Nest Survival of Grassland Breeding Birds in a Southern Mixed-Grass Prairie Wetland

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Helms, Clinton
nest; survival; sparrow; meadowlark; grassland; Biology; Life Sciences
thesis / dissertation description
As a group, grassland birds have been declining significantly since European settlement of the prairie. The subsequent plowing of the prairie by settlers was compounded by fire suppression, resulting in a patchwork of cultivated fields with intermittent tracts of overgrown grassland. Over an interval of ~200 years, these practices lead to an estimated decline of 96 % of native tallgrass prairie habitat. Due to the imperiled status of grassland birds, an emphasis has been placed on managing for this particular group throughout the southern mixed-grass prairie region. I investigated the effects of adaptive three-pasture rotational grazing treatments (3ROT) versus traditional season-long grazing treatments (SLG) and other sources of variation on common grassland nesting species at Cheyenne Bottoms Preserve (CBP). I attempted to determine if any significant trends in nest survival could be inferred at the treatment-level scale for grasshopper sparrows (Ammodramus savannarum), western meadowlarks (Sturnella neglect), and eastern meadowlarks (S. magna). In addition to constructing nest survival models, I also measured vegetation variables at nest sites and randomly throughout both treatments. A total of 160 nests were located during the 2012 and 2013 field seasons. For grasshopper sparrows, the resulting final-stage models suggest daily nest survival (DNS) at CBP is linked to litter depth at the nest site and to various factors within the year that were either not measured or non-discernible. For meadowlarks, the resulting final-stage models suggest DNS at CBP is linked to a multitude of measured variables, but most strongly linked to visual obstruction (VOR) at the nest site, mean daily precipitation, and to the specific year. Percent litter coverage and vegetation heights were greater in 3ROT than SLG. Percent bare ground was greater in SLG than 3ROT. Further investigation is needed to better define variables linked to daily nest survival during non-drought conditions and throughout the season at CBP and similar eco-regions within the southern mixed-grass prairie.