Abstract
Secretive marsh birds are difficult to survey for, especially during the non-breeding season when vocalizations are infrequent, complicating population estimation efforts. While some breeding population assessments have been performed, dynamics of marsh bird populations, especially during the non-breeding season along the northern coast of the Gulf of Mexico, remain relatively unknown. To address the void in non-breeding season population information for marsh birds along the coast of Mississippi, we conducted line transect surveys distributed across a spatially-balanced sampling framework of Mississippi tidal marshes December – February, 2018–2020. Using hierarchical distance sampling models for unmarked populations, we estimated species-specific non-breeding population densities and habitat associations of eight marsh bird species across a mosaic of tidal marsh communities, spanning oligohaline to polyhaline emergent and open marsh systems. Marsh Wrens (Cistothorus palustris) were encountered most (n = 1,593) among all surveyed marsh complexes with an estimated coast-wide density of 5.18 ± 1.13 birds/ha. Clapper Rails (Rallus crepitans; n = 606) were also widespread but less dense (0.78 ± 0.33 birds/ha). Seaside Sparrows (Ammospiza maritima; n = 410) on the other hand were more localized within the broader tidal marsh ecosystem with estimated densities ranging from zero when undetected to 3.37 ± 0.78 birds/ha at the Hancock County marsh complex. This study provides the first statewide, non-breeding density estimates for tidal marsh birds along the Mississippi Coast and the first data of these kind for the northern Gulf of Mexico region. These population estimates and density distributions also help increase our understanding of the non-breeding season avian community composition within tidal marshes.
