Date of Award

Winter 1-12-2026

Document Type

Thesis: Open Access

Degree Name

MS Marine Science

Department

Environmental and Ocean Sciences

Committee Chair

Drew Talley

Committee Co-Chair

Jeff Crooks

Committee Member

Hiram Moreno

Committee Member

Justyn Stahl

Committee Member

Richard Zembal

Abstract

The state and federally endangered light-footed Ridgway’s rail (LFRR; Rallus obsoletus levipes) is central to regional conservation, yet the drivers of its population fluctuations remain poorly understood. The fragmented nature of coastal wetlands in Southern California is threatening the existence of endemic species like the LFRR. Tidal inundation, severe storms, and overpredation threaten the survival of LFRR. This study addresses population fluctuations by analyzing the spatial and temporal drivers of LFRR populations to inform effective, site-specific management.

To do this, a 45-year (1980–2024) LFRR census data set across 16 wetlands throughout its range in California was synthesized. A multi-faceted approach was utilized, including: (1) a spatial analysis using linear regression to correlate population size with habitat characteristics (size, richness, and type); (2) a temporal analysis using pairwise Pearson correlations and non-metric multidimensional scaling (nMDS) to assess population synchrony and its relationship to climatic variables (e.g., the El Niño Southern Oscillation [ENSO]); and (3) a discussion of management actions, including a captive breeding and release program.

In California in 2024, 57% of the total LFRR population resided in just three marshes, highlighting the species' vulnerability to localized threats. Analyses revealed low-to-moderate overall population synchrony (mean Pearson correlation = 0.37), indicating that local, site-specific factors may be the predominant drivers of year-to-year LFRR population dynamics. While habitat size and richness are significant predictors of LFRR annual population size and climatic events (e.g., ENSO) can trigger regional population declines, the effectiveness of conservation actions (e.g., population supplementation) is dependent on local conditions consistent with other low-synchrony systems.

The recovery of the light-footed Ridgway’s rail requires management actions, from habitat restoration to population supplementation, which are tailored to the unique ecology of each individual wetland.

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