Chief U.S. District Judge Charles Haden has scheduled a hearing for Wednesday on a request for an injunction to halt the operation.
Last week, lawyers for the Conservancy and a group of coalfield residents filed a copy of the Fish and Wildlife Service's study with Haden.
"The forested valleys in the study area appear to support a diverse wildlife community," the report says. "During the field investigations, tracks of white-tailed deer and wild boar and feathers of wild turkey were observed. In addition, gray squirrel, chipmunk, ruffed grouse and several songbirds were either seen or heard by the investigators.
"If this forest were allowed to mature, more mast would be produced, further enhancing its values for wildlife," it says. "The perennial streams and riparian borders in the valley bottoms add to habitat complexity, and provide a reliable supply of water for wildlife."
However, the report concluded, "If the [mountaintop removal mine] is constructed as proposed, and the typical mining revegetation plan is followed after mining, the existing steep, forest interior will be replaced by gently rolling grasslands with small, scattered stands of trees and shrubs.
"The forested valley habitats enhanced by the perennial streams as a water supply, were found to be capable of supporting high wildlife species diversity," the report said. "This site is not likely to support many of these species, particularly migrant forest interior birds, following mining."