Does group size matter? Captive chimpanzee (Pan troglodytes) behavior as a function of group size and composition

Abstract

The National Institutes of Health and the Association of Zoos and Aquariums recommend that captive chimpanzees be housed in multi-male, multi-female, age-diverse groups of no less than seven individuals. These recommendations are rooted in the idea that captive chimpanzee groups should be modeled after free-ranging, wild, fission-fusion chimpanzee societies. However, captive chimpanzees do not face the environmental pressures faced by wild chimpanzees, including food scarcity, inter-group competition, and predation. As such, it has been posited that wild, natural conditions may not be the most relevant metric for defining optimal captive chimpanzee group sizes and compositions. Additionally, captive housing poses a set of restrictions on group sizes and compositions, including the need to balance large, multi-male groups with space per animal limitations and intra-group aggression. In the present study, we examined the behavioral effects of group size, within-group age range, and percentage of males in the group. We collected 713 hr of focal animal samples across 120 captive chimpanzees housed in social groups of 4–10 individuals using a 58-behavior ethogram. Chimpanzees housed in groups with a large age range exhibited less inactivity and more locomotion than chimpanzees housed in groups with smaller age ranges. Additionally, chimpanzees in groups of ≥7 with less than half males showed the highest levels of locomotion. Lastly, chimpanzees in groups of ≥7 with at least half males showed the highest levels of affiliation. There were no other significant differences in behavior as a function of these variables or their interactions. These findings lend some support to the existing group size and composition recommendations, providing empirical evidence that there may be certain advantages to housing captive chimpanzees in larger groups with a more diverse age range and/or more males. These results also have practical implications for behavioral management programs across captive settings.

Effects of personality and rearing-history on the welfare of captive Asiatic lions (Panthera leo persica)

“…In this study we measured the evenness of enclosure use, which represents the functional space of the enclosure rather than available space. We found that small variations in enclosure sizes do not associate with significant shifts in behavioural welfare of Asiatic lions, which is in line with previous studies that place more importance on enclosure design (Tan et al, 2013), complexity and species-appropriateness than enclosure area (Rose & Robert, 2013;Herrelko, Buchanan-Smith & Vick, 2015;Neal Webb, Hau & Schapiro, 2018). The correlation between enclosure size and space usage bias was weak but positive, which means that increasing enclosure sizes were associated with higher zone-usage bias.…”

Differences in Behavior Between Elderly and Nonelderly Captive Chimpanzees and the Effects of the Social Environment

“…Data were analyzed by using the techniques that we have published previously. [29][30][31] Briefly, durations of each behavior were averaged across all observations for each chimpanzee, with 'in-view' duration as the denominator. Average duration was then converted into a percentage of total time (that is, percentage of time of behavior = [duration of behavior / in-view duration] × 100%).…”

“…Mobility impairment scores, group size, within-group age range, and percentage of male chimpanzees in the group were used as covariates. 31 The remaining analyses focused only on elderly chimpanzees and the effects of social housing conditions on behavior and wounding. Because group size and the average age of the group were significantly negatively correlated (r = -0.78, P = 0.0001), we were unable to assess the effects of these factors independently.…”

“…As part of a larger project examining the behavioral and welfare effects of refinements to behavioral management techniques and the captive environment at the NCCC, we aimed to examine captive chimpanzee behavior as a function of advanced age and the social environment. [29][30][31] We were specifically interested in the following questions. First, using the definition of elderly as 35 y and older proposed by past literature, in what ways does overall behavior differ between elderly and nonelderly chimpanzees?…”

Peer Review #3 of "Effects of personality and rearing-history on the welfare of captive Asiatic lions (Panthera leo persica) (v0.2)"

“…that place more importance on enclosure design(Tan et al, 2013), complexity and species-appropriateness than enclosure area(Rose & Robert, 2013;Herrelko, Buchanan-Smith & Vick, 2015;Neal Webb, Hau & Schapiro, 2018). The correlation between enclosure size and space usage bias was weak but positive, which means that increasing enclosure sizes were associated with higher zone-usage bias.…”