The Refuge participates annually in the Stevensville Christmas Bird Count and has listed over 55 species for the count over the last several years; the key group found are birds associated with water. Looking for and identifying mammal tracks in the snow can also be productive and fun. Don't forget to look for colorful plants that do not flower in a traditional sense or season of the year, i.e. lichens. Winter wildlife watching is of course more difficult, but offers different opportunities given climate realities.
Wikipedia has summary winter climate data for Missoula as follows: a) the monthly daily average temperature for December is 23.9 °F (−4.5 °C) b) there is an average of 45 days where the temperature does not rise above freezing, and 7.8 days with sub-0 °F (−18 °C) lows annually. December and January have the least amount of sunshine compared to the other months.
Natural flows in the Bitterroot River decline from spring peaks throughout the summer and remain relatively stable through winter. Climate data for Montana show a slight reduction in annual precipitation and increases in temperatures over the last 100 years (National Climatic Data Center 2011). Climate change impacts predicted in the Rocky Mountains are rising temperatures, less snow, less water in snowpacks, earlier spring snowmelts, and lower streamflows in the summer.