ABSTRACT
Johnson, E.I.; Percy, K.L.; Fox, D.M., and Stouffer, P.C, 0000. Declines of migratory songbirds in a deteriorating swamp forest: A link to baldcypress leafroller outbreaks.
Forested wetlands exist in a balance of hydrologic conditions that facilitate flooding and periodic drying, making their long-term sustainability vulnerable to hydrologic disruptions. Coastal Louisiana baldcypress-tupelo swamp forests have experienced multiple threats over the last 150 years, first by nearly complete clear-cutting, and then through damming and leveeing of rivers and deltaic distributaries. Maurepas Swamp is the second largest swamp forest in the United States, but historical hydrologic disruptions combined with subsidence have left it persistently flooded, thereby preventing tree regeneration. This study examined changes in bird and caterpillar populations between 2003–05 and 2019–20, predicting that swamp specialist birds and caterpillars would be disproportionately affected by deteriorating conditions compared to forest generalists. Standardized point counts were conducted to estimate bird density between closed-canopy relict and open-canopy degraded swamp forest sections and time periods, and a distance-based hierarchical modeling approach was used to adjust for imperfect detection. The U.S. Forest Service National Insect Disease Survey database was examined to assess lepidopteran outbreak frequency and extent, and a longitudinal mixed effects logistic regression model was used to measure temporal changes. As predicted, three swamp specialist bird species (Prothonotary Warbler [Protonotaria citrea], Northern Parula [Setophaga americana], and Yellow-throated Warbler [Setophaga dominica]) decreased in density by >50% over the study period, concordant with a reduction of baldcypress leafroller caterpillar (Archips goyerana) outbreaks after 2006. Generalist Red-bellied Woodpeckers (Melanerpes carolinus) decreased less dramatically through time, perhaps explained by regional rather than localized mechanisms. In contrast, 12 of 16 generalist bird species densities remained stable or increased over time, as did forest tent caterpillar (Malacosoma disstria) outbreaks. Decreases in baldcypress leafroller outbreak extent and frequency may be driven by decreased nutrient availability corresponding to hydrologic impoundment, suggesting that restoration of hydrologic connectivity to freshwater inputs may be critical for restoring swamp wildlife food webs.
