We studied a system in which 2 desert rodent species coexist through temporal partitioning. Previous research suggests that the common spiny mouse (Acomys cahirinus) competitively forces the golden spiny mouse (A. russatus) into diurnal activity, but the mechanism driving this separation is not entirely understood. To test whether aggression is the driving force in this exclusion, we analyzed interactions between pairs of these 2 species. In contrast with our working hypothesis, the golden spiny mouse was more aggressive as reflected in its significantly more frequent chasing and biting behaviors. These results suggest that aggressive interference does not explain the temporal partitioning between these species. Other factors such as foraging efficiency, antipredator avoidance, water conservation, or productivity may account for the shift of golden spiny mice into diurnal activity.