Comportamento di marcatura degli alberi nell'orso bruno: analisi dei fattori che influenzano la selezione dell'albero e l'intensità del marcaggio

Chemical signals, which are spread by different means, like urine, faeces or glandular secretions, are considered the main channel of communication in many mammalian species. Indeed, olfactory chemical signals, usually left on conspicuous and permanent substrates (e.g. trunks), persist for a longer time compared to visual and vocal communication. This facilitates the interactions between individuals, without any need to overlap simultaneously at a given site and time. The brown bear (Ursus arctos), like other mammals, mainly performs chemical communication through scents deposited on marking (rub) trees. In this study, the characteristics of 101 brown bear rub trees were compared with 263 control trees in the Cantabrian Mountains (NW Spain), and were analyzed the potential factors affecting the density of rub trees along 35 surveyed footpaths. In addition, were explored the features of each marked tree surroundings and their role in marking probability. Specifically, three main hypotheses have been formulated: (1) Bears would select specific trees, or tree species with characteristics that make them more conspicuous; (2) Rub trees would be more abundant towards the core of the bear distribution area, in areas with higher bear density. (3) Significant differences exist between the landscape features of the areas in which rub trees were found and the areas in which they were absent. The results showed that the characteristics of trees have a role in affecting brown bears selection of more conspicuous trees with a preference for birches (Betula spp.). This choice may facilitate the marking and/or detection of chemical signals and the effectiveness of intraspecific communication. On the other hand, the abundance of rub trees along footpaths did not seem to depend on the density of bear observations or their relative position within the population centre or its border. Furthermore, the landscape around rub trees was mainly covered by deciduous forest, it did not include human settlements and it was quite close to rivers and paths. These findings can also be used to locate target trees that could help in population monitoring. In fact, understanding the rubbing behaviour could be useful for a better management and conservation of the population considered “endangered” in the Cantabrian region.