Mammalian nest predators respond to greenway width, landscape context and habitat structure

Abstract

Birds of conservation concern breed in suburban greenways, yet abundant populations of mammals that depredate bird nests might reduce nest success. We evaluated how three factors influenced the abundance of mammalian nest predators in thirty-four 300-m long forested greenway segments in Raleigh and Cary, North Carolina, USA: (1) the width of the forested corridor containing the greenway, (2) the land-use adjacent to the forested corridor, and (3) the habitat structure within the greenway. Forest corridor width and adjacent land-use were measured using aerial photographs. Attributes of adjacent land use included categorical measures of development intensity (low-density residential, high-density residential, office/institutional), and the proportions of forest canopy, grass, buildings, and pavement. Several measures of habitat structure within the greenway were collected in the field, including trail width and surface type, and percentage of mature forest. We measured the relative abundance of mammalian nest predators with scent-station transects, operated for five nights during the 2002 breeding bird season. Total abundance of mammalian nest predators increased significantly as forest corridor width decreased. We found no relationship between categorical measures of land-use and total abundance of mammalian nest predators. Specific attributes of the landscape adjacent to the greenway, however, did have an effect. Greenways adjacent to landscapes with fewer buildings had a higher abundance of mammalian nest predators. The abundance of individual species varied with the amount of canopy, lawn, and pavement in the adjacent landscape. Some measures of habitat structure of greenways also were correlated with the abundance of mammalian nest predators. Greenway segments with wider trails had a higher abundance of mammalian nest predators, as did segments with a higher percentage of mature forest. No habitat structure variables were significant for all species. To reduce the overall risk of avian nest predation by mammals, forested greenways should be designed with wider forest corridors and narrower, unpaved trails. Some greenway characteristics that favor high-nest predator populations also favor birds of conservation concern. Similarly, some characteristics correlated with lower predator occurrence are also correlated with lower abundance of birds of conservation concern. Thus, management of greenways and the surrounding landscape must balance reduction of predator communities with the promotion of desired bird communities and other conservation goals.