The endangered salt marsh harvest mouse (Reithrodontomys raviventris; SMHM) is endemic to the marshes of the San Francisco Estuary. This species is actively managed as a habitat specialist dependent on tidal marshes dominated by pickleweed (Salicornia pacifica). In reality, their realized niche is much broader, and recent research has continued to reveal flexibility in their habitat requirements. However, an abundance of research failed to accurately identify the primary constituent elements that determine occupancy and abundance throughout the species range. This lack of a more nuanced understanding of habitat requirements causes challenges for biologists attempting to evaluate the potential for SMHM occupancy at many sites, and presence is often assumed if any pickleweed marsh occurs. Based on recent demographic, diet, and habitat use data we propose that SMHM persistence is dependent upon four primary constituent elements-foraging habitat, refuge habitat, nesting habitat, and dispersal habitat – and describe here the essential characteristics of each of these elements. It is our hope that a standardized framework for evaluating these essential characteristics will provide biologists the tools they need to assess areas of potential SMHM occupancy in a more efficient, effective, and consistent manner, which can streamline permitting decisions and recovery plans.

My name is Carla Angulo and I am a graduate student on the MS Environmental Management program at the University of San Francisco and currently a Biologist for WRA, Inc. I have worked and collaborated in research on the salt marsh harvest mouse since 2013. I assisted in trapping and radio tracking during the most comprehensive research effort in the San Francisco Estuary, which has allowed me to become an expert in salt marsh harvest mouse habitat.