Resource partitioning between Glossy and White Ibises in a rice field system in southcentral Cuba

Population density, foraging microhabitat and diet composition were analyzed for White Ibis (Eudocimus albus) and Glossy Ibis (Plegadis falcinellus) feeding in the rice field system of ''Sur del Jibaro'' (Sancti Spiritus, Cuba) from May to December 1992. Population density for E. albus ranged from 2.2 individuals ha(-1) in May to 23.2 individuals ha-1 in October, and for P. falcinellus from 1.4 individuals ha(-1) in August to 217 individuals ha(-1) in October. Both species of ibis shared the same main foraging microhabitats, except in October when, coinciding with their highest population densities, they segregated their foraging grounds. White Ibis foraged mainly in recently muddied fields where, owing to the action of machinery, an abundance for crabs and aquatic insects were available; Glossy Ibis concentrated in flooded fields where mature rice was shedding its grain. Overall, these species segregated on diet: White Ibis fed on crabs (48%), aquatic insects (37%) and fish (15%); the Glossy Ibis fed on rice grains (58%), aquatic insects (26%) and crabs (15%). A quantitative assessment of the granivorous feeding habits of Glossy Ibis is presented in this paper for the first time. We suggest that Glossy Ibis may be primarily a plant eater in certain situations, shifting to an animal-food based diet during the breeding season.