DIET AND FOOD RESOURCE PARTITIONING AMONG SIX IBIS SPECIES IN THE VENEZUELAN LLANOS

Abstract

This work is the first one to provide simultaneous information on the diet of all six ibis species inhabiting the Venezuelan Llanos. For this we analyzed gizzard contents of birds collected in 1979-1982 (between 59 and 11 per species). The seasonality of the rainfall has a great influence on the prey eaten by the ibises (diet overlap between dry and wet season varied between 0.07 and 0.45 depending on the species). Main prey (in percent of prey number) for Scarlet/White ibis (Eudocimus ruber) were: Coleoptera (73%), Diptera (12%) and Heteroptera (6%) in the dry season, and Coleoptera (82%) and Odonata (9%) in the wet season. For Barefaced Ibis (Phimosus infuscatus): Coleoptera (72%) and Ephemeroptera (20%) in the dry season, and Oligochaeta (65%), Ephemeroptera (19%) and Coleoptera (14%) in the wet season. For Glossy Ibis (Plegadis falcinellus): Spinicaudata (79%), Coleoptera (18%) and plant material (18% of the total volume of food items) in the dry season, and Coleoptera (51%), Decapoda (28%), Odonata 10%) and Heteroptera (8%) in the wet season. For Sharptailed Ibis (Cercibis oxycerca): Pisces (30%), Lepidoptera (28%), Coleoptera (27%) and Orthoptera (6%) in the dry season, and Coleoptera (35%), Orthoptera (33%) and Oligochaeta (29%) in the wet season. For Buffnecked Ibis (Theristicus caudatus): Coleoptera (43%), Orthoptera (42%), Arachnida (7%) and Lepidoptera (6%) in the dry season, and Coleoptera (56%) and Orthoptera (35%) in the wet season. For Green Ibis (Messimbrinibis cayennensis): Coleoptera (75%), Gastropoda (7%) and Orthoptera (6%) in the dry season, without data in the wet season. The diet overlap between pairs of species showed low to medium values (0.13-0.44 in dry season, 0.03-0.60 in wet season). These data support the idea that the coexistence of these species is largely facilitated by food resource partitioning.