Early and late cognitive and behavioral aspects associated with range use in free-range laying hens (Gallus gallus domesticus)

Individual differences in free-range chicken systems are important factors influencing how birds use the range (or not), even if individuals are in the same environmental conditions. Here, we investigated how various aspects of the birds' behavioral and cognitive tendencies, including their optimism/pessimism, cognitive flexibility, sociability, and exploration levels, are associated with range use and how they may change over time (before and after range access). To achieve this, one hundred White Leghorn laying hen chicks underwent three distinct behavioral/cognitive tests—the cognitive bias test, the detour test, and the multivariate test—prior to gaining access to the range, between 9 and 39 days of age. After range access was allowed (from day 71), bird's range use was evaluated over seven non-consecutive days (from 74 to 91 days of age). Subsequently, a subset of birds, classified as high rangers (n = 15) and low rangers (n = 15) based on their range use, underwent retesting on the same three previous tests between 94 and 108 days of age. Our results unveiled a negative correlation trend between birds' evaluation of the ambiguous cue and their subsequent range use (rho = -0.19, p = 0.07). Furthermore, low rangers were faster to learn the detour task (χ2 = 7.34, df = 1, p = 0.006), coupled with increased sociability during the multivariate test (rho = -0.23, p = 0.02), contrasting with their high-ranging counterparts, who displayed more exploratory behaviors (F(1,27) = 3.64, p = 0.06). These behavioral patterns fluctuated over time (before and after range access); however, conclusively attributing these changes to birds' aging and development or the access to the range remains challenging. Overall, our results corroborate that behavioral and cognitive individual differences may be linked to range use and offer novel perspectives on the early behavioral and cognitive traits that may be linked to range use. These findings may serve as a foundation for adapting environments to meet individual needs and improve animal welfare in the future.