La prédation du Flamant rose Phoenicopterus ruber roseus par le Goéland leucophée Larus cachinnans en Camargue

Abstract

Yellow-legged herring gulls prey on the Greater Flamingo breeding colony in the Camargue, taking both eggs and chicks. They kill young chicks in their nest and flightless young forming large aggregates («crèches»). To rob nests the Yellow-legged herring gulls have developped a technique which forces the brooding flamingo to stand up. Once standing the brooding bird no longer defends its nest and the gull can take its content. Two or more gulls can cooperate when trying to catch larger chicks in a crèche. Such an attack causes young in the crèche to clump together and this may deter predation. Of the attacks observed 42 % were successful and 7 % unsuccessful, in spite of the perseverence of the predators. Fifty one percent were only brief interactions, the predators not pursuing their attack. Predatory episodes were most numerous during late afternoon until dusk, and between the end of May and the beginning of June when all nests held eggs or small chicks. As their size increased chicks became progressively more difficult to overcome. All predators were adult gulls nesting on the «Flamingo Island» itself. Attempts by some immature and juvenile birds were scarce. Marginal and late flamingo nests were more vulnerable to predation than those located in the center of the colony. In the Camargue, the Yellow-legged herring gull breed three weeks before the flamingo. The adaptive value of this time-lag between the breeding seasons of the two species is discussed. The total number of eggs and chicks taken by the gulls is estimated to be at least 11 % of the eggs laid (without taking into account second clutches). Furthermore 32 % of the flamingo eggs (exclusive second clutches) were lost for other reasons, but eaten by the gulls afterwards. Flamingo eggs and chicks can account for up to 40 % of the food intake of the 14 pairs of Yellow-legged herring gulls breeding on the «Flamingo Island». Flamingo predation by Yellow-legged herring gulls is known from the Camargue and Lake Rezaiyeh (Iran) only. Flamingos are very vulnerable to predation but the size of the colony and the close synchronisation of the breeding cycle may reduce its impact. Under present controlled conditions the Yellow-legged herring gulls do not appear to exert much influence on the population dynamics of the Camargue flamingos.