Attacks on adult females with infants by non-resident males in the François langur.

Infanticide by males is a common phenomenon in mammals, especially primates, as lactation lasts much longer than gestation in many species. Usually, infanticidal episodes occur soon after group takeovers, and are traditionally considered a male reproductive strategy (i.e., support the sexual selection hypothesis, Hrdy, 1974). To verify the validity of this conception, we observed one group of Francois' langurs in the Nonggang Nature Reserve, China, between August 2003 and July 2004. During the study period, a Francois' langur female with the youngest infant in the group was attacked three times by immigrating males, and later disappeared by the third day after the final attack. We suggest that these attacks on the female-infant dyad represent infanticide attempts by males, and may be the cause of the adult female and her infant's disappearance. Presumably, that female dispersed with her infant to avoid infanticide and was not killed. Though these observations do not completely verify the sexual selection hypothesis, they are not inconsistent with it.