Counts of coots (Fulica atra), an herbivorous bird species, and pochards (Aythya ferina), an invertebrate feeder species, were realised during two years in two adjoining gravel pits, presenting the same physical factors, of the Garonne river floodplain (South-West France). At the same time, we analysed the composition and density of fish, invertebrate and macrophyte communities in each gravel pit. Inverse proportion of fish and birds were noticed in the two gravel pits. Taking into account that environmental and physical factors are the same between the two gravel pits, we can conclude that direct and indirect competition between fish and waterbirds should be at the origin of these differences. Benthic fish species such as carp (Cyprinus carpio), silver bream (Blicca bjoerkna) and crucian carp (Carassius carassius) are the main waterbirds competitors on benthic invertebrates and on macrophytes. Patterns of fish community management on gravel pits are discussed as a useful technique for increase waterbird numbers and diversity.
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