Managers of protected areas are under increasing pressure to measure their effectiveness in conserving native biological diversity in ways that are scientifically sound, practical, and comparable among protected areas over time. The Nature Conservancy and its partners have developed a "Measures of Success" framework with four core components: (1) identifying a limited number of focal conservation targets, (2) identifying key ecological attributes for these targets, (3) identifying an acceptable range of variation for each attribute as measured by properly selected indicators, and (4) rating target status based on whether or not the target's key attributes are within their acceptable ranges of variation. A target cannot be considered "conserved" if any of its key ecological attributes exceeds its acceptable range of variation. The framework provides a rigorous basis not only for measuring success but for setting conservation objectives, assessing threats to biodiversity, identifying monitoring and research needs, and communicating management information to nonspecialists.

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Many species of Nearctic landbirds exhibit behavioral plasticity during migration, presumably to compensate for energetic demands of migratory flight. At Block Island, Rhode Island, a northern temperate site, I quantified the extent of one form of behavioral plasticity in Nearctic landbirds: dietary expansion from breeding season insectivory to high levels of frugivory during autumn. I also measured changes in energetic condition of migrants using recapture methods and diurnal regressions of mass change. Based on analyses of 1,568 fecal samples collected from 1993-1995, frugivory during migration was frequent within many species, extensive within individual birds, and widespread among taxa. Migratory species ranged from strict insectivory in the Winter Wren (Troglodytes troglodytes) to 96% fruit by volume in the fecal samples of Rose-breasted Grosbeaks (Pheucticus ludovicianus). Nine of 17 recaptured species demonstrated mass gains between first and last recapture. Only the Red-eyed Vireo (Vireo olivaceus) gained significant mass within a single day, suggesting that the site was suitable for migratory mass gain if a species remained longer than one day. Highly omnivorous species, with greater than one-third of the diet as fruit, gained significantly more mass while on Block Island than did strict insectivores, i.e., species with less than one-third of the diet as fruit. Insectivorous species on average declined in energetic condition during stopover. The extent of frugivory for a species was positively correlated with average change in energetic condition and fat score per day, suggesting that frugivory allowed species to gain mass more efficiently and extensively than exclusive insectivory. I conclude that frugivory in Nearctic landbirds is far more extensive during migration than previously thought, and that dietary plasticity may be an adaptation to energetic demands of migratory flights.

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