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The Role of Small Mitigation Wetlands in Supporting Fall Migrating Waterfowl
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Alldred, Mary, Mihuc, Tim, Garneau, Danielle
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Spring 2025
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While wetland mitigation aims to offset disturbances to wetland habitats, it often falls short in matching the ecological function, size, and quality of the originally disturbed area. Further, the criteria for defining wetland mitigation success are a matter of debate, and current practices often fail to evaluate success based on management goals. When evaluating mitigation success, it can be useful to establish criteria based on specific wetland functions, like habitat that supports wildlife. We used a stratified sampling design to estimate forage availability and energetic carrying capacity (ECC) for waterfowl in mitigation wetlands along a quality gradient in the Lake Champlain Valley of New York state. Vegetation and invertebrate food sources were sampled to estimate forage biomass (kg/ha) and ECC in terms of duck-energy days (DED/ha). Our results revealed significant variation in forage availability and DEDs across the quality gradient, with a more than 20-fold increase in DEDs from the lowest to highest quality sites. Submergent marsh vegetation provided the highest unweighted mean DEDs in most study areas. While invertebrate food sources were relatively insignificant overall, they played a more substantial role in poor-quality wetlands. The study highlights the importance of conserving wetland quality, not just acreage, in mitigation efforts and demonstrates that small mitigation wetlands can contribute significantly to waterfowl habitat if properly managed. These findings emphasize the need for more rigorous standards in wetland mitigation projects and suggest using alternative means, like ECC for waterfowl, for defining mitigation success based on management goals. Further, we investigated the relationship between ECC for waterfowl and waterfowl use of small mitigation wetlands. To do this, we conducted game camera surveys at three of the five study areas—one low quality, one medium quality, and one high quality—based on a rapid qualitative assessment and our ECC results. Two daily surveys were conducted using the game cameras from September 1st – December 17th, 2023. We found no relationship between site quality and number of waterfowl observed, suggesting other drivers of waterfowl habitat selection like abundance of emergent vegetation, proximity to open water, and disturbance regime. This study demonstrates the need for managing mitigation wetlands wholistically for a variety of species, both flora and fauna, with a focus on habitat heterogeneity and connectivity. Additionally, this study highlights the advantages and disadvantages of low-cost ecological sampling methods like game cameras and autonomous recording units. Further research is required to better understand waterfowl habitat selection drivers and the significance of small mitigation wetlands across the landscape for more than just waterfowl.