Selective Scratchers

An Analysis of Grizzly Bear Rub Tree Characteristics in SW Alberta

Abstract

Grizzly Bears (Ursus arctos) have been shown to exhibit rubbing behavior on “rub trees” as a form of intra-specific communication. By leaving chemical cues on trees, the signaling individual can convey information in the absence of physical contact with conspecifics. The criteria that bears use to select rub trees is unclear, especially within characteristic bear habitats in SW Alberta. We surveyed rub tree characteristics in Alberta’s BMA5 (1685km2), near Crowsnest Pass. Analyses of these characteristics showed that the majority of rub trees were located on flat ground, with a slight south-facing orientation (58.7%) and within 3.3m of a trail. Bear hair was found on 99.4% of trees, with 88% featuring discoloured and smooth bark. The most common rub tree species was Lodgepole Pine (56.3%), followed by White Spruce (15.9%) and Engelmann Spruce (8.7%). By comparing rub tree characteristics to those of trees in adjacent stands, we found the presence of “rare” rub tree species. The most common rare rub tree species was Lodgepole Pine (8.6% gross species composition), followed by White Spruce (7.4%) and Subalpine Fir (6.1%). Overall, 30.2% of all rub trees were rare in their stand, demonstrating a significant selection for conspicuous tree species. The results of this study show that Grizzly Bears in SW Alberta rely primarily on well-used trails and uncommon tree species to ensure an increased probability of scent transmission.

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