Effects of changing housing conditions on mangabey behavior (Cercocebus atys): Spatial density, housing quality, and novelty effects

Abstract

The separate influences of spatial density and housing quality on the behavior of captive animals are difficult to measure because the two factors are often intrinsically linked. Here, we recorded affiliative and agonistic behavior in adult sooty mangabeys in various housing situations, testing spatial density and housing quality changes separately (N=26 experienced spatial density changes; N=12 experienced housing quality changes). We varied spatial density by 50% while holding housing quality constant and we varied housing quality while holding spatial density constant (achieved by comparing two types of run-housing that varied in the amount of visual privacy and outdoor access). Each housing condition was one month in duration. Prior to collecting data in each housing condition, we evaluated the subjects’ initial responses to the change in housing environment during two-week novelty periods. Affiliative behavior did not change during the novelty periods. Agonistic behavior initially increased slightly when spatial density increased and it decreased significantly when spatial density decreased; it also decreased when subjects moved to housing that offered more visual privacy and outdoor space, indicating that the mangabeys were sensitive to these housing changes. After the novelty periods, affiliative behavior increased under higher spatial density, but remained unchanged across housing quality conditions; agonistic behavior remained unchanged across all conditions. Results suggest that a prolonged increase in spatial density led the mangabeys to adopt a tension-reduction coping strategy, in which the increase in affiliative behavior alleviates a presumed increase in social tension. Reducing visual privacy and choice did not affect the mangabeys’ behavior, post-novelty period. Thus, like many other primates, the mangabeys managed tension by flexibly adapting to changes in their housing environment in ways that reduce the risk of severe aggression. This study highlights the importance of controlled behavioral studies in facilitating data-driven management decisions that promote animal welfare.

Hypotheses for the Evolution of Reduced Reactive Aggression in the Context of Human Self-Domestication

“…On the other hand, genetic data indicate that effective population size of H. sapiens fell from 200,000 years ago to 50,000–30,000 years ago, suggesting a mismatch between cultural development and population density (Steele and Weaver, 2014). Furthermore among wild monkeys and apes there is no evidence for an association between population density and social tolerance (Wrangham, 2014); and experimental studies of captive primates show that high population density can lead to an increase in the rate of aggression, or can have no effect (Cordoni and Palagi, 2007; Crast et al, 2015). The population density hypothesis also fails to detail any process responsible for selection directly against alpha-male-style behavior.…”

“…Current evidence about the evolutionary history of human population density, however, undermines any easy correlations, and the relationship between population density and rates of aggression in primates is inconsistent. Studies of causal mechanisms may prove helpful by specifying the conditions in which increased population density leads to reduced reactive aggression (Crast et al, 2015).…”

Social network changes during space restriction in zoo chimpanzees

“…Much research has demonstrated how nonhuman primates flexibly use various coping strategies to avoid conflict and reduce social tension in response to reduced space availability (Anderson et al 1977; Aureli et al 1995; Aureli and de Waal 1997; Caperos et al 2011; Caws and Aureli 2003; Cordoni and Palagi 2007; Crast et al 2015; de Waal 1989; Duncan et al 2013; Judge and de Waal 1993, 1997; Judge et al 2006; Nieuwenhuijsen and de Waal 1982; Sannen et al 2004; Tacconi and Palagi 2009; Videan and Fritz 2007; van Wolkenten et al 2006). In contrast to an earlier influential study on rats that linked increased spatial density to increased aggression (The Density-Aggression Model, Calhoun 1962, validated in a range of species, e.g., dwarf mongoose Helogale undulata rufula , Rasa 1979; rabbits, Oryctolagus cuniculus , Myers 1966; baboons, Papio anubis , Elton and Anderson 1977; pigtailed macaques, Macaca nemestrina , Erwin and Erwin 1976), these studies have supported an alternative view: Under space restriction, social mechanisms are activated within groups of primates, such as avoiding potential aggressors and offering appeasement, which reduce the likelihood and/or intensity of aggression (The Coping Model, de Waal 1989).…”

“…One of these strategies is the tension-reduction strategy, where individuals increase affiliative and appeasement behaviors as spatial density increases in order to alleviate tension, increase tolerance, and minimize the likelihood of conflict escalation (Caperos et al 2011; Crast et al 2015; Duncan et al 2013; Nieuwenhuijsen and de Waal 1982; Novak et al 1992; Judge and de Waal 1997; Judge et al 2006; Sannen et al 2004; Videan and Fritz 2007). Another strategy is the conflict-avoidance strategy, where individuals reduce how often they actively seek interactions with others, leading to a decrease in affiliative behavior and a lack of aggressive escalation; whilst severe aggression does not increase, mild threats can increase (Aureli et al 1995; Duncan et al 2013; Judge and de Waal 1993; van Wolkenten et al 2006; Videan and Fritz 2007).…”

Reproductive males are effective at managing conflict in captive Sulawesi crested macaques (Macaca nigra)

“…Short-term increases in social density result in both immediate increases in low to medium intensity aggression, as well as significant decreases in all levels of social behavior (Aureli et al, 1995;Crast et al, 2015;de Waal, 1989;Sannen et al, 2004). Under long-term crowding, however, these effects become less pronounced as the novelty of high-density social conditions abates (Crast et al, 2015).…”