Abstract
1 Anthropogenic alteration of landscapes can affect avian nest success by influencing the abundance, distribution, and behavior of predators. Understanding avian nest predation risk necessitates understanding how landscapes affect predator distribution and behavior.2 From a sample of 463 nests of 17 songbird species, we evaluated how landscape features (distance to forest edge, unpaved roads, and power lines) influenced daily nest survival. We also used video cameras to identify nest predators at 137 nest predation events and evaluated how landscape features influenced predator identity. Finally, we determined the abundance and distribution of several of the principal predators using surveys and radiotelemetry.3 Distance to power lines was the best predictor of predator identity: predation by brown-headed cowbirds (Molothrus ater), corvids (Corvus sp. and Cyanocitta cristata), racers (Coluber constrictor), and coachwhips (Masticophis flagellum) increased with proximity to power lines, whereas predation by rat snakes (Elaphe obsoleta) and raptors decreased. In some cases, predator density may reliably indicate nest predation risk because racers, corvids, and cowbirds frequently used power line right-of-ways.4 Of five bird species with enough nests to analyze individually, daily nest survival of only indigo buntings (Passerina cyanea) decreased with proximity to power lines, despite predation by most predators at our site being positively associated with power lines. For all nesting species combined, distance to unpaved road was the model that most influenced daily nest survival. This pattern is likely a consequence of rat snakes, the locally dominant nest predator (28% of predation events), rarely using power lines and associated areas. Instead, rat snakes were frequently associated with road edges, indicating that not all edges are functionally similar.5 Our results suggest that interactions between predators and landscape features are likely to be specific to both the local predators and landscape. Thus, predicting how anthropogenic changes to landscapes affect nesting birds requires that we know more about how landscape changes affect the behavior of nest predators and which nest predators are locally important.
Highlights
Anthropogenic habitat alteration can have pervasive effects on wildlife beyond just loss of habitat
Ecology and Evolution published by John Wiley & Sons Ltd
The top-ranked model from our set of six candidate models influencing daily nest survival rate was the distance to nearest unpaved road (Table 1)
Summary
Anthropogenic habitat alteration can have pervasive effects on wildlife beyond just loss of habitat. The quality of remaining habitat may decline due to an increase in edge habitat or the isolation of remaining patches (Andren 1994). These changes often cause shifts in wildlife species richness, density, or distribution within a landscape (Chalfoun et al 2002). Installation of linear corridors such as roads and utility right-of-ways may result in relatively little habitat loss, but negatively affect wildlife by creating extensive edge habitat, by inserting early-successional habitat into a forested matrix (Rich et al 1994), or by modifying the behavior of predators.
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