Intergroup lethal gang attacks in wild crested macaques (Macaca nigra).

• Published in: Animal Behaviour
• Main Authors: Martínez-Íñigo, Laura, Engelhardt, Antje, Agil, Mohamed, Pilot, Malgorzata, Majolo, Bonaventura
• Format: Article in Journal/Newspaper
• Language: English
• Published: Association for the Study of Animal Behaviour / Elsevier 2021
• Subjects: C800 Psychology; Canis lupus
• Online Access: https://eprints.lincoln.ac.uk/id/eprint/46578/; https://eprints.lincoln.ac.uk/id/eprint/46578/1/ANBEH-D-20-00915.docx; https://doi.org/10.1016/j.anbehav.2021.08.002

Lethal gang attacks, in which multiple aggressors attack a single victim, are among the most widespread forms of violence between human groups. Gang attacks are also frequent in some other social mammals, such as chimpanzees (Pan troglodytes), wolves (Canis lupus), spotted hyaenas (Crocuta crocuta), and meerkats (Suricata suricatta). So far, species where gang attacks have been observed share one or more of these socio-ecological features: territoriality, fission-fusion, cooperative breeding or coalitionary bonds. However, the scarcity of data in other taxa makes it challenging to determine if one/all of these socio-ecological features are necessary and sufficient to drive the evolution of gang attacks. Here we describe the first-ever reports of intergroup gang attacks in the crested macaque, using data on three groups collected over 13 years, with the joint observation times for the three groups summing up to 37 years. Crested macaques gang attacked outgroup conspecifics when aggressors were numerically superior to victims. Adult females were the most frequent age/sex category to attack outgroup conspecifics. The victims were mostly adult females, and infants. We propose that coalitionary bonds, hostility towards outgroup individuals, and the ability to estimate numerical odds may suffice to trigger intergroup gang attacks when the conditions favour an imbalance of power between victims and attackers.