Area requirements and landscape-level factors influencing shrubland birds

Declines in populations of birds that breed in disturbance-dependent early-successional forest have largely been ascribed to habitat loss. Clearcutting is an efficient and effective means for creating early-successional vegetation; however, negative public perceptions of clearcutting and the small parcel size typical of private forested land in much of the eastern United States make this practice impractical in many situations. Group selection harvests, where groups of adjacent trees are removed from a mature forest matrix, may be more acceptable to the public and could provide habitat for shrubland birds. Although some shrubland bird species that occupy clearcuts are scarce or absent from smaller patches created by group selection, some of these smaller patches support shrubland species of conservation concern. The specific factors affecting shrubland bird occupancy of these smaller patches, such as habitat structure, patch area, and landscape context, are poorly understood. We sampled birds in forest openings ranging 0.02-1.29ha to identify species-specific minimum-area habitat requirements and other factors affecting shrubland birds. We modeled bird occurrence in relation to microhabitat-, patch-, and landscape-level variables using occupancy models. The minimum-area requirements for black-and-white warblers (Mniotilta varia), common yellowthroats (Geothlypis trichas), chestnut-sided warblers (Setophaga pensylvanica), eastern towhees (Pipilo erythrophthalmus), and gray catbirds (Dumetella carolinensis) were 0.23ha, whereas indigo buntings (Passerina cyanea) and prairie warblers (S. discolor) required openings of 0.56ha and 1.11ha, respectively. Notably, prairie warblers were more likely to occur in openings closer to large patches of habitat such as powerline corridors, even if those openings were small in size. We concluded that, despite their inability to support the entire suite of shrubland species, small forest openings can provide habitat for several species of conservation concern if proper attention is given to promoting suitable microhabitat, patch, and landscape characteristics. (c) 2017 The Wildlife Society. In situations where the goal is to accommodate all shrubland bird species in this study, land managers should consider creating forest openings >1.1ha in size; however, if this is not feasible operationally, as is the case for many private forest owners in southern New England, openings 0.23ha in size can still provide habitat for several species of high conservation concern. Managers should consider prioritizing the creation of openings near existing large shrubland patches, which will increase the probability of occurrence of area-sensitive species such as prairie warblers and thus maximize conservation value of management efforts while also minimizing monetary expenses associated with habitat creation.