphus and female elk subherds in Custer State Park, South Dakota, USA. Models that included interactions with visibility from road metrics outperformed models that included only Euclidean distance to road as main effects. Elk response to roads varied by sex and road type, which functioned as an index for vehicle use. Male elk selected habitat away from roads with the greatest vehicle use, an effect that was greater if habitat was visible from those roads. Female elk tended to select habitat with high forage quality in areas visible from roads closed to vehicle use. Interestingly, both male and female elk selected habitat away from roads with secondary vehicle use and near to roads devoid of traffic, regardless of visibility. Our analysis highlights the importance of including both Euclidean distance and visibility from road metrics. Road effects research may be incomplete without consideration of visibility from roads, particularly for large mammals in landscapes with intense road use.

Elk resource selection at parturition sites, Black Hills, South Dakota

“…We primarily developed models to evaluate whether forage or hiding cover components were being selected across spatial scales (Thomas et al , Barbknecht et al , Rearden et al ). We considered additional models where we evaluated terrain characteristics related to predation and road avoidance, and road density associated with human disturbance across spatial scales (Edge and Marcum , Koehler and Hornocker , Millspaugh et al , Laundré and Hernández , Montgomery et al ).…”

The effects of power lines on ungulates and implications for power line routing and rights-of-way management

“…The scale considered may invert the conclusions . The ability to see or hear power lines may be an important factor to be considered, as for roads (Montgomery et al, 2012).…”

Spatial variation in the density and vulnerability of preferred prey in the landscape shape patterns of Amur tiger habitat use

“…The results of this procedure were evaluation grids, at a 50 m resolution, where the height of the UD refers to the likelihood of tiger habitat use within the home range. We next converted UD height to percentiles where the highest‐use area of the home range corresponds to the 1st UD percentile and the lowest probability of habitat use corresponds to the 95th UD percentile (Montgomery et al , ). This approach differs from the traditional resource utilization function (Marzluff et al ) in that the conversion of the UD height to percentiles standardizes the response variable across individuals.…”

“…Determining the factors that affect patterns of animal habitat use within the home range provides insight into species ecology, population demography, and resource selection while informing management and conservation initiatives (Woodroffe and Ginsberg , Rhodes et al , Loveridge et al , Montgomery et al ). Ecological theory and empirical research suggest that carnivore habitat use is affected by the dispersion and characteristics of resource patches (Macdonald , Carr and Macdonald , Valeix et al ), and more specifically prey availability and accessibility (Macdonald , Stephens and Krebs ).…”