Date of Award
Master of Science
Natural Resource Ecology and Management
Stephen J. Dinsmore
Significant landscape alteration has occurred from the westward expansion of European settlement starting in the 18th Century in the form of conversion of large expanses of land to agricultural production. This agricultural expansion was facilitated by the development and installation of artificial subsurface drainage to convert previously saturated and unproductive soil in topographic depressions, also known as prairie potholes, into highly productive tillable areas. Although most are currently drained they still exist in some form and are often observed as sheetwater wetlands in agricultural fields. Sheetwater wetlands have potential value to migratory waterbirds but this value has only been examined in limited spatial and temporal contexts. Many species of shorebirds (order Charadriiformes) undergo bi-annual long distance migrations between temperate and tropical wintering areas to extreme northern latitudes for breeding purposes. During these journeys individuals rely on migratory stopover sites with sufficient resources to refuel energetically and accumulate energy stores in preparation for subsequent migratory bouts. Most previous studies on migratory stopover in shorebirds have been focused on coastal areas or ecosystems; however, many shorebird species migrate through mid-continental areas of North America and rely on network of ephemeral and unpredictable stopover sites in this region. The objective of this study was to document and assess the dynamics and value of agricultural sheetwater wetlands (farmed wetlands) to migratory waterbirds throughout the Prairie Pothole Region in Iowa as well as examine stopover dynamics of Pectoral Sandpipers (Calidris melanotos) at a stopover site in Iowa's Prairie Pothole Region. We hypothesized that these wetlands were common across Iowa's PPR and that they would be largely dependent on local precipitation regimes. Surveys conducted in spring 2011 and spring 2012 resulted in 8415 observations of 519 unique wetlands across ten townships in Iowa's PPR. Wetlands were predominantly observed in a dry or absent state (7399 observations, 87.9%), and when they were observed in a wet state they were predominantly the smaller size classes with the smallest size class of 0-0.1 ha (769 observations) comprising 76.2% of all observations where wetlands contained water and 9.2% of the total (wet and dry) observations. We utilized the multi-state model in program MARK to predict the daily probability of state transition between recorded size classes of wetlands as a response to daily local precipitation. In general precipitation had a strong positive effect on state transitions that characterized wetland size increases and a strong negative effect on state transitions that characterized wetland size decreases. We used spatially replicated road-based surveys to document the presence of water and use by waterbirds (specifically the orders Charadriiformes and Anseriformes) and hypothesized that wetland size and extent would be an important driver of waterbird use in sheetwater wetland habitat. We observed 423 unique wetlands (893 total observations) in 2011 and 96 unique wetlands (123 total observations) in 2012 and frequently documented waterbird use of these wetlands (21.2% of all wetlands). Wetland size was found to have a positive effect on both waterbird species richness and waterbird abundance, and larger wetlands were more likely to be utilized by waterbirds. We did not detect any effect of large tracts of public land within a survey route on either waterbird richness or abundance indicating that waterbirds choose to utilize these wetlands based on their size and availability rather than the local availability of public lands. We also examined stopover dynamics of Pectoral Sandpipers (Calidris melanotos) at a Trumbull Lake in Clay County, Iowa during fall 2012. We radiomarked 52 individuals (19 males and 33 females) and tracked them within this stopover site to determine their departure date. We also modeled daily probability of local survival within the stopover site with the nest survival model on program MARK and utilized daily local survival to estimate minimum stopover durations. We included a body condition index based off of a scaled mass measurement as a covariate in determining daily local survival probabilities. The most competitive model included both a negative linear day-of-season effect and negative effect of body condition index on daily survival rates, with mean minimum stopover duration calculations of 7.4 days (95% confidence interval 4.3 to 13.6 days) across both sexes. The findings from this study provide initial documentation of sheetwater wetlands, their dynamics, waterbird use of this habitat type in Iowa's Prairie Pothole Region, and baseline stopover site use by a common migrant shorebird in the Midwest. These findings will be important for informing future decisions on drainage practices and the impact of these decisions on wildlife, and also indicate the need for further examination of the wildlife value of this habitat type across a larger temporal and spatial scale as well as indicate the benefits of water level management to waterbirds.
Kevin T. Murphy
Murphy, Kevin T., "Waterbird use of dynamic sheetwater wetlands in Iowa's Prairie Pothole Region" (2013). Graduate Theses and Dissertations. 13203.