Abstract # 2740 Event # 98:

Scheduled for Sunday, September 20, 2009 11:30 AM-11:40 AM: Session 8 (Shell Room) Oral Presentation


M. E. Hopkins1 and K. Milton2
1University of Texas, Austin, Dept. of Anthropology, 1 University Station C3200, Austin, TX 78727, USA, 2Dept. of Environmental Science, Policy, & Management, University of California, Berkeley, CA 94720, USA

Over 33 species of primates produce long distance vocalizations (‘long-calls’), with hypothesized functions ranging from competition for females to resource defense. The howler monkey long-call, specifically, has been hypothesized to mediate costly inter-group conflict either through mutual avoidance or the reciprocation of movements between neighbors. Yet, observational studies examining group response to the naturally occurring calls of known neighbors have found little evidence of a consistent spatial response. This year-long study on Barro Colorado Island, Panama examined the directional movements of two mantled howler monkey groups immediately following the naturally occurring long calls of six known neighbor groups. Like previous observational studies, this study found that when all howls were treated equally, groups were as likely to travel towards a neighboring group’s howl as they were to travel away from it or to the left/right [Group1: n=545, Χ2(3)=2.0, p>0.57; Group2: n=707, Χ2(3)=3.8, p>0.27]. However, once interaction histories between neighboring groups, the location of the howling group, and levels of resource availability were taken into account, a multinomial logit model could correctly classify a group’s spatial response (i.e. travel towards/away/neither) in the majority of cases [likelihood ratio test: 19.87, p<0.01]. Our results highlight the complexity present in inter-group vocal interactions and stress the importance of considering behavioral, spatial, and environmental factors in evaluations of the functional significance of primate vocalizations.