1018 The Auk 118(4):1018–1028, 2001 AVIAN NESTING SUCCESS IN FORESTED LANDSCAPES: INFLUENCE OF LANDSCAPE COMPOSITION, STAND AND NEST-PATCH MICROHABITAT, AND BIOTIC INTERACTIONS AMANDA D. RODEWALD 1 AND RICHARD H. YAHNER Intercollege Graduate Degree Program in Ecology and School of Forest Resources, The Pennsylvania State University, University Park, Pennsylvania 16802, USA ABSTRACT.—Although area and isolation effects on avian communities in highly frag- mented landscapes are well known, importance of landscape composition in more forested landscapes remains poorly understood. We determined if the type (agriculture and silvi- culture) and extent (percentage within 1 km radius) of disturbance within forested land- scapes influenced avian nesting success, and then examined if differences in stand-level hab- itat structure, nest-patch microhabitat, distance of nests to habitat edges, brood parasitism rates, and nest-predator abundance were potential underlying mechanisms of observed as- sociations between landscape composition and nesting success. We monitored active song- bird nests (n = 341), surveyed Brown-headed Cowbirds (Molothrus ater) and nest predators, and measured stand-level and nest-patch microhabitat from May–July 1998 and 1999. Each of 10 study sites was located within contiguous mature forest in central Pennsylvania and contained either agricultural or silvicultural disturbances (n = 5 each). Sites of the two land- scape types had similar ranges of disturbance within 1 km (21–55% for agriculture, 18–51% for silviculture). Daily nest survival for all species combined (94.0  0.55 in agriculture and 96.9  0.87 in silviculture) and midstory-canopy nesters (93.8  0.97 in agriculture and 97.4  0.75 in silviculture) were greater within forested landscapes disturbed by silviculturethan by agriculture, but rates did not significantly differ between landscapes for ground nesters (92.2  1.32 in agriculture and 94.6  1.63 in silviculture) or understory nesters (95.4  1.60 in agriculture and 95.0  1.47 in silviculture). Nest survival was not significantly associated with disturbance extent. Rates of brood parasitism were low, with only 11% of nests con- taining cowbird eggs or young. Neither nest fate nor differences in daily nest survival be- tween the two landscape types were explained by variation in brood parasitism rates, stand- level or nest-patch habitat characteristics, or distance of nests to edges. Instead, the lower nest success within forested landscapes disturbed by agriculture was best explained by greater abundances of some avian and small mammalian predators (American Crow [Corvus brachyrhynchos] and squirrels) in those landscapes in one or both years. Results suggest that landscape composition within forested landscapes significantly influences avian nesting success by altering interactions between nest predators and nesting birds. Received 22 March 2000, accepted 7 June 2001. NUMEROUS LANDSCAPE-LEVEL studies of avi- an communities have examined patch area and isolation, finding that diversity, abundance, and nesting success of forest songbirds are re- duced in small forest fragments (Lynch and Whigham 1984, Wilcove 1985, Wilcove and Robinson 1990, Donovan et al. 1995, Hoover et al. 1995, Van Horn et al. 1995, Hagan et al. 1996). However, other landscape characteristics can influence avian community structure and organization as well (Andre´n 1992, Aberg et al. 1995, Coker and Capen 1995, Friesen et al. 1995, 1 Present address: School of Natural Resources, The Ohio State University, 2021 Coffey Road, Colum- bus, Ohio 43210-1085. E-mail: rodewald.1@osu.edu Robinson et al. 1995, Saab 1999). In particular, both amount of habitat disturbance (Askins and Philbrick 1987, Askins et al. 1987, Donovan et al. 1997, Hartley and Hunter 1998) and types of land uses within landscapes (Andre´n 1992, Aberg et al. 1995, Askins 1995, Coker and Ca- pen 1995, Friesen et al. 1995, Kurki and Linden 1995, Huhta et al. 1996, Bayne and Hobson 1997, Saab 1999) can explain variation in avian community structure and nesting success. Our present understanding of mechanisms behind associations between landscape com- position and avian communities is incomplete because multiple underlying factors are seldom examined within single studies. In particular, habitat structure at stand, nest-patch, or both