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Habitat Quality, Climate, and Waterbird Fitness in Montane Wetlands

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Red Rock Lakes National Wildlife refuge is located in the Centennial Valley of southwest Montana. The Refuge encompasses approximately 10,000 ha of natural and created montane wetlands at an elevation of 1,676 m, providing reproductive and migratory habitat for a diverse waterbird community. Approximately 2,300 ha of the wetland complex (i.e. Lower Red Rock Lake) are affected by a water control structure, permitting water level manipulation of a large portion of wetland habitat on the Refuge. Current refuge objectives for wetland habitat management are to mimic disturbance processes believed necessary for maintaining ecological function of montane wetlands. The primary process of management interest is the dynamic wet/dry hydrological cycle, a key driver of wetland productivity and vegetation community structure. The ability to manipulate water levels on Lower Red Rock Lake allows the Refuge to control, to some degree, the primary disturbance regime for that ecosystem. However, the Refuge has little ability to predict the outcome of such manipulations. Therefore, the Refuge has initiated an adaptive resource management plan that provides a framework within which objective decisions can be made and the uncertainty surrounding those decisions reduced. In this way, management can evolve as more information about the system is gained and uncertainty is reduced.

The primary objective of the Lower Lake plan is to return the submerged aquatic vegetation community to an historical composition observed prior to impounding. Specifically, the objective is to “increase the percent coverage of Potamogeton spp. and Elodea spp., collectively, to > 40% in Lower Red Rock Lake within 10 years”. Reduced Lower Lake water levels (drawdowns) during key times are being implemented in an effort to bring about the desired change in submergent composition. Occurring concurrently with water-level manipulations, monitoring of submergent community composition is providing a means of quantifying the relative success of manipulations. The Lower Lake plan has being undertaken based upon the assumption that the target submergent community provides higher quality habitat than the current condition, and therefore should result in increased fitness of breeding waterbirds utilizing Lower Lake habitats.

We are conducting a mark-recapture study, concurrent with the implementation of the Lower Lake plan, to quantify survival and recruitment for several species of waterbirds that utilize Lower Lake habitats for reproduction. Monitoring waterbird survival and recruitment will provide a unique opportunity for the Refuge to advance understanding of montane wetlands and the migratory birds dependent upon them, while testing key assumptions of Refuge wetland management. We are quantifying key habitat components (e.g., water level, area of flooded emergent vegetation, and submergent composition), climate parameters (e.g., precipitation events and daily/weekly temperature), and seasonal survival and annual recruitment of several waterbird species.

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