Abstract 283 – Huckleberry habitat and its importance to Cabinet-Yaak and Selkirk Ecosystem grizzly bears (Ursus arctos)

Justin Teisberg, Wayne Kasworm, Michael Proctor, Thomas Radandt, Jennifer
Fortin-Noreus, Hilary Cooley

Huckleberries (Vaccinium spp.) are a food of nutritional importance to grizzly bears (Ursus
arctos) within interior populations of North America, providing sugar-rich calories in the late
summer and fall seasons prior to denning. We developed a resource selection function of high-
quality huckleberry habitat important to Cabinet-Yaak and Selkirk grizzly bears, using field-
verified huckleberry foraging radiolocations acquired during prime months of huckleberry
fruiting (July 15 – September 15, 2010–2019, from 22 female grizzly bears). Stepwise logistic
regression analysis identified 12 significant variables in predicting huckleberry habitat
important to female grizzly bears; all were included in a predictive model (Somers’ D = 0.729; K-
S statistic = 0.570, P < 0.00001). Most influential variables (P < 0.00001; positive [+] or negative
[-] relationship) include canopy closure (-), moisture deficit (-), time since last wildfire (-), solar
radiation (+), snow water equivalent (-), and growing degree days above 5°C (-). On average, 28
percent of an adult female annual home range includes predicted huckleberry habitat (x̄ = 61 ±
6.4 [SE] square kilometers). Seasonal ranges of females overlap extensively within predicted
huckleberry habitat, and degree of overlap trends with quality of habitat. Mothers and
daughters display similar selection patterns for predicted huckleberry habitat, suggesting
huckleberries are an important component to range expansion of these populations. Using
energetic predictions of huckleberry foraging in these areas, we find that a smaller average
body size of Cabinet-Yaak and Selkirk adult females (x̄ = 94 kilograms lean body mass) lessens
the energetic constraints of a huckleberry-dominant diet and may be a direct outcome of
huckleberries being a primary food resource for these populations.