The objective of this project is to develop effective, cost-efficient, and long-term management strategies for the Least Bell’s Vireo (Vireo bellii pusillus) by analyzing how multiple, interacting stressors affect its populations in Southern California. To achieve this, the team will create a spatially explicit agent based model called Recovering Endangered Species with Emerging Threats (RESET) to assess these stressors and test management approaches. While tailored to the Least Bell’s Vireo, RESET will be designed as a flexible tool adaptable to other listed species in arid and semiarid stream systems of the western United States.

The Least Bell’s Vireo nests in narrow riparian corridors surrounded by dense urban development. Some of the largest remaining nesting areas are found on U.S. Department of Defense (DoD) military training lands and in U.S. Army Corps of Engineers (USACE) flood control basins. Managing this species is both operationally complex and financially burdensome, with costs among the highest for any listed bird species.

RESET will be developed to address the specific case of LBVI; however, it will also be designed as a flexible framework to address problems with other listed species along arid and semiarid streams in the western United States. The model will include inputs and submodels for stressors related to groundwater extraction, loss of streamflow inputs due to water recycling programs, changing flood and fire regimes, nest parasitism by Molotrhus ater, and negative impacts to riparian vegetation from invasive non-native plants and insects. The project team will take a strong inference approach to the design of simulation experiments to isolate the effects of individual stressors and to understand how multiple, interacting stressors may affect the distribution and quality of LBVI nesting habitat, reproductive performance, and metapopulation dynamics. Based on this information, the project team will use simulation experiments to compare a suite of alternative management strategies to understand how specific management actions directed at one or more of these stressors may improve LBVI nesting habitat conditions, alleviate key threats, and provide the least cost path to recovery.

RESET will provide DoD, USACE, and other action agencies with a novel tool for predicting the effects of specific stressors and associated management strategies on Least Bell’s Vireo (LBVI) populations at local, regional, and range-wide scales. Model analyses will directly inform future management decisions and resource allocation on military installations and civil works projects, where regulatory compliance often incurs significant costs. Specifically, the model will support development of a conservation plan for USACE that enhances operational flexibility while improving outcomes for LBVI. It may also be used to inform other priorities outlined in recent U.S. Fish and Wildlife Service (USFWS) guidance for LBVI recovery (USFWS 2020a), such as designing cost-effective cowbird control or regional strategies for managing invasive plants. Importantly, outcomes from simulation experiments will be expressed as distributions of possible results, reflecting the natural variability of riparian systems and uncertainties related to interacting stressors and emerging threats (Anticipated Project Completion - 2026)