Disease and the pathogens that cause them are a fundamental driver of population viability in imperiled wildlife species as they can reduce both survival and recruitment

Because species and populations gain listing under the endangered species act (ESA) primarily due to small and diminishing population size, knowledge of their exposure to, or active infections by, population-limiting pathogens and their respective diseases is of critical concern to wildlife managers. The pacific fisher (pekania pennanti PF) is a sensitive forest predator with the southern sierra nevada fisher population segment listed as endangered and throughout northwestern california forests where population status is unknown and of concern. While there are several threats to the pacific fisher, including threats from tree mortality, wildfire, illegal cannabis activity and rodenticides, information about specific diseases affecting this species is limited and continued disease surveillance is needed to better understand population limiting factors. In addition, both the fisher and the northern spotted OWL (strix occidentalis caurina NSO) show evidence that suggests that exposure to rodenticides is an emerging threat to both taxa. For NSO, 70 of NSO livers tested positive for several non-infectious anticoagulant rodenticide agents (ARS), likely linked to pervasive trespass cannabis cultivation. The barred OWL (strix varia BO), a species used as a surrogate for NSO, also indicated high rates of exposure (40 ) in tissues of individuals lethally removed for NSO conservation purposes. The goal of this study is to continue to monitor PF population health by continuing to screen previously collected samples and samples collected during the 2023-2024 season. Here, we propose testing 40 additional blood and fecal sample pairs from these projects for 6 population- limiting pathogens, including short-term and long-term antibody responses, as well as active infections for the most severe of those. Furthermore, we plan to leverage a rare long-term repository of existing pathogen exposure data and untested blood samples to determine prevalence exposure to selected mustelid population limiting pathogens in PF populations throughout california. We also propose to test non-lethal samples (feathers and blood) for pesticide exposures in NSO and BO samples.