Landscape and local effects on avian habitat use and breeding success in bottomland hardwood forests of the Mississippi Alluvial Valley
Hazler, Kirsten Rebecca
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During the breeding season, nest predation and brood parasitism are critical factors influencing songbirds’ reproductive success. Therefore, minimizing risk should be an important factor in selecting breeding habitat, whether at the scale of the patch, territory, or nest site. I examined these ideas in a landscape and local study of avian habitat selection, density, and breeding success in bottomland hardwood forests of the Mississippi Alluvial Valley. At the local scale, I investigated how perceived risk from red-bellied woodpeckers (Melanerpes carolinus, nest predators) and brown-headed cowbirds (Molothrus ater, brood parasites) affected Acadian flycatcher (Empidonax virescens) territory settlement. Woodpecker risk was higher on vacant territories in only one of the two years, and apparent woodpecker avoidance appeared to be mediated indirectly through habitat preferences. Cowbird risk was higher on vacant territories in both years, and avoidance appeared to be mediated both by indirect habitat effects as well as a direct behavioral response. I investigated landscape context and local vegetation effects on densities of Acadian flycatchers and four other migratory species, as well as on relative abundance of red-bellied woodpeckers and brown-headed cowbirds. In addition, for flycatchers I investigated the factors influencing nest survival and incidence of brood parasitism. Nest survival increased with increasing forest cover (and hence, decreasing agriculture) in the surrounding landscape. Acadian flycatchers were particulary sensitive to interior forest openings from patch cuts and other disturbances. We found that incidence of brood parasitism decreased with increasing distance from forest disturbances, and that population density decreased with increasing forest disturbance in the surrounding landscape. This is consistent with our finding that brown-headed cowbirds were positively associated with early successional forest cover in the landscape, including interior forest openings. We do not know how much influence red-bellied woodpeckers have as nest predators, but we did find that, at the landscape scale, flycatcher population density was negatively related to woodpecker abundance, after controlling for landscape context and vegetation effects.