USE OF TRILL VOCALIZATIONS TO COORDINATE TROOP MOVEMENT AMONG WHITE-FACED CAPUCHINS - A 2ND FIELD-TEST

The white-faced capuchin, Cebus capucinus, employed a specialized voca lization, the trill, to coordinate troop movement at La Selva, an Atla ntic wet-forest study site in Costa Rica. We analyse the contexts in w hich this intra-group vocalization was emitted, including responses el icited from other group members. A cumulative 26.6 hours of continuous samples and 3,314 spectrograms (including 1,295 trills) were analysed from a study troop with 16 focal subjects. These results generally co rroborate the conclusions of a comparable field study of T white-faced capuchins at Santa Rosa, a Pacific coast dry-forest site in Costa Ric a(BOINSKI, 1993, Amer. J. Primatol. 30, p. 85-100). At both sites, (1) trills were closely associated with the initiation of movement by a s tationary troop in a specific direction. (2) Trills were emitted at a much higher rate in the leading edge of a travelling troop than in fol lowing positions. (3) Individuals often reinforced the efforts of othe r troop members to coordinate troop movement. (4) Lack of consensus am ong troop members over the travel route was evident. (5) In rare insta nces trills were employed in tactical maneuvers suggestive of intentio nality and the ability to anticipate behavioural effects. Differences in the usage of trills at these two sites were also detected. (1) At L a Selva all troop members, with the exception of infants, used trills in the coordination of troop movement, whereas at Santa Rosa marked ag e, sex and rank distinctions in the extent of participation were appar ent. (2) Capuchins at Santa Rosa altered the trajectory of travelling troops with trills, even reversing directions, but not at La Selva. Th ese disparities may follow from differences between the sites in the e xtent of visual and auditory contact typical among troop members, soci al structure, susceptibility to predation, and possible genetic variat ion.