Sorting out Spatial Distributions and Temporal Population Fluctuations of the Endangered Light-footed Ridgway’s Rail in Southern California Coastal Salt Marshes

Ensuring the long-term availability of adequate coastal salt marsh through management, to support sensitive bird species that rely on these habitats, requires an understanding of the processes that control habitat structure. Southern California coastal salt marshes support a federally endangered marsh obligate bird, the Light-footed Ridgway’s rail. Historical reason for species decline was largely habitat loss from salt marsh conversion to an agricultural and urbanized landscape. Beyond ongoing habitat loss, future concerns are centered around sea level rise and the risk of losing salt marsh habitat due to coastal squeeze. In this research, we investigate habitats associated with rail occurrence, and the driving watershed, marine, and atmospheric forces associated with the size of the annual breeding pair population. We conducted field work at nesting sites, analyzed annual surveys from the past decade, and assessed external forces, like streamflow, to fully describe conditions that support these species. Pairing marsh surface modeling with sediment management techniques (e.g. sediment capture or augmentation) will allow us to model best outcomes for the species. We find that nests are most commonly in cordgrass, as expected, but that bulrush also supports nests. When vegetation other than these two tall grass-like species is predominately used it is a mixture of multiple vegetation species. The most critical variable in predicting rail home range territory was percentage of area that has a marsh elevation between 1.19 and 1.58m (NAVD88). We find that stream flow magnitudes are negatively associated with the annual breeding rail count. A high number of storm events in the past decade is positively associated with breeding pairs, but in the past year there is a negative relationship. These, and other findings, suggest external processes that impact the species in complex ways, for instance the tradeoff between processes that maintain the marsh, like sediment deposition and freshwater influx, but harm the species in the short term by flooding and vegetation scour. This research aims to help salt marsh managers understand the conditions that are associated with rail’s and to delineate management strategies that can be implemented in future years that facilitate marsh accretion in response to rising sea levels.