Introduction

It is now widely accepted that infanticide by males has affected important features of primate social organization by selecting for various social counterstrategies of females (Hrdy 1979; Smuts & Smuts 1993; van Schaik 1996; Treves & Chapman 1996; see various chapters in this book). One of these possible female counterstrategies is female secondary transfer (Marsh 1979b; Sterck 1997; Sterck & Korstjens, Chapter 13). Female transfer decisions are expected to be strongly influenced by the identity of the male with whom a female associates. Secondary transfer is expected only where female relationships are relatively weak because it means the break-up of associations and coalitions, at least temporarily. Hence, given the predominance of female philopatry in primates, only a small number of species is expected to show this behavior. Thomas's langurs (Presbytis thomasi) are one of the few species known to show female secondary transfer related to infanticide avoidance. Females leave when infants have died or when they are old and independent enough to be left behind (Sterck 1997; Steenbeek 1999a). This makes the Thomas's langur an excellent choice for investigating the possible influence of infanticide on social relationships, since in species like this female choice in relation to male characteristics and strategies will be most manifest.

Species with regular female secondary transfer are of particular interest, because where the group contains only a single male, female emigration may terminate a group's lifespan.