eligmodontia morgani is one of the most abundant endemic species of arid patagonian steppe. most previous studies have focused on systematics and taxonomy and ecological information on this species is scarce. the objectives of this study were to estimate population parameters for e. morgani in the patagonian steppe ecoregion and to compare them to parameters available for this species in another environment. data were collected from february 2003 through october 2004. abundances ranged from 12±1.85 to 71±6.67, with residents comprising 39% of the population. the sex ratio was female biased and age classes resulted in juveniles body mass ≤11 g, subadults between 13-15 g, and adults ≥17g. the breeding season lasted from august to march. the home range sizes were 659.72±90.55 m2 for females and 439.58±114.54 m2 for males. the comparison of present results with those obtained in the subandean district within the patagonian steppe ecoregion showed similar home range sizes and residency but a different proportion of e. morgani in the total number of rodent captures, trap success, and sex ratio. the ability of this species to occupy diverse arid environments of patagonia may evidence a significant ecological niche breadth.