Thesis title: Circadian activity rhythms of brown bears (Ursus arctos) in the Anthropocene
Daily activity rhythms represent the behavioral aspect of the wake-sleep cycle and are the product
of a complex interplay of endogenous and exogenous factors. Wildlife diel organization of activity
contributes to fitness through the optimization of foraging efficiency, avoidance of competition,
and thermoregulation, among other aspects, by tracking daily changes in external conditions. The
intensification of human encroachment in pristine landscapes is impacting wildlife behavior in
several ways. Recent studies have demonstrated an increase in nocturnality in many species
inhabiting human-modified landscapes, possibly as a strategy to temporally segregate from
humans. Among wildlife species, large carnivores may be particularly vulnerable to the effects of
human pressure, given their large spatial requirements, slow life histories, low population
densities, and the possibility of conflict with humans. Both large carnivore activity patterns and
the effects of modifications in activity rhythms in terms of fitness are still largely unknown,
although the former is recently gathering great interest among wildlife biologists.
In this thesis, I review published literature on large carnivore activity patterns and propose a
standardized lexicon, I develop an improved approach to model circadian activity of wildlife, and
I estimate daily activity rhythms of brown bears (Ursus arctos) in a variety of landscapes and
gradients of human pressure. Specifically, I modeled daily activity patterns using a Bayesian
framework including a circular hour of the day effect, with the covariance between hours
dependent on their temporal distance. This method takes into consideration the autocorrelation
structure of activity data, which is rarely accounted for in most commonly used methodologies to
estimate circadian activity. I applied this novel approach to evaluate drivers of activity in brown
bear populations across Europe and North America (i.e., Apennine, Dinaric Pindos, Karelian,
Scandinavia, and Yellowstone populations) by means of GPS telemetry and accelerometers. I
found that demographic parameters (i.e., sex and reproductive status), human disturbance, and
ambient temperature were the most compelling factors in shaping bear daily activity rhythms
among the ones analyzed. In addition, the results from this thesis suggest that intense human
pressure and high bear densities, increasing competition and possible risk of infanticide, limited
the flexibility of bear activity patterns and, possibly, their adaptability to environmental changes.
Although nocturnality can be an adaptive strategy to face the intensification of landscape
anthropization and increasing temperatures due to climate change, results from this thesis prompt
further investigation into the mechanisms linking activity tactics to fitness.