ABSTRACT
How do new males benefit from infanticide? The average tenure of male coalitions in prides is only 24 months before they are ousted or move on voluntarily to new prides (Pusey and Packer, 1987a) (Figure 2). Because cubs are vulnerable to death following takeovers until they are at least 9 months old (Figure 1), males only have a good chance of fathering surviving cubs if they inseminate females soon after they have taken over a pride. After females have given birth to surviving cubs, they do not come into estrus again until their cubs are at least 18 months old; the average interbirth interval between surviving cubs is 24 months (Pusey and Packer, 1987a) (Figure 2). However, if they lose their cubs, females resume mating activity within days or weeks, regardless of season (Schaller, 1972; Bertram, 1975; Packer and Pusey, 1983a,b), and they mate with which ever males are resident in the pride. Females that lose small cubs (less than 4 months of age) at a takeover conceive again about 4.4 months after the loss (Packer and Pusey, 1983b). In calculating the precise gains males make by killing small cubs rather than waiting for females to come into estrus, it is necessary to consider both females whose dependent cubs died in other circumstances than at a takeover and those whose cubs survived, because cub mortality is high even in the absence of takeovers (Packer et al., 1988). Considering all these females, median postpartum amenorrhea in the absence of a takeover is 11.3 months, and conception occurs about one month later (Packer and Pusey, 1983b). Thus, by killing small cubs when they first take over a pride, males sire cubs about 8 months sooner, on average, than they would if they spared the cubs of the previous males (Packer and Pusey, 1984). Besides speeding up the females' reproduction, another possible advantage of infanticide to males is that the cubs will not provide feeding competition for younger cubs fathered by the males. Bertram (1975) provided evidence that the presence of older cubs depressed the survival of younger cubs within the same cohort, but we have not been able to confirm this between successive cohorts (Pusey and Packer, 1987a).
