Does moonlight affect movement patterns of not obligate carnivores? Brown bears do not mind that moon exists

Abstract

Moonlight has a prominent role in shaping prey-predator relationships, i.e. as light intensity increases, prey species reduce their activity and become more vigilant, which consequently influence the activity rhythms of predators. Selection pressures may exist on carnivores to be more active on bright moonlit nights, as they should search more intensively for prey. In the same way, carnivores may also benefit from high light levels when hunting, being more lethal during the brightest hours of the night. The analysis of movement patterns of carnivores can improve our current knowledge on how moonlight may alter the behaviour of a group of species with so diverse ecological needs. In this context, the brown bear Ursus arctos is an intriguing large carnivore for three reasons: (1) even if brown bears have the typical morphological features of carnivores they are facultative carnivores, i.e. they do not strictly depend on prey rhythms of activities; (2) they are not strictly nocturnal and, thus, brown bears might be less related to the moon phases than many other strictly nocturnal carnivores; and to our knowledge, (3) all the studies on the effect of the moonlight on carnivores have been carried out on obligate carnivores. To determine whether the lunar phases may have an influence on brown bear movements, we studied daily movement behaviours of 71 brown bears (42 males and 29 females) in Finland and Russian Karelia between 2002 and 2014. We hypothesise that (1) movement patterns will not show any dependence of bears on moonlight, i.e. bears would not modulate their predation activities according to light intensity and therefore we will not see an increase in movements around the full moon phase, and (2) moonlight might influence the decision to move into the den to start hibernation. Indeed, it might be safer to enter dens in low light conditions, i.e. close to the new moon phase. As expected, brown bear movements did not vary according to moonlight but, contrary to our prediction, moonlight showed no influence on the date of den entry. We suggest that, even if brown bears have the morphological features of carnivores, they are opportunistic omnivores with a diversified diet and, as a result, the prey-predator relationships that are behind the dependence of carnivores to lunar light are weaker than in obligate carnivores. Additionally, two factors may have played a role to reduce a potential effect of the moon: (1) feeding patterns might be disrupted by the presence of artificial feeding points established for hunting and bear viewing purposes; and (2) this bear population is managed through hunting, and bears under hunting pressure show alteration of their normal activity rhythms and movements to avoid hunters.