Robb A. Bajema’s research while affiliated with Aquinas College - Michigan and other places

Present methods of surface coal-mine reclamation in the Midwest produce large grasslands, some of which exceed 2,000 ha in extent. Total “mine grassland” production in southwestern Indiana alone is well in excess of 70 square miles (180 km2). Our work in 19 reclaimed coal mines in southwestern Indiana indicates that mine grasslands harbor many Henslow's Sparrows (Ammodramus henslowii). We base that conclusion on point-count and line-transect surveys that yielded between 200–300 singing male Henslow's Sparrows during the 1997 and 1998 breeding seasons. Those survey results imply an uncorrected population density of 0.10 males per hectare, and a corrected density of 0.16 males per hectare (correcting for undetected males). Extrapolating this corrected density to total habitat coverage suggests an overall population of a few thousand Henslow's Sparrows in the mine grasslands of southwestern Indiana. Small-scale vegetational surveys suggest that much of the within-mine variation in Henslow's Sparrow abundance reflects local vegetative structure, with males preferring sites typically associated with that species of bird: tall, dense grass-dominated vegetation with a substantial litter layer. Management for this kind of vegetative structure could greatly increase the number of Henslow's Sparrows inhabiting reclaimed mines. Midwestern mine grasslands could play a significant role in stabilizing the populations of Henslow's Sparrows and other grassland birds.

Henslow's sparrow (Ammodramus henslowii) abundance, measured as average number of males at point counts, varied within and among reclaimed mine grasslands of southwestern Indiana. The 19 mine grasslands studied range from about 100 to 3200 ha and vary in landscape structure and composition both within the mines and in relation to the surrounding area. Nevertheless, few landscape-level attributes of mine grasslands were related to Henslow's sparrow abundance. Landscape composition (e.g., percent forest or grassland cover), in particular, had a negligible effect on Henslow's sparrow abundance. Neither habitat patch size nor shape had a significant effect on Henslow's sparrow abundance, but these birds tended to avoid habitat edges. Variation in Henslow's sparrow abundance was, however, influenced by the composition and structure of local vegetation. The relative “landscape insensitivity” of Henslow's sparrows probably reflects the large area of mine grasslands rather than a true lack of landscape-sensitivity in this species.

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 habitats 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 as 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 (Sturnella 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.

We studied the breeding bird communities of 19 reclaimed surface coal-mine grasslands in southwestern Indiana in 1997–1998, using roadside point counts and off-road transects. The mine grasslands in this study were large, ranging from 110 to 3180 ha in area (median, 590 ha). Although dominated by a few Eurasian grass species, they supported diverse bird communities in which grassland-dependent species were prominent along with grassland-associated and successional scrub species. The mean abundances of species (relative to one another) on roadside and off-road counts were positively correlated. Red-winged Blackbirds (Agelaius phoeniceus), Eastern Meadowlarks (Sturnella magna), and Grasshopper Sparrows (Ammodramus savannarum) were present at >90% of point count locations. Other common species, in descending order, included Dickcissels (Spiza americana), Common Yellowthroats (Geothlypis trichas), Killdeers (Charadrius vociferus), Indigo Buntings (Passerina cyanea), Henslow's Sparrows (Ammodramus henslowii), Field Sparrows (Spizella pusilla), and Song Sparrows (Melospiza melodia). Brown-headed Cowbirds (Molothrus ater) were rare, as were seven grassland-dependent species that were near the edges of their geographic distributions.

Present methods of surface coal-mine reclamation in the Midwest produce large grasslands, some of which exceed 2,000 ha in extent. Total “mine grassland” production in southwestern Indiana alone is well in excess of 70 square miles (180 km2). Our work in 19 reclaimed coal mines in southwestern Indiana indicates that mine grasslands harbor many Henslow's Sparrows (Ammodramus henslowii). We base that conclusion on point-count and line-transect surveys that yielded between 200–300 singing male Henslow's Sparrows during the 1997 and 1998 breeding seasons. Those survey results imply an uncorrected population density of ∼0.10 males per hectare, and a corrected density of ∼0.16 males per hectare (correcting for undetected males). Extrapolating this corrected density to total habitat coverage suggests an overall population of a few thousand Henslow's Sparrows in the mine grasslands of southwestern Indiana. Small-scale vegetational surveys suggest that much of the within-mine variation in Henslow's Sparrow abundance reflects local vegetative structure, with males preferring sites typically associated with that species of bird: tall, dense grass-dominated vegetation with a substantial litter layer. Management for this kind of vegetative structure could greatly increase the number of Henslow's Sparrows inhabiting reclaimed mines. Midwestern mine grasslands could play a significant role in stabilizing the populations of Henslow's Sparrows and other grassland birds.