| Summary: | The postfledging period of a passerine bird's life is increasingly recognized as an understudied component of songbird conservation, because the habitat needs of fledglings can differ from nesting adults and survivorship during this period can substantially affect population growth rates. We studied postfledging survival of the Worthington's Marsh Wren (Cistothorus palustris griseus), a state-listed salt marsh songbird subspecies in northeastern Florida, USA, during 2016-2017. Postfledging survival was low during the first 21 d following fledging for the cohort of tracked birds (0.10; 95% confidence interval: 0.01, 0.37). The top a priori model indicated that heavier birds at the time of tagging exhibited greater survival than lighter birds, and birds from larger broods had greater survival than birds from smaller broods. Other covariates not in the top model that also influenced survival included the amount of tall-form smooth cordgrass (Spartina alterniflora) within the natal patch, which positively influenced survival, and the amount of black needlerush (Juncus roemerianus) within the natal patch, which negatively affected survival. The low rates of postfledging survival combined with low rates of nest survival reported elsewhere indicate that Worthington's Marsh Wrens in northeastern Florida require continued protection and warrant further research into management and restoration activities that will improve their habitat.
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