Examined were 5 years of data on the reproduction of a semifree-ranging population of Barbary macaques (Macaca sylvanus). In this seasonally breeding species – birth season: mid-March to beginning of August – primiparous 4-year-old females gave birth significantly later in the year than older primiparous and multiparous females, respectively. Multiparous females without an infant from the preceding season gave birth significantly earlier than females who had raised an infant. 88.4% of birth intervals were approximately 1 year, 11.6% about 2 years. Infant loss did not influence the length of the interbirth interval, but after the birth of the next surviving infant the interval was significantly longer. The interval following the 1st infant was significantly longer than after subsequent infants. After the birth of daughters primiparous females had markedly longer birth intervals than after the birth of sons. Infant mortality was 9.1%. Neonatal mortality was influenced by rank and parity of the mother and sex of the infant. Allomothering and aggression by older group members are thought to be the main causes of infant mortality. Female reproduction rates were not dependent on rank. High-ranking females, however, bore their 1st infant significantly earlier than low-ranking females. Low-ranking females had more daughters than sons, in high-ranking females the reverse was found. Differences from findings of other species are discussed with regard to differences in social organization and the reproductive strategies resulting from them.

Information on infant killing by males is reviewed and extended by personal communications and observations. Most cases of infant killing reported occurred during periods when a new alpha male was establishing himself and during arranged encounters of strangers or unfamiliar individuals in captivity. There seem to be no specific releasing stimuli for infant killing, but rather the lack of familiarity between male and females, their nonacceptance of him in the whole set of roles tied to the alpha status, and his special motivational condition as new alpha lead him to a state, in which attacks on infants may result. Infant killing is considered to have a selection advantage by increasing one’s own reproduction success while reducing the one of other males.