Optimal Shrub Density for Bird Habitat in the Midwestern United States

摘要

Shrubs play a key role as bird habitat in eastern North America and are associated with a group of songbirds that are in sharp decline in the Midwest region, U.S.A. Savanna restoration throughout the region is a key priority for vegetation managers, and a priority goal is often to clear the understory of woody species encroachment, including shrubs. However, while the benefit of maintaining a shrub layer in restored savanna has been noted by wildlife managers, the degree to which native shrubs should be retained has not yet been quantified. In this study, I measured songbird occurrence in sites that met the criteria of savanna physiognomy and that have shrub cover ranging from 10 to ≥75%. The results indicated that the highest overall species richness and richness of species conservation concern occurred when shrub cover was ≤35%. This observation suggests that shrub cover in the range of 10-35% may be adequate to conserve declining shrub dependent bird species, while also meeting the objective of opening the understory desired by savanna restoration practitioners.