Abstract Accurate knowledge of the functional response of predators to prey density is essential for understanding food web dynamics, to parameterize mechanistic models of animal responses to environmental change, and for designing appropriate conservation measures. Greater flamingos ( P hoenicopterus roseus ), a flagship species of M editerranean wetlands, primarily feed on A rtemias ( A rtemia spp .) in commercial salt pans, an industry which may collapse for economic reasons. Flamingos also feed on alternative prey such as C hironomid larvae (e.g., C hironomid spp .) and rice seeds ( O ryza sativa ). However, the profitability of these food items for flamingos remains unknown. We determined the functional responses of flamingos feeding on A rtemias, C hironomids, or rice. Experiments were conducted on 11 captive flamingos. For each food item, we offered different ranges of food densities, up to 13 times natural abundance. Video footage allowed estimating intake rates. Contrary to theoretical predictions for filter feeders, intake rates did not increase linearly with increasing food density (type I). Intake rates rather increased asymptotically with increasing food density (type II) or followed a sigmoid shape (type III). Hence, flamingos were not able to ingest food in direct proportion to their abundance, possibly because of unique bill structure resulting in limited filtering capabilities. Overall, flamingos foraged more efficiently on A rtemias . When feeding on C hironomids, birds had lower instantaneous rates of food discovery and required more time to extract food from the sediment and ingest it, than when filtering A rtemias from the water column. However, feeding on rice was energetically more profitable for flamingos than feeding on A rtemias or C hironomids, explaining their attraction for rice fields. Crucially, we found that food densities required for flamingos to reach asymptotic intake rates are rarely met under natural conditions. This allows us to predict an immediate negative effect of any decrease in prey density upon flamingo foraging performance.