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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.anbehav.2009.02.012 Byline: Chihiro Hiramatsu (a), Amanda D. Melin (b), Filippo Aureli (c), Colleen M. Schaffner (d), Misha Vorobyev (e), Shoji Kawamura (a) Abstract: It is not well understood how primates combine olfactory and visual cues in their natural behaviour, especially during feeding. In this study we conducted field observations of a group of wild, frugivorous black-handed spider monkeys, Ateles geoffroyi (Platyrrhini), consisting of both dichromats (N =11) and trichromats (N =9) in Santa Rosa National Park, Costa Rica. We focused on the fruit foraging behaviour, for which involvement of vision has been well studied. We examined how often the monkeys inspected fruits by sniffing them during their fruit feeding attempts (i.e. sniffing index). We found that both dichromats and trichromats sniffed the visually cryptic fruit species more often than the conspicuous species, with the sniffing index being negatively correlated with the luminance and blue-yellow contrasts of fruits to background leaves. Furthermore, the sniffing index was negatively correlated with the proportion of fruits eaten (versus rejected) following a foraging attempt in both dichromats and trichromats. These results suggest that monkeys use olfaction for discrimination between edible and inedible fruits when vision alone is insufficient to evaluate the quality of fruits, showing the first documentation of interplay between vision and olfaction in primate feeding behaviour under natural conditions. Author Affiliation: (a) Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Japan (b) Department of Anthropology, University of Calgary, Canada (c) Research Centre in Evolutionary Anthropology and Palaeoecology, School of Natural Sciences and Psychology, Liverpool John Moores University, U.K. (d) Psychology Department, University of Chester, U.K. (e) Department of Optometry and Vision Science, University of Auckland, New Zealand Article History: Received 16 January 2009; Revised 2 February 2009; Accepted 20 February 2009 Article Note: (miscellaneous) MS. number: 09-00039

Raids into neighboring territories may occur for different reasons, including the increase of foraging and mating opportunities directly or indirectly through the killing of neighboring rivals. Lethal raids have been mainly observed in humans and chimpanzees, with raiding males being reported to search purposefully for neighbors. Here we report on the first cases ever witnessed of raiding parties of male spider monkeys, a species expected to show such a behavioral tendency, given its similarity with humans and chimpanzees in critical socio-ecological characteristics, such as fission-fusion social dynamics and male-male bonding. Despite the high degree of arboreality of spider monkeys, all seven witnessed raids involved the males progressing single file on the ground in unusual silence. This is remarkably similar to the behavior of chimpanzees. The circum stances around the raids suggest that factors such as reduced mating opportunities, number of males relative to that in the neighboring community, and the strength of bonds among males could play a role in the timing of such actions. The raids did not appear to be aimed at finding food, whereas there is some indication that they may directly or indirectly increase reproductive opportunities. Although no killing was observed, we cannot exclude the possibility that spider monkey raids may be aimed at harming rivals if a vulnerable individual were encountered. The similarity of spider monkey raids with those of chimpanzees and humans supports the notion that lethal raiding is a convergent response to similar socio-ecological conditions. KEY WORDS Ateles; coalitionary killing; fission-fusion; male bonding

Evidence and causes of intragroup coalitionary aggression leading to the death of a wild young adult male spider monkey is reported. A young adult male from a well-habituated community at the Otoch Ma'ax Yetel Kooh reserve in Yucatan, Mexico, sustained repeated severe injuries between January and March 2002, and on April 1, 2002, the same male was the victim of an intragroup attack by at least one adult male, which resulted in his death.

The relationship between group size and aggression towards strangers in Wied's black tufted-ear marmosets (Callithrix kuhli) is investigated. The behavior of breeding males from small groups was not found to differ from the behavior of those from large groups. However, breeding females from large groups exhibited more aggressive behavior towards strangers, engaged in more scent-marking and spent more time near their partners after exposure to female intruders. The findings indicate that breeders from small groups are more tolerant of strangers than those from large groups, thereby facilitating the recruitment of new group members.