Many bird species nest in precarious, unpredictable locations to decrease the risk of predation. Although it is likely that many species have adapted behaviors to deal with stochastic habitats, there is currently limited evidence of plastic behavior increasing avian fecundity in the wild. Virginia Rails (Rallus limicola) and Soras (Porzana carolina) live in the littoral zones of wetlands that experience high hydrologic variability. During the summers of 2010 and 2011, we tested for the effects of hydrology and behavioral plasticity on the survival of Virginia Rail (n = 75) and Sora (n = 22) nests across 10 wetlands in Maine, USA. We identified the best predictors of both (1) nesting success at individual nests and (2) mean nesting success at the site level, using logistic-exposure models and an information-theoretic approach. Daily nesting survival was 98% for both species, and apparent nest survival was 31 of 85 nests, or 63.5%. Ninety percent of all nesting failures was from predation. Hydrology had a positive effect on nesting survival, and deeper, more variable water levels increased both individual nesting survival and mean site-level nest survival. Both species added material to their nests throughout the season in response to water-level increases, and we found that this behavioral plasticity had a positive effect on nesting survival. We caution that more variable water depths than those observed during our 2 yr of study could lead to increases in flood-related nest loss, because these birds require a delicate balance: the water must be deep enough to deter predators, yet shallow enough that they can build up their nests to prevent flooding during rain events. More information is needed on the extent of this behavior across marsh birds and other bird species.
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Vol. 132 • No. 1