Breeding bird populations in relation to the vegetation structure of abandoned contour mines in Southwest Virginia
Twelve study areas on abandoned contour mines in southwest Virginia were surveyed to investigate relationships between breeding bird population parameters and structural aspects of the disturbed area vegetation. The territorial mapping method was employed to census bird populations. The number of breeding species, number of breeding pairs, bird species diversity, and number of observed species (breeding or visiting) were determined for each disturbed area, the marginal undisturbed forest, and each total study area (marginal and disturbed areas combined). Vegetation was sampled within units of similar vegetation on each disturbed area; 17 vegetation parameters were recorded for each unit. These were weighted by the size of each vegetation unit and averaged for each disturbed area. Linear and multiple regressions of each population variable were performed on 51 vegetation and site-factor variables.
Bird population parameters of the disturbed and total study areas showed positive relationships with several aspects of disturbed area revegetation. However, among forested orphan mines, decreases in bird populations were observed when canopy closure apparently affected a reduction in understory vegetation. Bird populations of the marginal areas decreased with the reforestation of the disturbed areas, apparently reflecting a decrease in the edge effect. Several sets of equations for population parameters of the disturbed and total study areas are presented for use in habitat evaluation.
Relationships revealed for bird population parameters of the disturbed and total study areas suggest that reclamation efforts should strive to achieve a high degree of vegetative cover, increase the amount of ground layer vegetation, and provide for the future development of higher vegetational strata. These vegetational features should be introduced in a manner which will augment existing vegetational heterogeneity.