Mori, A., Iwamoto, T., & Bekele, A. (1997). A case of infanticide in a recently found gelada population in Arsi, Ethiopia. Primates, 38(1), 79–88.
Abstract: Abstract There have been no reports of infanticide in wild gelada baboons and it has been argued that infanticide is not necessary in geladas, since the birth interval of female gelada can be shortened after takeover of a unit by a new leader male without infanticide. However, we observed an instance of infanticide in a newly-found wild gelada population in the Arsi Region of Ethiopia. After a leader male of the unit was severely wounded by a leopard attack, he was quite weakened. The second male of the unit, a young adult male, became the leader of the unit three weeks later, but the former leader continued to stay in the unit as a second male. After a week, two other adult males joined the unit which, therefore, came to include four adult males. The infanticide took place nine days later. The perpetrator was one of the immigrant males and he showed great interest in the mother of the unweaned victim infant. Although the perpetrator copulated with her after the infanticide, the usurper was found to own all three adult females after two weeks following the infanticide; i.e. the perpetrator could not own any female. The wounded former leader showed conspicuous protective behavior towards the victim's mother and the dead infant. One possible explanation for the occurrence of infanticide in this population of geladas is as follows. Gelada males in this area may be able to join units more easily to form multi-male units but then have shorter tenure in the units. Facing the unstable condition of units, they may sometimes engage in infanticide to increase their breeding opportunities, even before becoming a leader.
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Rudran, R. (1973). Adult male replacement in one-male troops of purple-faced langurs (Presbytis senex senex) and its effect on population structure. Folia Primatol (Basel), 19(2), 166–192.
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Kawamura, S. (1967). Aggression as studied in troops of Japanese monkeys. UCLA Forum Med Sci, 7, 195–223.
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Hinde, R. A. (1969). Analyzing the roles of the partners in a behavioral interaction--mother-infant relations in rhesus macaques. Ann N Y Acad Sci, 159(3), 651–667.
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Saayman, G. S. (1971). Behaviour of the adult males in a troop of free-ranging Chacma baboons (Papio ursinus). Folia Primatol (Basel), 15(1), 36–57.
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Amé, J. - M., Halloy, J., Rivault, C., Detrain, C., & Deneubourg, J. L. (2006). Collegial decision making based on social amplification leads to optimal group formation. Proc. Natl. Acad. Sci. U.S.A., 103(15), 5835–5840.
Abstract: Group-living animals are often faced with choosing between one or more alternative resource sites. A central question in such collective decision making includes determining which individuals induce the decision and when. This experimental and theoretical study of shelter selection by cockroach groups demonstrates that choices can emerge through nonlinear interaction dynamics between equal individuals without perfect knowledge or leadership. We identify a simple mechanism whereby a decision is taken on the move with limited information and signaling and without comparison of available opportunities. This mechanism leads to optimal mean benefit for group individuals. Our model points to a generic self-organized collective decision-making process independent of animal species.
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Menzel, E. W. J. (1971). Communication about the environment in a group of young chimpanzees. Folia Primatol (Basel), 15(3), 220–232.
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Dumont, B., Boissy, A., Achard, C., Sibbald, A. M., & Erhard, H. W. (2005). Consistency of animal order in spontaneous group movements allows the measurement of leadership in a group of grazing heifers. Appl. Anim. Behav. Sci., 95(1-2), 55–66.
Abstract: The term `leadership' has been used in several different senses, resulting in very different ways of identifying leaders and apparently inconsistent conclusions on how leadership is determined in herbivores. We therefore propose the following definitions: (i) a leader is the individual that is consistently the one who initiates long-distance, spontaneous group movements toward a new feeding site and (ii) long-distance spontaneous group movements are movements which happen when an animal changes activity and location and is immediately followed by a similar change in activity and location by other members of the group. Using these definitions, we tested for consistency of movement order across time and situation within a group of fifteen 2-year-old heifers. We found that the same individual was recorded as the very first animal in 48% of movements toward a new feeding site and could therefore be identified as the `leader'. We also showed that movement order when the animals entered an experimental plot, or progressed slowly through the field during a grazing bout, did not produce the same result. This method, which enables us to identify leaders in groups of animals at pasture, should improve our knowledge of how leadership is determined in grazing herbivores.
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Petit, O., & Bon, R. (2010). Decision-making processes: The case of collective movements. Behav. Process., 84(3), 635–647.
Abstract: Besides focusing on the adaptive significance of collective movements, it is crucial to study the mechanisms and dynamics of decision-making processes at the individual level underlying the higher-scale collective movements. It is now commonly admitted that collective decisions emerge from interactions between individuals, but how individual decisions are taken, i.e. how far they are modulated by the behaviour of other group members, is an under-investigated question. Classically, collective movements are viewed as the outcome of one individual's initiation (the leader) for departure, by which all or some of the other group members abide. Individuals assuming leadership have often been considered to hold a specific social status. This hierarchical or centralized control model has been challenged by recent theoretical and experimental findings, suggesting that leadership can be more distributed. Moreover, self-organized processes can account for collective movements in many different species, even in those that are characterized by high cognitive complexity. In this review, we point out that decision-making for moving collectively can be reached by a combination of different rules, i.e. individualized (based on inter-individual differences in physiology, energetic state, social status, etc.) and self-organized (based on simple response) ones for any species, context and group size.
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Overdorff, D. J., Erhart, E. M., & Mutschler, T. (2005). Does female dominance facilitate feeding priority in black-and-white ruffed lemurs (Varecia variegata) in southeastern Madagascar? Am. J. Primatol., 66(1), 7–22.
Abstract: Although many Malagasy lemurs are thought to be female dominant and to have female feeding priority, to date the relationship between these behaviors has been rigorously established only in Lemur catta, and other ways that females might achieve feeding priority have not been examined closely. Erhart and Overdorff [International Journal of Primatology 20:927-940, 1999] suggested that one way female primates achieve feeding priority is to initiate and lead groups to food, thereby gaining access to the food first and positively influencing their food intake compared to other group members. Here we describe female dominance patterns and potential measures of feeding priority in two groups of black-and-white ruffed lemurs (Varecia variegata) that were observed over a 15-month period in southeastern Madagascar. We predicted that the females would 1) be consistently dominant to males, 2) lead groups to food sources more often than males, and 3) have higher feeding rates compared to males when they arrived at food sources first. The results were dissimilar between the study groups. During the study, the oldest adult female in group 1 died. There was no evidence for female dominance in this group, and the remaining (likely natal) female did not lead the group more often, nor did she have a higher food intake than males. Group 1 dispersed shortly after the time frame reported here. In contrast, the resident female in group 2 was dominant to group males (based on agonistic interactions), led the group to food sources more often, and experienced a higher food intake when she arrived first at a food source. How these patterns vary over time and are influenced by the number of females in groups, group stability, food quality, and reproductive condition will be examined in future analyses.
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