By Lance McNew, Wildlife Research Biologist, U.S. Geological Survey
Birds that rely on grassland habitat to breed are the most imperiled bunch in North America. Horizon-to-horizon grassland habitats are a thing of the past in most areas where it used to be common, and, as a result, grassland birds are in trouble. It is no surprise then that the large, relatively intact tallgrass prairie of Kansas is often considered a stronghold for grassland birds, including greater prairie-chickens. Unfortunately, spring surveys conducted by the Kansas Department of Wildlife, Parks, and Tourism suggest declining populations in eastern Kansas over the last 30 years. So why is a grassland obligate and indicator species for unfragmented prairie declining in the largest remaining tallgrass prairie left in North America?
To answer this question, my colleagues at Kansas State University and I conducted a suite of studies to assess how variability in rangeland management regimes and grassland fragmentation influence prairie-chicken demography, population viability, and habitat use. We found that variation in reproductive success was related to variability in rangeland management practices - nest success in areas managed with annual spring burning and intensive early stocking (IESB) was dismal (<10%) and significantly lower than in grasslands managed with longer fire return intervals and lower stocking densities (20-30%). Nest success was maximized when vertical nesting cover (i.e., grass and forb height) was 15-30 inches tall. In contrast, variability in annual survival of adult prairie-chickens was driven by grassland fragmentation with the highest survival in unfragmented prairie. (McNew et al. 2012a).
In a separate study evaluating how experimental rangeland management practices have affected prairie-chickens at Konza prairie over the last 28 years, we found declining prairie-chicken occupancy at Konza despite the land protections in place. Interactions between fire and grazing influenced long-term colonization and site abandonment probabilities. Woody plant expansion at sites with long fire-return intervals limited colonization, especially on grazed sites, while long-term fire frequency interacted with grazing regime to influence whether previously occupied sites were abandoned (McNew et al. 2012b). While increasing our knowledge of how fire frequency and grazing impact grassland ecology, the experimental grassland management protocols at Konza have negatively impacted prairie-chickens by suppressing fire and encouraging woody encroachment.
I’m guessing you are not surprised. The results of these and our other studies generally quantify what any wildlife biologist worth her/his salt has speculated for years: large-scale annual burning and intensive early grazing of tallgrass prairie in Kansas is just as harmful to prairie-chickens as no burning. The result of too much fire and intensive grazing is abysmal nest success due to inadequate nest cover. The result of too little disturbance is tallgrass prairie too rank to be suitable for nesting and brood-rearing or too woody to be used at all. Prairie-chicken-minded managers of tallgrass prairie in Kansas should take heart. In contrast to populations in isolated and fragmented tallgrass prairie systems where large-scale prairie restoration is required for population recovery, populations in eastern Kansas lack only fire and grazing regimes that facilitate, rather than hinder, nest and brood survival. Prairie-chickens evolved with fire and grazing in tallgrass ecosystems, and our research indicates that land management practices that mimic historically patchy fire and grazing regimes have the potential to curb population declines.
McNew, L.B., A.J. Gregory, S.M. Wisely, and B.K. Sandercock. 2012a. Demography of greater prairie-chickens: regional variation in vital rates, sensitivity values, and population dynamics. Journal of Wildlife Management 76: 987-1000.
McNew, L.B., T.J. Prebyl, and B.K. Sandercock. 2012b. Effects of rangeland management on the site occupancy dynamics of prairie-chickens in a protected prairie preserve. Journal of Wildlife Management 76: 38-47.