Tidal marsh ecosystems are expected to change significantly over the next century in the northern Gulf of Mexico. Potential threats include climate-related stressors: sea level rise will inundate current habitat, changes in precipitation patterns will significantly change salinity of marshes, and hurricanes can drastically alter the tidal marsh landscape. For tidal marsh endemics like Clapper Rails (Rallus crepitans) environmental changes create uncertainty around their future population status and distribution. We initiated standardized call-broad-cast marsh bird point counts during the spring/summer of 2005 in two tidal marsh systems in coastal Mississippi, continued through 2008. The two sites, the Grand Bay and Pascagoula River marshes, capture the two broad marsh types of the northern Gulf of Mexico; Grand Bay marshes are typically marine-dominated marshes whereas the Pascagoula Marshes are usually oligohaline, characterized by higher floristic diversity. We took advantage of marsh bird abundance data collected pre- and post-hurricane Katrina to investigate the impacts of this hurricane on marsh bird populations. Specifically, we asked if marsh bird abundances change correlate with hurricane Katrina and if so, how these changes differed between our two focal marsh complexes, and post event.
Based on our initial analysis, Clapper Rail populations differed significantly between the two marsh complexes. Pre-hurricane rails densities at Grand Bay were 2.9 + 0.5 birds/ha and only 0.5 + 0.25 birds/ha in the Pascagoula marshes. Post-hurricane Katrina densities declined significantly to 0.45 + 0.2 in the Grand Bay Estuary with only a slight decline in the Pascagoula marshes (0.35 + 0.1). In the second year following hurricane Katrina, Grand Bay Clapper Rail populations rebounded to pre-hurricane levels (2.8 + 0.35) yet densities continued to decline on the Pascagoula (0.25 + 0.05). Beginning in 2008, rail densities began to rebound in the Pascagoula River marshes although we did not conduct marsh bird surveys at this marsh complex in 2009. Field observations suggest elevated salinities associated with hurricane Katrina storm surge caused a significant decrease in vegetation cover in the more freshwater marshes of the Pascagoula compared to the more salinity tolerant vegetation cover at Grand Bay. Assessment of the sensitivity of Clapper Rail populations to disturbance reveal populations respond to proximal conditions, quickly rebounding in number after major disturbance, although their rate of response is clearly linked to differing ecological conditions.