Urbanization and deforestation impose severe challenges to wildlife, particularly for forest-living vertebrates. Understanding how the peri-urban matrix impacts their survival is critical for designing strategies to promote their conservation. We investigated the threats faced by brown howler monkeys (Alouatta guariba clamitans) in peri-urban regions of Rio Grande do Sul (RS) and Santa Catarina (SC) states, southern Brazil, by compiling conflicts reported over more than two decades. We assessed

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... the major conflicts, their distribution among age-sex classes, and the predictors of conflict-related mortality using GLMMs. After 20+ years of monitoring, we compiled 540 conflicts (RS=248 and SC=292). Electrocution in power lines was the most frequent cause of death or injury (37%), followed by dog attack (34%), run over (17%), and human mistreatment (12%). The occurrence of lethal injuries ranged from 5% to 69% depending on the type of conflict and state. The overall post-conflict mortality was 56%. Adult males and females were the major victims in both states. The minimal adequate GLMM explained 83% of the variation in conflict-related mortality. State, conflict type, and age-sex class were the main predictors of mortality. Overall, mortality was lower in SC and after human mistreatment, and higher among adult females than in the other classes. We found that the survival of brown howlers in the forest-urban interface is constrained by both the urban infrastructure and the growing interactions with humans and domestic and stray dogs. We propose the placement of aerial bridges, road signs and speed bumps in areas of frequent animal crossing, the sterilization of stray dogs, and the sensitization of local inhabitants on the importance of respecting and protecting wildlife to reduce their conflicts with humans and domestic animals in the forest-urban interface.