Spatial and temporal factors influencing wildlife use of overpass crossing structures on an Arizona canal

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Kaela M. Hamilton, Applied Biological Sciences, Arizona State University, Mesa, AZ, Thomas Bommarito, U.S. Bureau of Reclamation, Glendale, AZ and Jesse S Lewis, Arizona State University

Background/Question/Methods
Anthropogenic linear corridors (ALCs), including roads, railways, and canals, can reduce landscape connectivity for wildlife on a broad scale. Crossing structures along ALCs have been used to facilitate animal movement across landscapes and maintain connectivity among populations. Spatial factors, including environmental attributes of the surrounding landscape and crossing structure features, as well as temporal factors, such as time of day, can influence whether animals use crossing structures. Compared to roads, little research has evaluated how multiple spatial and temporal scales influence wildlife use of overpass crossing structures on major canals. Our objectives were to evaluate the factors influencing wildlife use of overpass crossing structures on the Central Arizona Project (CAP) canal, and to examine activity patterns of animals using overpasses. We hypothesized that frequency of wildlife use of canal overpasses would vary with overpass dimensions and across environmental gradients. We further hypothesized that activity patterns of wildlife at crossing structures would vary across daily periods. Fifty-two wildlife cameras were deployed along the CAP canal on (a) overpass crossing structures (n=39) and (b) siphons (n=13), which are sections of “natural” landscape where the canal is buried underground. Cameras were deployed in December 2020 and will remain active for one year. Occupancy modeling and activity analysis were used to evaluate wildlife use of overpasses across environmental and structural covariates during the cool-wet season (December – April).
Results/Conclusions
Over a dozen species of small to large-sized mammals were detected at overpasses and siphons on the CAP canal, including coyote (Canis latrans), mule deer (Odocoileus hemionus), bighorn sheep (Ovis canadensis), bobcat (Lynx rufus), and other focal species. The number of species detected varied among crossing structure types (i.e., wildlife bridge, cement overshoot, or siphon) with differing dimensions (i.e., length and width). Consistent with predictions, crossing structure use was influenced by broad and fine-scale environmental features, such as topography, plant productivity, and land cover type. While most animal detections occurred at night, activity patterns for wildlife differed among species and between crossing structure types. Results from this study can be used to inform the long-term management and conservation for wildlife associated with major canals.