Andean bear tree selectivity for scent-marking in Ecuadorian cloud forests

Olfactory signalling is the most efficient mode of animal communication between a signaller and a receiver when receiver’s presence is unpredictable. Scent-marking requires selective strategies to increase the likelihood that these signals persist in the environment and are successfully received. Bears are solitary, non-territorial carnivores, which scent-mark trees, substrate, and other objects to communicate with conspecifics. Signallers place scent marks on trees to increase the detectability of their signals, and possibly also to communicate their size and status. We assessed scent-marking tree selectivity of Andean bears, Tremarctos ornatus, in Ecuadorian cloud forests at two spatial scales: the individual-tree level and at a local scale (3-m radius). We recorded characteristics of marked and unmarked trees along bear trails (5.49 km in total) in the Eastern Cordillera of the Ecuadorian Andes, near the Sumaco Biosphere Reserve. To decrease dimensionality and multicollinearity before explanatory analyses, we performed Principal Component Analysis on data from 467 trees (65 marked trees, 54 control trees, 348 radius plot trees) of 48 tree species. We then used Generalized Linear Models, model selection, and model averaging to discover that Andean bears preferred rubbing leaning trees, aromatic tree species, and hardwood trees with smaller and thicker leaves containing less nitrogen. Thirteen of 59 marking sites contained multiple marked trees, but site-level data do not indicate why bears marked multiple trees at some sites but not others. We thus encourage further analyses of marked-tree cluster sites and their relationship to productive food resources and reproduction, which might present important communication hubs for ursids.