Pennyroyal Plain Parulids: Characterizing Louisiana Waterthrush occupied stream reaches in an agriculturally-dominated landscape using a standardized bioassessment
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The Western Pennyroyal Karst Plain (U.S. Environmental Protection Agency Ecoregion 71e, often shortened to “Pennyroyal Plain”) historically was composed of open oak savanna and tallgrass prairie, but its relatively flat topography and abundance of treeless terrain lent to its conversion to predominantly agricultural land. This change in the landscape is to the detriment of instream and riparian community composition, as agriculture results in increases in sedimentation, nutrient input, alterations in stream flowpaths, and riparian zone deforestation. A riparian-obligate songbird, the Louisiana Waterthrush (Parkesia motacilla, family Parulidae) has been proposed as a bioindicator due to its reliance on relatively high-quality stream and riparian habitat to feed itself and its nestlings. On the Pennyroyal Plain, the waterthrush is met by seemingly unfavorable conditions of narrow riparian forest buffers and few aboveground streams, many of which are impacted by intensive row crop agriculture. In order to characterize the conditions in which waterthrush may be found in this ecoregion, I surveyed for waterthrush, sampled instream macroinvertebrates in accordance to Tennessee Department of the Environment and Conservation bioassessment protocols, and performed analyses of forested buffer width, land cover, and minor tributary confluences using GIS. Waterthrush were found at all sites during either surveys or during macroinvertebrate sampling. Bioassessment results classified sites as having impacts including bank sloughing, reduction of riparian vegetation, and reduced forested buffer width. Biotic index scores exceeded target scores for four out of seven sites, though even at those sites, some taxa and functional groups were not well represented. Forested buffer widths regularly reached 60-100m, but were not consistently as wide as 200m. Land cover in the surveyed watersheds revealed predominantly agricultural land use, and low percentages of residential and commercial development. The conditions in which these waterthrush have been found suggest some ability for adults to tolerate agriculturally impacted streams, though their presence does not necessarily indicate nesting success. Further work is needed to ascertain what habitat details are most important to waterthrush – whether singly, as pairs, or to support nestlings.