A study was undertaken to determine and compare the grazing ecology of goats, red deer and South American camelids when pastured on three contrasting vegetation types typical of hill and upland ecosystems in Scotland: an established sown sward (Lolium perenne dominated); an indigenous grassland (Nardus stricta dominated); and a dwarf-shrub community (Calluna vulgaris dominated). Plots at each site were grazed in sequence with data collected during one spring (May/June) and two summer (August/September) experimental sessions. For each period at each site plant species composition, canopy structure and herbage biomass were characterized. Samples of the diet selected by up to five mature castrated goats, red deer and guanacos fistulated at the oesophagus were used to establish diet composition and in vitro digestibility of the diet. Herbage intake and diet digestibility of an additional five intact animals of each species were determined using n-alkane faecal markers. Total grazing time was estimated using vibracorders and bite rate data collected by observation. The influence of vegetation type and season on the diet composition and ingestive behaviour of each species was evaluated. Between species comparisons on each vegetation type were also made. Differences in selectivity for and against vegetation components indicate that guanacos are principally grazers while goats and red deer are intermediate feeders. On the Lolium sward the goats and red deer selected green leaf of both monocotyledonous and dicotyledonous plants whereas the guanacos selected only graminoids. On the Nardus community the main dietary component for all three animal species was broad-leaved grasses selected from the species-rich intertussock areas. On the dwarf-shrub community there was strong selection for and against graminoid species and Calluna vulgaris respectively, with the dominant species of plant only making a substantial contribution to the red deer diet. Where differences between estimates of diet digestibility were identified the digestibility of material consumed by each species of animal on the sown sward was higher than that from either indigenous community; and the digestibility of material selected from the indigenous grassland was higher than that from the dwarf-shrub community.