Abstract
Adverse rearing conditions are considered a major factor in the development of abnormal behavior. We investigated the overall levels, the prevalence and the diversity of abnormal behavior of 18 adult former laboratory chimpanzees, who spent about 20 years single caged, over a two-year period following re-socialization. According to the onset of deprivation, the individuals were classified as early deprived (EDs, mean: 1.2 years) or late deprived (LDs, mean: 3.6 years). The results are based on 187.5 hours of scan sampling distributed over three sample periods: subsequent to re-socialization and during the first and second year of group-living. While the overall levels and the diversity of abnormal behavior remained stable over time in this study population, the amplifying effects of age at onset of deprivation became apparent as the overall levels of abnormal behavior of EDs were far above those of LDs in the first and second year of group-living, but not immediately after re-socialization. The most prevalent abnormal behaviors, including eating disorders and self-directed behaviors, however, varied in their occurrence within subjects across the periods. Most important, the significance of social companionship became obvious as the most severe forms of abnormal behavior, such as dissociative and self-injurious behaviors declined.
Highlights
Abnormal behavior, by definition, is “rarely seen in wild populations and does not promote the success and the survival of the individual or its close relatives” [1]
Across all 18 chimpanzees, the percent of scans spent on abnormal behavior did not differ significantly between sampling periods, i.e., abnormal behavior was frequent in 2003, 2004 and 2005 in the social setting
In the MS1 group, by contrast, we found a significant increase in the performance of abnormal behaviors from 2003 to 2004 (Table 2)
Summary
By definition, is “rarely seen in wild populations and does not promote the success and the survival of the individual or its close relatives” [1]. It is well known that adverse early rearing conditions and restricted environments may be conducive to the development of abnormal behavior in diverse animal species, including humans [3,4]. Davenport’s [10] assumption, that in chimpanzees the development of stereotypic behavior may be prevented by maternal care during the first year of an infant’s life, proved wrong, as even mother-reared subjects developed abnormal behaviors in captive environments [11]. Abnormal behaviors were depicted quantitatively in zoo chimpanzees originating from various backgrounds [11,17]. These surveys revealed the impact of restricted rearing conditions on the development of specific abnormal behaviors [11,15]. The sooner the onset of maternal deprivation and the longer the lifetime spent in invasive research, the higher are the levels of behavioral aberrancies [16]
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