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We explore the implications of an often overlooked fact in community restoration: most species, in real or synthetic communities, are infrequent or rare, a phenomenon we call “inherent rarity.” Whether from long‐term interactions of many factors affecting birth, death, and establishment within natural communities, or from short‐term interactions of recently created communities, species abundance distributions are roughly lognormal or even more attenuated. The greater the predisturbance species diversity of remnants or the planting diversity of restorations, and the smaller the area of a habitat patch, the more likely a large proportion of species will exist in populations so small that they are acutely or chronically vulnerable to local extinction. We suggest that habitat fragmentation will inevitably favor plants and animals that are highly mobile, early successional species, including many exotic weeds among plants, or species that are historically organized as metapopulations that happen to be common enough to function as such. We further explore rationales for countering the effects of inherent rarity, including connectivity from buffers, corridors, and stepping stones, and dominance suppression from seasonally appropriate mowing, grazing, or fire.

The Lower Kihansi Hydropower Project in southern Tanzania caused the diversion of the Kihansi River from the Kihansi Gorge in the year 2000. By sampling the understorey avifauna prior to diversion, we examined (i) whether the adjacent Udagaje Gorge was an adequate control for observations in the Kihansi Gorge; (ii) which species of conservation interest occurred; and, (iii) which season best suited annual monitoring. Species composition and capture rates at three and two elevational transects in the Kihansi Gorge and Udagaje Gorge, respectively, confirmed that Udagaje had a comparable avifaunal assemblage to Kihansi. The cold season was most appropriate for population monitoring because >2 times more individuals were captured in the cold than hot season at both gorges, and at least four altitudinal migrants were present in the cold but not hot season. Post-diversion sampling revealed that only the Upper Kihansi transect suffered a significant decrease in number of individuals, a result that was driven largely by a decline in the Little Greenbul, Andropadus virens. This transect is closest to the Kihansi waterfall and associated spray zone which were lost after river diversion. Lack of differences in bird communities at other transects after diversion illustrates that early post-diversion effects on birds are probably concentrated near the base of the main falls. Together with studies of other biota in Kihansi, we propose that longterm monitoring is necessary to understand the factors that regulate changes in species composition of this threatened forest site.

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Summary 1.We provided equal feeding opportunities for bark-foraging bird species across seasons, cleared and uncleared woody understories, edge-to-interior habitat and tree diameters in a deciduous oak forest in north-eastern Illinois, USA, to determine habitat preferences of these bird species. We determined habitat preferences by quantifying patch-use intensity. 2. Patch-use intensity was greater in the breeding season than in the non-breeding season, and in interior than in edge habitat. In addition, however, we found interactions among the habitat variables. For instance, these bird species showed significant preferences for foraging in woodland interior habitat and on large diameter trees in the breeding season, but not in the non-breeding season. 3. Foraging preferences were further affected by understorey clearing, with preference for interior over edge habitat reversed in the cleared habitat in the non-breeding season. This effect may reflect unintended consequences of topography, an uncontrolled factor outside the experiment protocol. 4. Overall, the results suggest that patch-use results from the response of the bird species to effects of vegetation variation from edge to interior habitat on both microclimate and predation risk. Those effects of vegetation may disappear or diminish when understorey vegetation is removed or reduced.