Modeling wetland use by spring-migrating lesser scaup (Aythya affinis) in eastern South Dakota

The continental population of lesser scaup (Aythya affinis [Eyton]; hereafter scaup) has been in decline since the 1980s, leading researchers to speculate that poor habitat and reduced feeding efficiency during spring migration have resulted in lower body condition thereby impacting reproductive success. In this study, I assessed scaup-habitat relationships to determine the variables that best described scaup use of wetlands in South Dakota's Prairie Pothole Region (PPR), an important part of their migration route. Empirical data were used to develop a temporally dynamic spatial model to describe historic habitat suitability in the PPR between the years 1950 to 2000. Empirical data showed that amphipod abundance, wetland size and wetland habitat at the landscape scale played important roles in habitat selection. I then developed a spatial habitat suitability index model comprised of three sub-models: (1) a population and rule-based sub-model describing potential amphipod production (AMPROD) in response to seasonal climate, (2) a landscape sub-model describing changes in total wetland area at broad scales and (3) a sub-model accounting for changes in open water area. Indices for each of the three sub-models were derived using WETSIM (Version 3.1), a process oriented wetland model that simulates the hydrodynamic and vegetation changes of a semipermanent PPR wetland from climate data. The model predicted high spatial and temporal variation between stations in response to local climate, however, stations that were closer together tended to be more similar. Average long-term habitat suitability was predicted to be highest in the eastern portions of the PPR, where climate conditions produce more favorable habitat than the west and north. The model does not fully support the spring condition hypothesis (SCH), which postulates that migration habitat suitability in the upper-Midwest has declined since the 1980s. However, it predicts that migration habitat suitability is cyclic. This raises serious concerns for migration habitat losses currently occurring in the eastern PPR, and interestingly indicates habitat declines in areas where the SCH was formulated. The model also raises questions relating to the metapopulation dynamics of amphipode in the western PPR, which are presumed to experience higher local extinction rates due to higher drought frequency.