Determining the barriers to movement of tule elk at San Luis Reservoir

Cristen Langner, CDFW
Topic Area
Terrestrial Wildlife and Ecosystem Interactions with Transportation

Tule elk (Cervus canadensis nannodes) are native, endemic, need large, contiguous tracts of land to survive, and were almost driven to extinction. Through a captive breeding program, the Department has been able to reintroduce tule elk to native habitat throughout the Central Valley including the area around San Luis Reservoir in Merced County. The San Luis Reservoir herd was started in 1990 with just 26 animals and has grown to approximately 1,000 animals but they are constrained by major highways and canals and are in close proximity to Los Banos, a growing bedroom community for the Bay Area. As the San Luis Reservoir elk population continues to expand, animals will need to be able to disperse to additional habitat. Small populations of elk exist north of Highway 152 and huge tracts of rangeland are available for colonization but due to the size and amount of traffic along the highway, the elk are unable to cross. If elk do attempt to cross, they pose a major human safety concern due to possible vehicle collisions. In addition, High-Speed Rail is slated to pass through Pacheco Pass, which could have major impacts to elk movement in the future. With the human population expected to continue increasing, which increases development and traffic, and the effects of climate change disrupting animals' natural behaviors, habitat connectivity is more important now than ever before. The focus of my study is to document elk movements around San Luis Reservoir to determine critical habitat, movement corridors, and barriers with the ultimate goal of providing the necessary information so an overcrossing can be built. I deployed GPS collars starting in 2015 and continued until February 2018. Each collar was set to collect a GPS location and activity level once every five hours until the last year of deployment when the collection schedule was increased to once every hour to determine more fine scale movements. The collars are set to be deployed for 40 months and then they will drop automatically. Because females and their associates function as a true herd, I deployed one collar in every separate female group that could be located. Bull collars were deployed randomly on spikes up to mature branch bulls to capture the movements different aged males may exhibit. In all, 24 females and 26 males have been collared. Because data collection is still ongoing, formal analysis has not begun. Preliminary review of the spatial data shows approximately half of the animals are interacting with a barrier, including the highways, canals, and a set of electrical transmission lines and four of the collared elk have been killed on Highway 152. Contemporary methods will be used to determine home range sizes, locations, critical habitat, and corridors. Full data analysis is expected to begin in 2020 with results published as appropriate. The data is intended to be used to identify and possibly eliminate barriers to movement, which would increase habitat connectivity and availability for the San Luis Reservoir elk herd.

Abstract Keywords
tule elk