Ecological strategies successfully predict the effects of river floodplain rehabilitation on breeding birds

To improve the ecological functioning of riverine ecosystems, large-scale floodplain rehabilitation has been carried out in the RhineMeuse Delta since the 1990s. This paper evaluates changes in abundance of 93 breeding bird species over a period of 10 years in response to rehabilitation, by comparing population changes in 75 rehabilitated sites with 124 non-rehabilitated reference sites. Such quantitative, multi-species, large-scale and long-term evaluations of floodplain rehabilitation on biodiversity are still scarce, particularly studies that focus on the terrestrial component. We try to understand the effects by relating population trends to ecological and life-history traits and strategies of breeding birds. More specifically, we try to answer the question whether rehabilitation of vegetation succession or hydro-geomorphological river processes is the key driver behind recent population changes in rehabilitated sites. Populations of 35 species have significantly performed better in rehabilitated sites compared to non-rehabilitated floodplains, whereas only 8 have responded negatively to rehabilitation. Differences in effects between species are best explained by the trait selection of nest location. Reproductive investment and migratory behaviour were less strong predictors. Based on these three traits we defined eight life-history strategies that successfully captured a substantial amount of variation in rehabilitation effects. We conclude that spontaneous vegetation succession and initial excavations are currently more important drivers of population changes than rehabilitation of hydrodynamics. The latter are strongly constrained by river regulation. If rehabilitation of hydro-geomorphological processes remains incomplete in future, artificial cyclic floodplain rejuvenation will be necessary for sustainable conservation of characteristic river birds. Copyright (C) 2010 John Wiley & Sons, Ltd.