“…Another obvious hypothesis is that, in most areas, the upper limits of tree vole distribution could be determined by the upper elevation limits of Douglas-fir, the primary food source of tree voles in most areas. of conifers such as Sitka spruce, western hemlock, grand fir, Monterey pine, and bishop pine in many low-elevation areas (Benson and Borell 1931, Clifton 1960, Jewett 1920, Kelsey et al 2009, Taylor 1915, Vrieze 1980, Wooster and Town 2002, this study). However, there are no records of tree voles feeding on mountain hemlock, Pacific silver fir, or noble fir, and we cannot rule out the possibility that these high-elevation species are unacceptable as a substitute for Douglas-fir as a food source.…”