04. Population Trends of Breeding Grassland Birds at Midewin National Tallgrass Prairie, 1985–2015

We use data from ongoing bird monitoring programs to assess long-term population trends at Midewin National Tallgrass Prairie in northeastern Illinois. Midewin is the nation’s first National Tallgrass Prairie and was established in 1996 on the site of the former Joliet Army Ammunition Plant. Annual bird monitoring began at the site in the early 1980s when it was discovered that the pastures and hayfields maintained by the Army contained significant grassland bird populations. Ninety-four species of breeding birds were recorded at the site between 2009 and 2015, including large populations of several grasslandobligate birds including dickcissel (Spiza americana), eastern meadowlark (Sturnella magna), grasshopper sparrow (Ammodramus savannarum), bobolink (Dolichonyx oryzivorus), and Henslow’s sparrow (Ammodramus henslowii). Trend analyses showed that populations of bobolink, grasshopper sparrow, and savannah sparrow (Passerculus sandwichensis) were stable on the site between 1985 and 2015, whereas dickcissel and Henslow’s sparrow showed significant population increases during this interval. Three species declined significantly between 1985 and 2015: eastern meadowlark, upland sandpiper (Bartramia longicauda), and vesper sparrow (Pooecetes gramineus). The stable population trends for bobolink, grasshopper sparrow, and savannah sparrow contrast sharply with statewide and regional trends for these species, which show large population declines. The recent introduction of bison to the site may help provide the habitat structure needed to maintain large grassland bird populations at the site.