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The mara is a near threatened Caviomorph, endemic to Argentina. Studies on feeding ecology allow assessment of the dietary adaptability of maras to habitat changes. The mara diet and food availability on two sampling sites, belonging to distinct landscapes of Northern Patagonia, were estimated using microhistological analysis and point-quadrat transects, over four seasons, and besides during an extended drought. Significant differences were detected by Kruskall-Wallis ANOVA, feeding selection by the chi(2) test, and dietary preferences by Bailey’s confidence interval. Grasses dominated food availability, with Panicum and Poa as major species, followed by shrubs and scarce forbs. Plant cover and forbs increased in spring and summer. The drought caused a strong decrease in plant cover and proportion of grasses. Maras ate all grass species, most forbs and several shrubs. Grasses dominated the diet, with Poa and Panicum being the major species, supplemented by the shrubs Lycium and Prosopis. Maras ate more grasses and forbs in spring and summer, and shrubs in autumn and winter. More shrubs and forbs, and less grasses, were eaten during the drought. Plant categories were used selectively only in autumn and winter, and in the drought period, with preference for shrubs and avoidance of grasses. Bromus, Foci, Plantago and Prosopis were preferred, and Panicum avoided. The mara qualified as a grazer but shifted to a mixed feeder during the drought. Dolichotis patagonum shared habitats with several big and medium-sized herbivores and showed the highest dietary similarities with plain vizcachas, brown hares and horses. Protective measures for natural habitats are needed, given that increasing impacts on food resources and habitat quality could be threats to the survival of maras and other wild vertebrates in Northern Patagonia. (C) 2009 Deutsche Gesellschaft far Saugetierkunde. Published by Elsevier Gmbh. All rights reserved.