Reclaimed coal mine grasslands and their significance for Henslow's sparrows in the American Midwest

Present methods of surface coal-mine reclamation in the Midwest produce lar ge grasslands, some of which exceed 2,000 ha in extent. Total "mine grassla nd" production in southwestern Indiana alone is well in excess of 70 square miles (180 km(2)). Our work in 19 reclaimed coal mines in southwestern Ind iana indicates that mine grasslands harbor many Henslow's Sparrows (Ammodra mus henslowii). We base that conclusion on point-count and line-transect su rveys that yielded between 200-300 singing male Henslow's Sparrows during t he 1997 and 1998 breeding seasons. Those survey results imply an uncorrecte d population density of similar to0.10 males per hectare, and a corrected d ensity of similar to0.16 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 gras slands of southwestern Indiana. Small-scale vegetational surveys suggest th at much of the within-mine variation in Henslow's Sparrow abundance reflect s local vegetative structure, with males preferring sites typically associa ted with that species of bird: tall, dense grass-dominated vegetation with a substantial litter layer. Management for this kind of vegetative structur e could greatly increase the number of Henslow's Sparrows inhabiting reclai med mines. Midwestern mine grasslands could play a significant role in stab ilizing the populations of Henslow's Sparrows and other grassland birds.