Evidence of autumn breeding in Red Squirrels, Tamiasciurus hudsonicus, in western Montana

Red Squirrels (Tamiasciurus hudsonicus) routinely breed biannually in eastern North America, but normally breed once annually in western North America. However, a postpartum estrus resulting in two breeding seasons per year has been documented within the maritime region of British Columbia. I present two accounts of Red Squirrel behavior suggestive of autumn breeding in Red Squirrels in western Montana, and supporting evidence from the literature suggesting that late-season breeding resulting from a postpartum estrus may occur periodically in Red Squirrels within the Rocky Mountains.