Although the effects of habitat edges on avian nesting success are well documented for forest ecosystems and for forest-interior species, there is almost no evidence for nonforest, agriculturally dominated landscapes, namely for the matrix of shrubby wetlands and agricultural land. In 1995–1998 I searched for and monitored nests of the Scarlet Rosefinch (Carpodacus erythrinus) in pristine patches of shrubby wet meadow to evaluate the generality of the “edge effect on nest predation” hypothesis. Predation was the major cause of nest failure, accounting for 92.3% of total nest losses. Microhabitat features of the nest sites were not related to proximity to agricultural edges. The model best describing variation in daily nest-survival rates (DSRs) included nest concealment and distance to agricultural edge. Nest survivorship for the entire nesting period was estimated at 41% (1,143 exposure days, n = 79 nests) for edge nests (<100 m from an edge) and 83% (1,831 exposure days, n = 96) for interior nests, respectively. The DSRs were also consistently higher in large than in small wetland patches. Using habitat-specific demographic parameters, I found that per-capita annual productivity was 66.3% higher in core areas than in edge areas (4.14 and 2.49 fledglings, respectively). Three key components of annual reproductive success—brood size, nest success, and renesting rate—contributed unevenly to variation in site-specific annual per-capita productivity, only the latter two being important predictors. The results indicate that edge habitats may not be perceived as suboptimal by breeding individuals, despite high rates of brood loss there.
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Vol. 121 • No. 2