Abstract
Understanding the factors associated with the long-term stress levels of captive animals is important from the view of animal welfare. In this study, we investigated the effects of relocation in addition to individual and environmental factors related to social management on long-term stress level in group-living captive chimpanzees by examining behaviors and hair cortisol (HC). Specifically, we conducted two studies. The first compared changes in HC levels before and after the relocation of 8 chimpanzees (Study 1) and the second examined the relationship between individual and environmental factors and individual HC levels in 58 chimpanzees living in Kumamoto Sanctuary (KS), Kyoto University (Study 2). We hypothesized that relocation, social situation, sex, and early rearing conditions, would affect the HC levels of captive chimpanzees. We cut arm hair from chimpanzees and extracted and assayed cortisol with an enzyme immunoassay. Aggressive behaviors were recorded ad libitum by keepers using a daily behavior monitoring sheet developed for this study. The results of Study 1 indicate that HC levels increased during the first year after relocation to the new environment and then decreased during the second year. We observed individual differences in reactions to relocation and hypothesized that social factors may mediate these changes. In Study 2, we found that the standardized rate of receiving aggression, rearing history, sex, and group formation had a significant influence on mean HC levels. Relocation status was not a significant factor, but mean HC level was positively correlated with the rate of receiving aggression. Mean HC levels were higher in males than in females, and the association between aggressive interactions and HC levels differed by sex. These results suggest that, although relocation can affect long-term stress level, individuals’ experiences of aggression and sex may be more important contributors to long-term stress than relocation alone.
Highlights
Social housing is essential to the welfare of some captive animals e.g. [1,2,3]
Hair cortisol (HC) level increased in the first year (2013) after relocation and decreased again in the second year (2014) after relocation compared with that in the former institution (2012) (Fig 1A; Year 2012: mean = 14.5 pg/mg hair; Year 2013: mean = 22.2 pg / mg hair, est. = 0.496, SE = 0.104, t = 4.77, p < 0.001; Year 2014: mean = 11.7 pg / mg hair, est. = -0.227, SE = 0.0716, t = -3.17, p = 0.00153)
The control group showed changes in the HC levels (Fig 1A; Year 2012: mean = 21.7 pg / mg hair; Year 2013: mean = 23.1 pg / mg hair, est. = 0.103, SE = 0.0427, t = 2.39, p = 0.0164; Year 2014: mean = 18.5 pg / mg hair, est. = -0.144, SE = 0.0373, t = -3.86, p < 0.001). Both the relocation and control groups showed changes in HC levels, the HC levels of the two groups differed significantly for 2013 (AIC with relocation-status group 18.4; Akaike Information Criteria (AIC) without relocation-status group 25.0; est. = -0.406, SE = 0.150, t = -2.70, p = 0.0112), whereas it was not different in 2014 (AIC with relocation-status group 14.1; AIC without relocation-status group 15.1; est. = -0.109, SE = 0.068, t = -1.60, p = 0.113) Together with the aforementioned interaction effects, this result indicates that the range of fluctuation was wider in relocation-group chimpanzees
Summary
Social housing is essential to the welfare of some captive animals e.g. [1,2,3]. Wild chimpanzees form multi-male and multi-female groups [4,5,6], and evidence suggests that chimpanzees who are separated from their conspecifics show diverse abnormal behaviors, including self-injurious and stereotypic behaviors, and fail to show certain appropriate, normal social and reproductive behaviors e.g. [7,8,9,10,11]. Providing social stimulation in the form of interaction with conspecifics is one of the most important parts of the care of captive chimpanzees. The formation of complex social groups comparable to that of wild groups is recommended, it can sometimes result in negative consequences. Surplus males emerge, and unnatural social compositions, such as all-male groups, are sometimes formed to solve the problem of surplus animals [15]. [16,17] and integrated into new social groups These factors may lead to long-term stress in captive chimpanzees. In human and non-human animals, social interaction can have both positive and negative consequences, depending on the circumstances and the quality of the relationship e.g. As social relationships are unpredictable and can affect animal welfare for over long period of time, social management plays a role in maximizing the positive effects of these social relationships while reducing the stress derived from them
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