Marsh birds as ecological performance indicators for Lake Ontario outflow regulation

Water-level regulation can have significant impacts on coastal wetland ecosystems. In this study we sought to update marsh-bird-based ecological performance indicators (PIs) that support adaptive management of long-term outflow regulation for Lake Ontario. Previous PIs established in the mid-2000 s were based on single species and monitoring them required data not currently being collected at broad scales. We therefore focused on developing and validating community-level PIs using data from an ongoing, long-term, basin-wide monitoring program, the Coastal Wetland Monitoring Program (CWMP). After identifying species with documented responses to variation in water levels in the literature, we considered a suite of potential PIs by first examining correlations with both annual mean water levels and measures of interannual water-level fluctuations. We then used a mixed-modelling framework to determine which highly correlated PIs exhibited statistically significant relationships with water-level variables. Having established significant effects of water levels on the candidate PIs, we performed a power-sensitivity analysis to determine the degree of change in each PI that can be detected based on current CWMP sampling. From these analyses, we propose six potential marsh-bird based PIs: sum total abundance of sensitive marsh-obligate species, richness of sensitive marsh-obligate species, and abundance of each of red-winged blackbird (Agelaius phoeniceus), marsh wren (Cistothorus palustris), common gallinule (Gallinula galeata), and least bittern (Ixobrychus exilis). Of these, the community-based PIs of sum total abundance and richness of sensitive species appear most suitable for assessing the marsh-bird community response to outflow regulation on Lake Ontario.