Browsing by Author "Christopher E. Moorman, Committee Member"

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    The effects of patch shape and connectivity on nest site selection and reproductive success of the Indigo Bunting
    (2004-03-01) Weldon, Aimee Jean; Nick M. Haddad, Committee Chair; Christopher E. Moorman, Committee Member; Theodore R. Simons, Committee Member
    Habitat fragmentation and its associated effects have been blamed for the recent population declines of many Neotropical migratory bird species. Increased predation and parasitism resulting from edge-related effects have been implicated for poor nesting success in many studies, mostly of forest interior species. However, little attention has been devoted to disturbance-dependent birds. In this study, I examine how patch shape and connectivity in fragmented landscapes affects the reproductive success of disturbance-dependent bird species, specifically the Indigo Bunting (Passerina cyanea). I conducted my study in a landscape-scale experimental system of similar-area habitat patches that differed in connectivity and in shape. Shapes differed between edgy and rectangular forms, where edgy patches contained 50% more edge than rectangular patches. I tested whether edgy patches function as ecological traps for species with strong edge preferences, by leading them to select dangerous habitats. Indigo Buntings preferentially selected edgy patches over rectangular patches, but experienced significantly lower reproductive success in edgy patches early in the season. Although predation pressure intensified in rectangular patches late in the season, seasonal fecundity was still significantly lower in edgy patches, providing the first empirical evidence that edges can function as ecological traps for Indigo Buntings. A second objective of my study was to evaluate the efficacy of conservation corridors for disturbance-dependent bird species. Conservation corridors have become a popular strategy to preserve biodiversity and promote gene flow in fragmented landscapes, but corridors may also have negative consequences. I tested the hypothesis that corridors can increase nest predation risk in connected patches relative to unconnected patches. Nest predation rates increased significantly in connected patches compared to unconnected rectangular patches, but were similar between connected patches and unconnected edgy patches. This suggests that the increase in predator activity in connected patches is largely attributable to edge effects incurred through the addition of a corridor. This is the first landscape-scale study to experimentally demonstrate the potential negative effects of conservation corridors.
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    Mammalian Nest Predators Respond to Greenway Width, Habitat Structure, and Landscape Context
    (2003-08-31) Novotny, Kristen Elise; Nick M. Haddad, Committee Member; George R. Hess, Committee Chair; Christopher E. Moorman, Committee Member
    Birds of conservation concern breed in suburban greenways, yet abundant populations of mammals that depredate bird nests may compromise nest success. We evaluated how three factors influenced total mammalian nest predator abundance and individual species abundance in greenways of Raleigh and Cary, North Carolina, USA: 1) the width of the forested corridor containing the greenway, 2) the type of land-use adjacent to the forested corridor, and 3) the habitat structure within the greenway. Forest corridor width and adjacent land-use were measured for 34 greenway segments using aerial photographs. Several measures of habitat structure within the greenway were collected in the field during September 2002, including trail width and surface type, stream width, 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 season. Mammalian nest predators were significantly more abundant in greenways within narrower forested corridors. Mammalian nest predator abundance was lowest in greenways with forested corridors wider than 200 meters, and continued to decline as forest corridor width increased. Most of the species we identified are known to inhabit edge habitat, which was present throughout greenways within narrow forested corridors. We found no relationship between categorical measures of land-use context (low-density residential, high-density residential, office/institutional) and mammalian nest predator abundance. Specific landscape features adjacent to the greenway, however, did affect mammalian nest predator abundance. Greenways adjacent to landscapes with fewer buildings had a higher abundance of total mammalian nest predators, and the abundance of individual species varied with the amount of canopy, lawn, and pavement in the adjacent landscape. The habitat structure of the greenway was correlated with the mammalian nest predator community, yet no habitat structure variables were significant in all species models. Segments with wider trails had a higher abundance of mammalian nest predators, as did sampling areas located closer to trails and with more mature forest. Raccoon abundance was higher in segments with wider trails, and lower in segments near parking lots or roads, playing fields, and backyards. Opossum abundance was higher in segments near water and trails. Gray squirrel abundance was higher in segments near backyards. Domestic cat abundance was higher in segments with more mature forest, near parking lots or roads, and lower further from streams. To reduce the risk of avian nest predation by mammals, greenways should be designed with wider forest corridors and narrower trails, particularly natural dirt footpaths instead of paved or cleared trails. Additional features of greenways are likely to increase the abundance of particular species. Greenway forest corridors with more paved areas in the adjacent landscape are likely to have higher abundances of rats and mice, and domestic cats if the paved area borders the greenway. Increasing lawn in the adjacent landscape is likely to increase opossum abundance in greenways. Greenways that border backyards are likely to have a higher abundance of gray squirrels. Increasing canopy cover in the adjacent landscape will positively influence raccoon abundance, as will increasing mature forest within the greenway habitat for total mammalian nest predators and domestic cats. Many of these vegetative characteristics also create habitat for birds of conservation concern. Management of these features must balance reduction of predator communities with promotion of desired bird communities.