Date of Award
Master of Science
Natural Resource Ecology and Management
Stephen J. Dinsmore
Population monitoring is crucial to the effective conservation and management of a species because it identifies declining population trends before the species is at risk of extinction. The overall goal of our project was to understand distribution, abundance, and habitat associations of secretive marsh-birds, as well as refine national protocols for future monitoring in Iowa. To assess distribution and abundance, we modeled detection probability and obtained density estimates of four species of marsh-birds (pied-billed grebe, least bittern, Virginia rail, and sora) in three different regions of Iowa. We evaluated wetland occupancy of the same four species of marsh-birds relative to wetland characteristics to investigate habitat associations. Lastly, to refine survey protocols, we compared response rates to call-broadcasts of secretive marsh-birds between morning and evening survey periods and between early and late in the survey season. I estimated population density ranged from 0.019 birds/ha for least bitterns to 0.12 birds/ha for pied-billed grebes. I concluded that density of each species was different in different areas of the state due to contrasting microhabitat characteristics. I found that wetland size was the single habitat characteristic that positively affected probability of occupancy of all species. I also concluded that water depth and percent coverage and height of emergent vegetation (specifically cattail) were important characteristics affecting wetland occupancy by marsh-birds. Lastly, I determined that response rates of secretive marsh-birds vary between early and late in the survey season. Response rates varied by time of day for pied-billed grebes only, although this variation was only evident late in the survey season. Overall, this study increased our general knowledge about population status and habitat associations of secretive marsh-birds in Iowa. I hope that information from this study will guide future marsh-bird research and monitoring, as well as wetland restoration and management decisions.
Harms, Tyler, "Population ecology and monitoring of secretive marsh-birds in Iowa" (2011). Graduate Theses and Dissertations. 12218.