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Updated: Jul 3, 2026

The Resident-intruder Paradigm: A Standardized Test for Aggression, Violence and Social Stress
Published on: July 4, 2013
Peaceful post-conflict interactions between aggressors and bystanders in captive lowland gorillas (Gorilla gorilla
Elisabetta Palagi1, Elena Chiarugi, Giada Cordoni
1Centro Interdipartimentale Museo di Storia Naturale e del Territorio, Università di Pisa, Calci, Pisa, Italy. betta.palagi@museo.unipi.it
Abstract:
We observed a colony of lowland gorillas in order to assess the occurrence of Peaceful Post-Conflict Interactions between Aggressors and Bystanders (PPIAB). We compared the dynamics of PPIAB with those of Peaceful Post-Conflict Interactions between Victims and Bystanders (PPIVB), which are directed toward victims. We confirmed the occurrence of PPIAB (mean Triadic Contact Tendency: 41.7%+/-16.2% SEM) at frequencies comparable to PPIVB. Immature gorillas were responsible for most PPIAB. PPIAB occurred when the bystander was unrelated to either the aggressor or the victim, and when it was a relative of the aggressor. However, affinitive contact rates were higher in the former case. Unlike PPIVB, PPIAB significantly reduced the likelihood of further aggressions within the group, suggesting that they work at an immediate level. Our data also suggest that bystanders decide when a peaceful contact may be too risky; in fact, neither PPIAB nor PPIVB occurred after high-intensity aggressions.
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