Diets of plains vizcacha, greater rhea and cattle in Argentina

Abstract

Food habits of plains vizcacha (Lagostomus maximus), greater rhea (Rhea americana) and cattle (Bos taurus) in the Parana? River Delta, Argentina, were studied over 2 years using microhistological analysis of faeces. This was the first study of feeding habits of these herbivores grazing in common in a wetland of Argentina. Poaceae was the main diet component throughout the year for all 3 herbivores, with the exception of spring and summer, when greater rhea consumed a higher proportion of Prosopis nigra (Griseb.) pods. Botanical composition of plains vizcacha and cattle diets was generally similar for the same season but different from that of greater rhea. Panicum milioides Nees., Dichondra microcalyx (Hallier) Fabris. and P. nigra were the most consumed species for vizcacha, while P. nigra, Plantago myosuros Lam., Solanum sp. L., Spilanthes stolonifera (H. et A.) Baker and D. microcalyx dominated the greater rhea diet. The species most consumed by cattle were Luziola peruviana Gmel. and P. milioides. Similarities between the diets of plains vizcacha and cattle seem to support the ranchers' view that vizcachas compete with domestic herbivores for forage. However, high overlap in food habits would result in competition only if forage is scarce. Greater rhea and cattle have different foraging patterns and hunting of greater rhea is not justified solely on the basis of forage competition with cattle.