Abstract 268 – Female grizzly bear dispersal and range expansion in the Yaak River of northwest Montana

Wayne Kasworm, Thomas Radandt, Justin Teisberg, Tyler J. Vent, Michael F.
Proctor, Jennifer Fortin-Noreus, Hilary S. Cooley

Female grizzly bear (Ursus arctos) dispersal and range expansion is critical to
recolonization of former habitat. Female dispersal is typically of shorter distance and therefore
slower than males but necessary for establishment of reproducing populations. Telemetry and
genetic detections in conjunction with trail camera photographs were the basis for establishing
generational minimum convex polygons. We defined four generations of female grizzly bears
arising from a single female in northwest Montana to determine amounts and rates of female
dispersal and range expansion. The data set included detections from 24 individual female
bears from 1986–2023. The single female that produced this matriline appears to be the only
successful female in the area indicating a very low-density population in 1986. Female range
expanded from 853 km2 to 4,146 km2 during the 38-year window of calculation. The eight
cardinal and intercardinal directions from the initial female centroid to the perimeter of the
cumulative convex polygon ranged from 23.8–50.1 km with a mean of 34.8 km. The rate of
expansion based on the cardinal and intercardinal directions averaged 0.9 km per year and
ranged from 0.6–1.3 km per year. Greatest rate of expansion appeared to be associated with
least human habitation.