Grassland vegetation and bird abundances on reclaimed midwestern coal mines

摘要

Reclamation of surface coal mines in the midwestern United States has produced large grasslands, which support both obligate and facultative grassland birds. We sought to characterize vegetation and determine whether birds breeding in these habitals responded to vegetation as they do in other kinds of grasslands. We measured vegetation characteristics on 9 Indiana mine grasslands and related those measures to abundance or occurrence of 6 common bird species. Eurasian grasses such is tall fescue (Festuca arundinacea) and smooth brome (Bromus inermis), prominent in seed mixtures planted decades earlier, comprised 64% of canopy cover. Forb cover averaged 27%, with as much cover by native invaders such as goldenrod (Solidago spp,) as by legumes planted during reclamation. Despite a superficial appearance of homogeneity, mine grassland vegetation varied sufficiently to affect local abundances of birds. Abundances of 3 ubiquitous species varied and were correlated with at least 1 characteristic; red-winged blackbirds (Agelaius phoeniceus) were negatively associated with percent cover by litter and by grass, whereas eastern meadowlarks (Stumella magna) and grasshopper sparrows (Ammodramus savannarum) were negatively associated with vegetation density. No variables were associated with occurrence of dickcissels (Spiza americana) or common yellowthroats (Geothlypis trichas), although yellowthroat abundance at the occupied sites appeared to increase with greater vegetation density. Occurrence of Henslow's sparrow (Ammodramus henslowii) was positively associated with 5 variables, including percent cover by litter and grass, Blackbirds, dickcissels, and yellowthroats did not differ in abundance between grass- and forb-dominated sites, whereas Henslow's and grasshopper sparrows and meadowlarks were more common on the former. Thus, obligate grassland birds benefited from the present dominance of non-native grasses over forbs on reclaimed mines. Despite a lack of native vegetation and their artificial nature, mine grasslands supported a typical array of midwestern grassland bird species that differ in specific vegetation preferences, showing patterns similar to those observed in natural and agricultural grasslands.