Nest predation and brood parasitism of two bottomland hardwood forest songbirds
Gannon, Jill J.
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Population declines of forest-interior neotropical migratory songbirds may be linked to a reduction and degradation of breeding habitat that result in increased nest predation and brood parasitism. Bottomland hardwood forests of the southeastern U.S. have undergone severe reductions in both the amount and quality of breeding habitat. The White River NWR is one of the largest remaining contiguous tracts of bottomland hardwood forest in the U.S.; however, songbirds breeding within the Refuge are subjected to high rates of nest predation and parasitism. I used a species-specific, multi-scale approach to investigate the relative importance of habitat characteristics to nest predation and parasitism of two neotropical migrant songbirds, the Acadian Flycatcher (Empidonax virescens) and the Prothonotary Warbler (Protonotaria citrea). Using proportional hazard and logistic regression models, I found that the risk of nest predation and the likelihood of brood parasitism were related to habitat characteristics at multiple spatial scales (micro, macro, and landscape). Water associated with seasonal flooding played an important role in reducing the risk of nest predation at all spatial scales, while a landscape-level factor describing proximity to cowbird foraging sites was strongly associated with increased brood parasitism. Additionally, human-induced disturbances within the forest interior that created edge and open canopy, namely roads and patch cuts, were associated with increased nest predation and parasitism. I conclude that 1) landscape-level management efforts may be most successful in reducing nest predation and brood parasitism within the Refuge and 2) anthropogenic disturbances that may alter the existing flooding pattern of the Refuge should be thoroughly investigated for their potential effects on the nesting success of bottomland forest songbirds.