Spatial and temporal factors influencing wildlife use of overpass crossing structures and landscape siphons along a major canal

Anthropogenic linear infrastructures can reduce landscape connectivity for wildlife, and crossing structures are a mitigation strategy to facilitate animal movement across potential barriers. However, the spatial and temporal factors promoting crossing structure use by the wildlife community across scales are not fully understood, especially for major water canals. We tested multiple hypotheses and predictions to evaluate how wildlife use of crossing structures was influenced by (1) landscape features (i.e., fine landscape-scale vegetation cover and broad landscape-scale plant productivity, topography, and human development), (2) season, and (3) time of day. We used remote cameras to monitor 43 overpasses and 13 siphons (i.e., natural crossing areas where the canal traveled underground) along the Central Arizona Project canal across three seasons (i.e., hot-dry, hot-wet, cool-wet) during one year. We detected 17 small- to large-sized herbivore and carnivore species using overpasses and siphons. When using crossing structures, each wildlife species exhibited unique habitat relationships in relation to vegetation cover, plant productivity, and topography. Several species decreased use of overpasses as the amount of human development increased. Crossing frequency increased in the hot-dry and cool-wet seasons for many species at overpasses (11 species) and siphons (9 species). Daily activity patterns of individual species were similar across seasons, and between overpasses and siphons. Ultimately, this study suggests that to promote movement across canals for the wildlife community, it is important to provide a variety of crossing types that occur away from human development and across a range of vegetation and topographic characteristics.