Boredom-like states in mink and their behavioural correlates: A replicate study

Scientists and laypeople have long expressed concern that animals in non-enriched, unchanging environments might experience boredom. However, this had attracted little empirical study: the state is difficult to assess without verbal self-reports, and spontaneous behavioural signs of boredom can vary in humans, making it hard to identify signs likely to be valid in other species. We operationally define boredom as a negative state induced by barren conditions that causes an increased, generalised interest in diverse stimuli. Previously, we demonstrated that this state existed in mink housed in non-enriched cages, compared to those in preferred, stress-reducing enriched enclosures. Further, in some analyses this heightened interest in stimuli positively correlated with time spent lying still but awake, while negatively correlating with locomotor stereotypic behaviour. However, these results needed replication. The current study tested for the same effects, in a new cohort of 20 male mink, by presenting 11 stimuli ranging from those predicted to typically be aversive (e.g. predator cues) to those predicted to be rewarding (e.g. food rewards; moving objects to chase). Where housing treatments differed, non-enriched mink were again more interested in the stimuli presented, spending longer oriented towards and in contact with them (e.g. for aversive stimuli: F1,9 = 6.27, p = 0.034 and F1,9 = 8.24, p = 0.019, respectively). Lying still but awake again correlated with interest in the stimuli (shorter latencies to contact rewarding stimuli: F1,17 = 3.70, p = 0.036; in enriched mink only, more time oriented to and in contact with all stimuli: F1,8 = 9.49, p = 0.015 and F1,8 = 15.9, p = 0.004). In contrast, the previous correlations with stereotypic behaviour were not replicated. We therefore conclude that mink housed in non-enriched cages likely experience boredom-like states, and that time spent lying still while awake could, at least in some types of housing, potentially be used as a cage-side indicator of these states. We also suggest how future researchers might address further fundamental and practical questions about animal boredom, in mink and other species.