Replacement female house sparrows regularly commit infanticide: gaining time or signaling status?

Although the killing of unrelated young (usually designed as infanticide) has been typically considered a male behavior, recent research has shown that females may commit infanticide even more frequently than do males. In rodents and primates, female infanticide represents a strategy associated to competition for resources or infant exploitation, but little is known about the causes and reproductive consequences of the killing of conspecifics by females in other vertebrates. In the present article, I focus on infanticide committed by females that replace mates of territorial males in a population of the house sparrow. I show that (1) replacement females regularly committed infanticide, (2) experienced females committed infanticide more frequently than did novel females and tended to select polygynous males to take over their nests, and (3) laying date and reproductive success after a territory takeover did not differ between infanticidal and noninfanticidal females. These results seem to indicate that infanticide has not evolved in females because of the short-term reproductive benefits it accrues to the perpetrator. I suggest that the killing of unrelated young by females relates to dominance status among potential female breeders and that this behavior benefits the perpetrators in terms of mate selection. Copyright 2004.female-female competition; female infanticide; female replacement; house sparrows; sexual selection