Development of avian metrics to monitor salt marsh integrity
Date
2010
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Publisher
University of Delaware
Abstract
Salt marshes are dynamic, highly productive ecosystems that have historically experienced a variety of anthropogenic alterations. Such changes have caused a number of endemic species to become high conservation priorities in the United States. Salt marsh condition must be monitored to develop successful management strategies for wildlife conservation. Avian community structure was evaluated and used to create a Marsh Bird Community Integrity Index (BCI) to assess marsh condition at 184 points across nine Northeast national wildlife refuges (NWR) and refuge complexes. Mean refuge BCI was greatest at E.B. Forsythe NWR and mean survey point BCI was significantly different between marshes of different marsh management types (e.g. ditched, tidal restricted, reference) at four refuges. At the local scale, BCI was positively influenced by percent cover of high marsh and negatively influenced by percent cover of open water. At the landscape scale, BCI was negatively influenced by percent cover of forest, development, and palustrine wetland. A BCI scale can be used to monitor temporal and spatial variations in BCI and to attribute condition labels, “Good”, “Caution”, and “Concern”, to refuge marshes. Monitoring plays an integral role in wildlife conservation efforts; however most monitoring programs are fiscally constrained and must determine how to acquire needed information with minimal resources. Monitoring objectives may be achieved by supplementing costlier intensive assessment metrics with appropriate cost-efficient rapid metrics, and by monitoring specific taxa as indicators of ecosystem health. A subset of the 184 points, located at the Coastal Delaware NWR Complex, was used to evaluate differences in rapid versus intensive avian assessment metrics. Overall, occupancy and relative abundance estimations for four tidal marsh obligate species increased as number of visits increased, however there was a greater positive effect of number of visits on differences between relative abundance estimates than occupancy estimates. Comparisons between metrics of a potential indicator species, Seaside Sparrow, resulted in significant positive relationships between the rapid metric relative abundance and intensive avian metrics, nest density, fledgling density, and territory density. This research supports using birds to monitor the ecological condition of the surrounding salt marsh to improve management decisions and maximize conservation gains.