Although competition between females is a fundamental aspect of the evolution of mammalian societies, studies investigating which ecological factors might explain variation in the intensity of female conflict have been limited. Here, we focus on one of the most intense forms of competition, the killing of conspecific offspring. Our study shows that infanticide by females occurs in species in which breeding females have high reproductive rates, where the potential to monopolize resources can directly increase their current reproductive success. Female infanticide is also more likely to occur where females compete for burrows or helpers. While infanticide risk is higher in group-living than in solitary species, it does not seem to have led to changes in the social system. We will discuss other morphological or physiological adaptations in females that might have reduced the risk of infanticide.