Greater prairie‐chicken nest survival and changes in vegetation structure and composition with conservation grazing

Abstract Conservation grazing is a management practice to maintain or restore prairie vegetation conditions. The application of conservation grazing in highly fragmented grasslands, such as Minnesota's tallgrass prairie, has received far less study than larger western grasslands of the Great Plains. Because only 1% of tallgrass prairie remains in Minnesota, informed application of this management practice is necessary to ensure area‐sensitive wildlife, like the greater prairie‐chicken ( Tympanuchus cupido pinnatus ), are not adversely affected by management. We studied conservation grazing at a range of stocking rates representative of those used by wildlife managers in northwestern Minnesota to determine its influence on vegetation composition and structure and greater prairie‐chicken nest survival. Each of the 10 study sites had 3 pastures of similar size located in proximity to each other, for which we assigned early grazing (May–June), late grazing (July–August), and no grazing (control) in the grazing treatment year. We located nests by nest‐searching each of the 3 pastures in pre‐grazing (2021), grazing (2022), and post‐grazing (2023) treatment years and by following radio‐marked females to nests. Visual obstruction readings of vegetation within pastures indicated early and late grazing had a significant short‐term effect with a mean height reduction of 11.6 cm between August of the year before grazing (2021, 29.5 ± [SD] 17.9 cm) and August of the grazing year (2022, = 17.9 ± 8.9 cm). In 2022, we observed an increase in new grass (22.4%) and bare ground (22%) and a reduction in residual grass (33%) and litter (31%) cover in grazed pastures in August. During the nesting season in the post‐grazing year, we saw positive effects of grazing on vegetation for all cover types except bare ground, with new grass increasing 3.6%. However, the beneficial vegetation changes dissipated by August of the post‐grazing year. Mean nest survival was 0.565 (SE = 0.114), 0.315 (SE = 0.066), and 0.797 (SE = 0.129) in pre‐grazing, grazing, and post‐grazing years, respectively, with lowest survival during the grazing year when there was also extensive flooding. The nest survival model including year outperformed a model with an interaction between grazing timing and year, suggesting that interannual variability in weather conditions was more influential than grazing activity. However, the magnitude of the reduction in nest survival in the grazing year was 67.1% in the early‐grazed pasture, compared to 27.5% and 37.3% in control and late pastures, respectively. Additional studies during years with less interannual variation are recommended to resolve possible treatment effects that might have been difficult to detect in the midst of such large interannual variability.