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. With a rare and comprehensive dataset based on repeated individual-based observations of more than 130 captive-born Arctic foxes across multiple years, we provide an in-depth analysis of behavioral development during the juvenile stage in this wild canid, a locally endangered and globally recognized carnivore. Through a robust analytical framework that integrates ontogenetic, socio-biological, and individual-level influences, this study provides novel insights into early-life behavioral dynamics, highlighting patterns of association and the degree of behavioral repeatability in a socially flexible species. These findings have broader implications for behavioral ecology and deepen our understanding of the causes of early-life behavioral variation, while also offering valuable guidance for behavior-informed conservation strategies.
Choi et al. (Sun,) studied this question.