Effects of group-selection opening size on breeding bird habitat use in a bottomland forest

An increase in timber removals from southern bottomland forests of the Unit ed States has been predicted, warranting investigations of the effects of s ilvicultural alternatives on avian breeding habitat. We;studied the effects of creating group-selection openings (man-made canopy gaps) of various siz es on breeding bird habitat use in a bottomland hardwood forest in the Uppe r Coastal Plain of South Carolina, USA. We used spot mapping and mist netti ng to estimate bird abundance at 0.06-, 0.13-. 0.26-, and 0.5-ha gap's and at uncut control areas during the 1996, 1997, and 1998 breeding seasons (I May-1 August). There were significant increases in the number of species ma pped (P = 0.0001) and netted (P = 0.0001) with successive increases in gap size. The greatest number of total spot-map detections (P = 0.0002) and mis t net captures (P = 0.0004) also occurred in and around the large gaps. The se patterns were the result of increased use of larger gaps by field-edge s pecies, primarily Brown-headed Cowbird (Molothrus ater), Common Yellow-thro at (Geothlypis trichas), and Indigo Bunting (Passerina cyanea), and some fo rest-edge species, such as White-eyed Vireo (Vireo griseus) and Northern Pa rula (Parula americana). Conversely, Acadian Flycatcher (Empidonax virescen s) Was less abundant in and adjacent to gaps. Because there were few differ ences in vegetation among gaps of different sizes, it is likely that birds that were detected more frequently in and adjacent to larger gaps selected those gaps based on other factors correlated with size. Creation of 0.5-ha group-selection openings in southern bottomland forests should provide bree ding habitat for some field-edge species in gaps and habitat for forest-int erior species and canopy-dwelling forest-edge species between gaps. provide d that sufficient mature forest is maintained.