AURORA DONATELLI

PhD Graduate

PhD program:: XXXVII



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.

Research products

11573/1666206 - 2022 - Circadian activity of small brown bear populations living in human-dominated landscapes
Donatelli, Aurora; Mastrantonio, Gianluca; Ciucci, Paolo - 01a Articolo in rivista
paper: SCIENTIFIC REPORTS (London: Springer Nature London: Nature Publishing Group) pp. 1-11 - issn: 2045-2322 - wos: WOS:000859183800054 (8) - scopus: 2-s2.0-85138439425 (8)

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