Landscape Ecology 15: 131–143, 2000. © 2000 Kluwer Academic Publishers. Printed in the Netherlands. 131 Effects of landscape structure on nest predation in roadsides of a midwestern agroecosystem: a multiscale analysis Timothy M. Bergin 1* , Louis B. Best 1 , Kathryn E. Freemark 2 & Kenneth J. Koehler 3 1 Department of Animal Ecology, Iowa State University, Ames IA 50011, USA 2 National Wildlife Research Centre, Environment Canada, 100 Gamelin Blvd., Hull, Quebec, Canada K1A 0H3 3 Department of Statistics, Iowa State University, Ames, IA 50011, USA ( * author for correspondence: e-mail: tbergin@iastate.edu) (Received 10 November 1997; Revised 1 December 1998; Accepted 17 May 1999) Key words: Agricultural landscapes, artificial nests, landscape structure, multiscale analysis, nest predation, roadsides, spatial scale Abstract Nest predation is an important cause of mortality for many bird species, especially in grassland ecosystems where generalist predators have responded positively to human disturbance and landscape fragmentation. Our study evaluated the influence of the composition and configuration of the surrounding landscape on nest predation. Transects consisting of 10 artificial ground nests each were set up in 136 roadsides in six watersheds in south- central Iowa. Nest predation on individual roadside transects ranged from 0 to 100% and averaged 23%. The relationship of landscape structure within spatially-nested landscapes surrounding each roadside transect (within 200, 400, 800, 1200, and 1600 m of the transect line) to nest predation was evaluated by using multiple regression and canonical correlation analyses. The results of this multiscale landscape analysis demonstrated that predation on ground nests was affected by the surrounding landscape mosaic and that nest predators with different-sized home ranges and habitat affinities responded to landscapes in different ways. In general, wooded habitats were associated with greater nest predation, whereas herbaceous habitats (except alfalfa/pasture) either were associated with less nest predation or were not important. Different landscape variables were important at different spatial scales. Whereas some block-cover habitats such as woodland were important at all scales, others such as rowcrops and alfalfa/pasture were important at large scales. Some strip-cover habitats such as gravel roads and paved roads were important at small scales, but others such as wooded roadsides were important at all all scales. Most landscape metrics (e.g., mean patch size and edge density) were important at large scales. Our study demonstrated that the relationships between landscape structure and predator assemblages are complex, thus making efforts to enhance avian productivity in agricultural landscapes a difficult management goal. Introduction The intensification and specialization of modern agri- culture have dramatically altered the habitat compo- sition and spatial configuration of agricultural land- scapes in temperate North America (Herkert 1994; Warner 1994; Freemark 1995; Rodenhouse et al. 1995). The fragmentation and disturbance of grass- lands by agriculture have created a landscape mosaic of large blocks of cropland, small patches of remnant prairie or other grassed habitats, and an interconnected network of narrow (< 20 m), often linear, strip-cover habitats such as roadsides (Warner 1994; Rodenhouse et al. 1995; Koford and Best 1996). These changes in landscape structure have adversely affected avian species diversity and abundance in agroecosystems (Herkert 1994; Freemark 1995; Rodenhouse et al. 1995) and contributed to population declines of grass- land birds over much of North America (Robbins et al. 1986; Askins 1995; Robinson 1996). Research in agroecosystems is important if we are to manage, en- hance, or restore the ecological features of agricultural