Background/Question/Methods Grassland birds are the fastest declining avian guild in North America due to habitat loss and alteration. These declines require that available grasslands be managed in a manner advantageous to the birds’ productivity. The National Park Service wishes to allocate their resources for management to properties that have the capacity to benefit regional grassland bird populations the most. We assessed the grassland bird community structure, obligate grassland bird nest success, and vegetation heterogeneity at three Great Plains National Park Service properties of varying size (small, medium, and large) at different latitudes, in the summer of 2008. We hypothesized that avian diversity and evenness would decrease with park size and latitude, and that the most homogeneous vegetation structure would support the highest nest success.

Results/Conclusions  Both diversity and evenness were lowest at the largest park (4,300 ha), highest at the medium sized park (114 ha), and in between for the smallest park (65 ha). Both diversity and evenness increased with latitude. Grassland bird richness was greatest at the northern most park and lowest at the middle latitude park. The largest park had the most homogeneous vegetation structure and the smallest park had the most heterogeneity in structure. Estimated nest success was higher at the smallest park and nest predation was higher at the large, homogeneous park. Brown-headed Cowbird densities were similar between parks. In our study, smaller parks at higher latitudes had higher diversity, evenness, and nest survival, contrary to expectations.