Tenure related changes in wild Thomas's langurs II: Loud calls

In this paper, we investigate how the number and context of male loud calls of Thomas's langurs (Presbytis thomasi) change over a male's tenure, in re lation to changes in the intensity of male mate competition and relative ma le strength. We also investigate how the calls' impact on the behavior of r eceivers varies over tenure phases. Thomas's langurs live in one-male multi -female groups; only males produce loud calls; both males and females dispe rse from their natal groups; female secondary dispersal is also common, and infanticide occurs. The life-span of a group is, as a rule, restricted to the tenure of its reproductive male (median tenure length is 72 months). Ma le tenure in bisexual groups was divided into three phases: the early phase (no infants yet), the stable middle phase, and the late phase (last year). Because AMBs remained after all females had left a male, they were treated as a fourth phase. We hypothesised that the tendency to answer another male's calls decreases with distance because a male will invest less when answering becomes less r elevant. The tendency to respond to a loud call by a? extra-group male inde ed decreased with distance, which suggests that males invested less in (cos tly) calling behavior when the chance of an interaction with that male was low. Extra-group males seemed to recognise males of new groups: they did no t discriminate between medium and far distances in answering calls from (re latively unfamiliar) early tenure males. We further hypothesised that an increase in male mate competition would res ult in mon call bouts per day and a higher tendency to answer calls, which was not found. Males with a relatively low strength were expected to keep s ignalling their presence, but because this low strength includes a higher r isk for females and infants, we expected females to avoid loud calling extr a-group males. Males with a declining strength continued to signal their pr esence, as was expected, but they did reduce participation in dawn call bou ts, which might be a particularly sensitive measure of their decreased stre ngth. Extra-group males answered calls by males during their late tenure ph ase more often at medium and far distances, which shows that males recognis ed calls from late tenure males. Females' avoidance of calling extra-group males remained constant during the early and middle phase but increased dur ing the late tenure phase, as was expected. AMB males clearly avoided males from bisexual groups: they never participated in dawn call bouts, they rar ely started or answered calls and they travelled away from calling males.;A MB males only answered a call bout in the case of a between-group conflict, when their position was already known. Hence, in Thomas's langurs, loud ca ll behavior influenced male mate competition, and it varied in relation to changes in relative male strength.