Arctic fox behavior shifts reveal key factors for reintroduction success

<p>Understanding how behavioral variation emerges during early development is essential for interpreting individual differences and their ecological relevance. Early-life behavioral development can involve substantial individual variation shaped by biological and social contexts, resulting in differing levels of repeatability across behaviors. In captive-breeding programs, identifying these developmental patterns and their causes can provide a valuable reference for conservation-relevant species. We studied the ontogeny, individual variation, and repeatability of behavior in 138 captive-born Arctic foxes (Vulpes lagopus) in a reintroduction program using repeated focal observations during early and late juvenile periods. Using multivariate Poisson mixed models, we quantified individual- and litter-level variance, assessed temporal and socio-biological influences (i.e., month, sex, sex ratio, litter size), and estimated among- and within-individual behavioral correlations. Juveniles exhibited clear developmental shifts, including reduced play and resting and increased agonistic interactions. Among socio-biological factors, only litter size had a significant effect, with juveniles from larger litters showing elevated vigilance. Crucially, overall repeatability, which incorporates both individual and litter identity, was consistently higher than individual-only repeatability. This divergence indicates that shared early-life environments account for a substantial portion of consistent behavioral variation, whereas individual-level consistency remains comparatively low during the juvenile period. Among-individual correlations were weak, whereas within-individual correlations were stronger for specific behavior combinations. These findings show how early-life behavioral traits are jointly shaped by individual and social factors, clarifying the sources of behavioral variation during development.</p>