Breeding ecology of the Seaside Sparrow (Ammodramus maritimus) in northern Gulf of Mexico tidal salt marshes

Abstract

Tidal salt marshes are critically important habitats that have experienced serious declines in the United States and still face current and future threats. Marsh birds have been proposed as potential indicators of tidal marsh integrity, yet the basic biology of many species remains poorly studied along the coast of the Gulf of Mexico. I examined factors affecting nest-site selection, nest success, density, and extra-pair paternity of a tidal marsh obligate passerine, the Seaside Sparrow (Ammodramus maritimus), in two marsh complexes on the Mississippi coast. Nest placement and survival both appear to be strongly influenced by predation. Nests were built in areas with more ground cover than random points and better-concealed nests were more likely to fledge young. These results contrast with those from Atlantic coast tidal marshes, where nest placement and nest survival are both driven by tidal flooding. Survival was higher for nests that had closer active neighbors and successful nests were spatially clustered, while unsuccessful nests were not. More research is needed to determine if Seaside Sparrows are clustering in areas of low predator potential or if higher densities of birds can more effectively drive off or warn one another or predators. Elevation and Seaside Sparrow density were positively related in our study marsh, a result that contrasts with patterns of occupancy at a broader scale. I suggest that because broad- and fine-scale habitat relationships do not always agree, both must be considered when predicting species-level responses to potential future habitat alterations. I found that extra-pair paternity in my study populations did not seem to have any adaptive benefit for females and they may be unwilling extra-pair partners. Further research is needed to confirm and clarify these results, but it is possible that extra-pair paternity represents a case of sexual conflict in our populations. While research across a broader area of the northern Gulf of Mexico is still needed, the results of this study will contribute to a better understanding of the demography and habitat relationships of the Seaside Sparrow and will increase its usefulness as an indicator for tidal marsh integrity.