Recommendations for Abnormal Behaviour Ethograms in Monkey Research

Simple Summary Monkeys are at risk of performing abnormal behaviours in captivity: signs of poor well-being that are easily recognizable. For practical reasons, researchers typically pool different abnormal behaviours together. However, this is typically performed without assessing whether the behaviours are actually related to each other. Consequently, such subcategories may be misclassifying behaviours. Most importantly, using arbitrary subcategories may reduce their precision to measure animal welfare since different abnormal behaviours are likely to have distinct risk factors and treatments. We therefore investigated the validity of four previously used abnormal behaviour subcategories in laboratory rhesus monkeys (i.e., we assessed whether the subcategories were actually formed of behaviours that co-occurred). These included behaviours previously labelled 'self-injurious' (e.g., self-biting), 'self-stimulating' (e.g., hair-pulling), 'postural' (e.g., floating limb), and 'motor' (e.g., pacing). Using a large dataset on 19 different types of abnormal behaviour from over a thousand monkeys, we discovered that none of the subcategories analyzed were valid. Therefore, we reanalyzed the data to create four new valid subcategories that were formed of related behaviours. We additionally identified four behaviours that were not related to any other behaviour and should thus be categorized alone. Once replicated, using this new validated scheme will help researchers and laboratory staff study the conditions that trigger them and develop the most appropriate treatment strategies. Laboratory monkey ethograms currently include subcategories of abnormal behaviours that are based on superficial morphological similarity. Yet, such ethograms may be misclassifying behaviour, with potential welfare implications as different abnormal behaviours are likely to have distinct risk factors and treatments. We therefore investigated the convergent validity of four hypothesized subcategories of abnormal behaviours ('motor', e.g., pacing; 'self-stimulation', e.g., self-sucking; 'postural', e.g., hanging; and 'self-abuse', e.g., self-biting). This hypothesis predicts positive relationships between the behaviours within each subcategory. Rhesus macaque (Macaca mulatta) data on 19 abnormal behaviours were obtained from indoor-housed animals (n = 1183). Logistic regression models, controlling for sex, age, and the number of observations, revealed that only 1/6 'motor' behaviours positively predicted pacing, while 2/3 'self-abuse' behaviours positively predicted self-biting (one-tailed p-value < 0.05). Furthermore, 'self-stimulation' behaviours did not predict self-sucking, and none of the 'postural' behaviours predicted hanging. Thus, none of the subcategories fully met convergent validity. Subsequently, we created four new valid subcategories formed of comorbid behaviours. The first consisted of self-biting, self-hitting, self-injurious behaviour, floating limb, leg-lifting, and self-clasping. The second comprised twirling, bouncing, rocking, swinging, and hanging. The third comprised pacing and head-twisting, while the final subcategory consisted of flipping and eye-poking. Self-sucking, hair-plucking, threat-biting, and withdrawn remained as individual behaviours. We encourage laboratories to replicate the validation of these subcategories first, and for scientists working with other species to validate their ethograms before using them in welfare assessments.

Automated summary

Monkeys in captivity often display abnormal behaviors, which are poorly categorized by current subcategories. Therefore, researchers have investigated and identified new valid subcategories to accurately assess animal welfare.