Drivers of productivity in a tidal marsh specialist bird species ( Rallus crepitans )

Abstract

Effective conservation efforts are contingent on understanding the underlying demographic processes that regulate wildlife populations. Productivity is a key driver of population growth, and in avian taxa, nest survival and clutch size dictate the number of chicks successfully hatched. Patterns in productivity can vary spatially and temporally, shaping populations and their evolutionary trajectories. We evaluated potential drivers of nest survival and clutch size in a declining, salt marsh specialist bird species, Rallus crepitans (Clapper Rail) using data from 2019 to 2021 modeled with a Bayesian logistic exposure model. Nest survival probabilities varied across sites and incubation stage, but vegetation thickness (visual obscurity) and the timing of nesting affected nest survival the most. Nest survival peaked in the middle of the breeding season, coinciding with an increase in clutch size and an apparent larger number of concurrent active nests. Despite tidal flooding, nest failures largely occurred due to predation, suggesting that the dilution effect in the mid-season coupled with thicker vegetation around the nest lead to the highest probability of nest success. Increases in clutch size during the periods of highest survival suggest adaptive timing in reproductive investment. Our findings highlight the importance of appropriately timing restoration and other vegetation management efforts in marshes to minimize impacts during the breeding season and provide a contemporary estimate of nest survival in this declining population.