Gartland, K. N., Carrigan, J., White, F. J. 2021. Preliminary relationship between overnight separation and wounding in bachelor groups of western lowland gorillas (Gorilla gorilla gorilla). Applied Animal Behaviour Science 241, 105388.

Despite no significant difference in wounding between bachelor and mixed-sex groups of western lowland gorillas (Gorilla gorilla gorilla) in zoological settings, anecdotal concerns around the frequency and severity of wounding in bachelor groups have perpetuated opinions of all-male units as inherently less stable. Bachelor groups are prevalent within zoological organizations and necessitate specialized care and protocols separate from those for mixed-sex groups. We collected survey data on 59 gorillas in 21 bachelor groups across 19 zoos. This survey broadly encompassed group social and demographic history, exhibit design, management practices, and wounding over the past year. Previous experience suggested that overnight housing conditions could be an important influencing factor on wounding rates. We ran Pearson’s Correlations and ANOVAs to examine wounding within the context of overnight housing conditions as well as other management and demographic factors. We found a significant negative correlation between group duration and wounding rate such that wounding rate was lower in groups that were together longer if and only if groups were separated overnight (r=-0.62, N = 11, p = 0.04). This was further supported by ANOVAs which demonstrated that groups that have been together for longer had significantly higher rates of wounding when housed together overnight than when housed separately overnight (F = 3.51, df = 3, 17, p = 0.04). Finally, we found that mature silverbacks housed socially overnight sustain significantly more wounds than mature silverbacks housed separately overnight (F = 4.11; df = 1,31; p = 0.05). Based on our analyses, overnight housing conditions have a significant impact on wounding particularly when paired with long-term (> 7 years) group social history. We recommend that groups with long social histories or primarily mature members be separated overnight should housing facilities allow.

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