Graduate Defense: Leticia Camacho

Dissertation Information

Title: Black-tailed Jackrabbit Density in Morley Nelson Birds of Prey National Conservation Area Highlights the Importance of Native
Shrubs

Program: Master of Science in Biology

Advisor: Dr. Jennyffer Cruz, Biological Sciences

Committee Members: Dr. Julie Heath, Biological Sciences and Dr. Jennifer Forbey, Biological Sciences

Abstract

Animals are facing an unprecedented rate of environmental change including extreme rates of habitat loss. Animals may adjust their distribution or behaviors to compensate for changes in food resources and cover associated with habitat loss. We studied how black-tailed jackrabbits (Lepus californicus) in a Western U.S. dryland ecosystem used different vegetation types that provide different levels of food resources and protection. We estimated black-tailed jackrabbit density in 2022 and 2023 within the Morley Nelson Snake River Birds of Prey National Conservation Area (NCA) using repeated spotlight transects and an N-mixture model. Black-tailed jackrabbit abundance increased with increasing shrub cover in 2022 and 2023 and increased also with increasing perennial biomass in 2023. Differences between year effects may have been related to weather conditions. Higher abundances in 2022 (a dry year) compared to 2023 (near-normal, non-drought year with more availability of herbaceous biomass) indicate a potential lag effect in population decline. Although there is some evidence supporting NCA black-tailed jackrabbit population decline compared to the earliest historic raw densities available in the literature (Smith and Nydegger 1985; Knick and Dyer 1997). Our findings suggest prioritizing shrub-dominated habitats with perennial herbaceous vegetation availability to maintain black-tailed jackrabbit abundance hotspots and a unifying spotlight survey methodology for sagebrush ecosystems to fill the 29-year knowledge gap in population density surveys.