Diet preference and density of the Greater Rhea (Rhea americana) in grasslands of the Flooding Pampa, Argentina

Abstract

The Greater Rhea (Rhea americana) has been greatly affected by habitat alteration and hunting. Density of rheas was estimated by monthly surveys along transects from June 1996 to November 1997 in 760 ha of coastal grasslands in the Flooding Pampa, Buenos Aires Province, Argentina. Fresh feces and vegetation samples were collected in spring 1996, and in winter and spring 1997 to study diet and resource selection. Feces were macroscopically processed, and the vegetal fraction was prepared for micro histological analysis. Vegetation was sampled in quadrants, separated by species and dried to obtain the percentage of dry weight to estimate availability. Mean density was 0.22 ± 0.04 rheas/ha. Dicots were always preferred in relation to their availability in the grassland, and monocots were not preferred in neither of the two spring seasons studied. Monocots were consumed more frequently than dicots in winter. Legumes were preferred in both spring seasons, with Black Medic (Medicago lupulina) the most consumed species. Perennial Ryegrass (Lolium perenne) was the most represented monocot, but it was always consumed in proportions similar to its availability. Grasses growing in warm seasons were never preferred. The diet of Greater Rheas in these grasslands was generalist and almost completely herbivorous, showing preference for dicots, mainly legumes. Rheas were more selective in spring, when the availability of the vegetation was higher than in winter.