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We examined the numerical and spatial responses of Geoffroy's cats (Oncifelis geoffroyi) to a prey decline in central Argentina between April 2002 and November 2003. The 2nd year of the study coincided with a severe drought. Relative abundance of brown hares (Lepus europaeus) declined from 5.6 individuals/10 km during the predrought period to about 0.6 individuals/10 km during the drought. Small-rodent biomass also showed the lowest level for the study area during the drought of 2002-2003 (134.5 g/ha). During the predrought and drought periods, 3 male and 1 female, and 1 male and 9 female Geoffroy's cats, respectively, were radiotagged and monitored. Home ranges for males of the predrought period averaged 202.8 ha [+ or -] 156.8 SD and that of the single female was 27.3 ha. During the drought period, 4 females occupied an average home range of 254.9 [+ or -] 254.1 ha, and the home-range size of the single predrought female increased by a factor of 2. No obvious change in mean daily distance traveled between the 2 periods was observed. Geoffroy's cats predominantly used habitats of dense cover during the predrought period, but they became more habitat generalists during the drought. Recruitment of juveniles was only recorded during the predrought period, and all monitored Geofffoy's cats dispersed or died of starvation after the prey decline. Consequently, density of Geoffroy's cats dropped from 2.9 individuals/10 [km.sup.2] before the drought to 0.3 individuals/10 [km.sup.2], probably because of food scarcity. This is the 1st study to examine the spatial ecology of a small wild cat species under nutritional (energetic) stress in South America. Key words: Argentina, drought, Geoffroy's cat, home range, Monte, Oncifelis geoffroyi, prey decline, radiotelemetry, space use