Recipient of the 1999 Outstanding Master's Thesis Award - First Place.
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Open Access Thesis
Birds--Breeding; Birds--Habitat; Grassland animals--Behavior;
Intensively managed rotational grazing is a grazing method in which livestock are moved through a series of paddocks over a three to six week rotation. Vegetation in resting paddocks is allowed to regrow, renew energy reserves, and rebuild plant vigor to provide nutritious forage for livestock. Consequently, vegetation in the paddocks is in different stages of growth which creates a mosaic of vegetation heights across the pasture landscape. I hypothesized that the mosaic of vegetation heights resembles the native tallgrass prairie grazed by bison prior to European settlement. The mosaic may be attractive and beneficial to breeding grassland birds. Several species of Neotropical migrant grassland birds have experienced severe declines in the past 30-40 years due to loss of habitat and intensified agricultural practices. Intensive rotational grazing as a sustainable alternative to conventional row crop agriculture and continuous grazing systems may provide better breeding habitat for grassland birds.
To test my hypothesis, I assessed and compared bird use in six rotational grazing pastures, two native prairies, and one native savanna in Northeast Iowa. I conducted early morning bird counts using a fixed width transect method. Each site was censused six times between May and August 1996. Bird abundance and species richness were compared between pastures and native grasslands. I also assessed vegetation structure and landscape level features at each site to determine what features might attract grassland birds.
Each study site is unique in its management, vegetation, adjacent habitat, and landscape scale feature. Thus, each site was considered and analyzed individually. I also tested for differences between native and grazed sites. T-tests showed no significant difference between grazed pastures and native sites for total species richness, grassland species richness, woodland species richness, Neotropical migrant grassland species richness, Shannon-Weaver index of diversity, total grassland species abundance, bobolink abundance, dickcissel abundance, meadowlark abundance, and grasshopper sparrow abundance. The comparisons allow me to conclude that rotationally grazed pastures are acting as native grassland analogs and are a good alternative to conventional farming in human dominated landscapes.
Year of Submission
Year of Award
Master of Science
Department of Biology
Tallgrass Prairie Center
Laura Jackson, Chair, Thesis Committee
1 PDF file (vii, 66 pages)
©1998 Jennifer Marie Hurley O'Hara
O'Hara, Jennifer Marie Hurley, "Breeding bird use of intensively managed rotational grazing pastures, native prairies and savannas: A comparison" (1998). Dissertations and Theses @ UNI. 654.