Age Ain’t Nothing But a Number: factors other than age shape brown bear movement patterns

Movement patterns may reflect individual age-specific variation. For example, individuals that sample novel areas (e.g. natal dispersal) may show different movements from those of adults settling in more stable areas and moving around local environments to procure food and shelter. The long-term study of a solitary large carnivore, the brown bear, Ursus arctos, allowed us to test for age-related differences in movement behaviour and, more specifically, for potential inter- versus intraindividual variation among adult versus subadult bears. In addition to age, we also explored factors other than individual characteristics that have the potential to determine movement patterns: sex, season (mating versus hyperphagia) and body weight. The contribution of age to movement patterns seemed to be irrelevant, most of the observed movement patterns being primarily explained by season and body weight. Moreover, intraindividual movements within a home range were more marked among subadult brown bears. We hypothesize that two mechanisms may lead to subadults and adults moving similarly. First, both must hibernate and, consequently, need to store energy during hyperphagia. Second, although triggered by different factors, both make erratic/long movements after hibernation, for dispersal (subadults) or mating (adults), which might contribute to shaping similar movement patterns. Different motivations could thus be expressed through the same behavioural patterns, and equifinality (i.e. similar ecological patterns emerge from different initial conditions) might be considered an intrinsic property of animal behaviours.