Who is coordinating collective movements in black and gold howler monkeys?
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ORIGINAL ARTICLE
Who is coordinating collective movements in black and gold howler monkeys? Vanina A. Ferna´ndez • Martı´n Kowalewski Gabriel E. Zunino
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Received: 2 May 2012 / Accepted: 15 January 2013 / Published online: 3 February 2013 Ó Japan Monkey Centre and Springer Japan 2013
Abstract Decisions about when and where to travel are likely to have a strong influence on the feeding, ecology, and foraging strategies of individual primates living in a cohesive social group. Specifically, given differences in age, sex, reproductive status, or social dominance, particular group members may benefit from remaining at their present location while others may benefit from traveling to another area of their range to feed or rest. In this study, we present data on movement coordination in two groups of wild black and gold howler monkeys inhabiting Isla Brasilera (278 200 S and 588 400 W) in northern Argentina. We examine how factors such as sex, age, reproductive status, and dominance affect patterns of group movement coordination at feeding or resting sites, and in the context of intergroup encounters. Two groups were followed five days a month from sunrise to sunset during June to November 2004. Using focal and scan sampling techniques, we recorded 262 group displacements, the identity of the individual initiating and leading displacement, and the identity of the first individual to arrive at feeding, resting, or intergroup encounter sites. We found that overall age was the only factor that influenced group coordination: adults led more often (94.5 %) than immature individuals (5.5 %) in both groups. We did not find differences among adults. However, we found that males lead more often than females at intergroup encounters, consistent with the maleV. A. Ferna´ndez (&) M. Kowalewski G. E. Zunino Estacio´n Biolo´gica Corrientes-Museo Argentino de Ciencias Naturales, Av. Angel Gallardo 470, C1405DJR Buenos Aires, Argentina e-mail: [email protected] G. E. Zunino Instituto del Conurbano, Universidad Nacional de General Sarmiento, Los Polvorines, Argentina
mate defense hypothesis. The distributed leadership pattern among adults observed in this study may suggest that adult individuals make equally shared consensus decisions. This pattern should be further examined using this individuallevel approach in other populations of black and gold howlers, other species of howlers, and in other atelines in which within-group social tolerance is the rule rather than the exception. Keywords Leadership Group coordination Collective behavior Decision making Alouatta caraya
Introduction Individuals that live in cohesive social units in which the group members remain in visual or auditory contact need to reach a certain level of group consensus about their displacements (Boinski 2000, Jacobs 2010). In this ‘‘consensus decision,’’ group members choose between two or more mutually exclusive actions with the specific aim of reaching an agreement (Conradt and Roper 2003, 2005). In this regards, a collective movement is defined by
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