mammals include pika, hoary marmots, and martens. Glacier has 235 observed bird species, but the majority are migratory and only seen in the summer months. The 30 species who are year-round residents include woodpeckers, golden eagles, owls, ravens, Steller's jays, and golden-crowned kinglets. Unpredictable explosions of pine siskins, sometimes reaching hundreds of thousands in number, will appear and stay year round, but be gone the next year. American dippers feed in the many waterfalls and cascades of the park. Climate Located within the Interior Wetbelt, precipitation is a major environmental factor in the area. The park straddles two prevalent weather systems, with warmer, wetter air from the Pacific meeting the colder, drier air of continental weather systems. The moist air is driven to higher elevations by the mass of the Columbia Mountains. The result is frequent rain and snowstorms, especially during winter months. The mean annual precipitation in subalpine areas is This contributes to the large icefields and glaciers that cover much of the park's high elevations. Rogers Pass can receive up to of snow over the course of a winter. The eastern edge of the park, along the Purcells, is in the rain shadow and is relatively drier. The area can see wide variations in temperature and weather due to the extreme topography. Winter temperatures in the Selkirks are moderate compared to similar elevations in the Rockies to the east, with summer average highs reaching the high teens Celsius. Rogers Pass has a subarctic climate (Dfc) or what might be called a subalpine climate with short but mild and rainy summers and long, cold, and extremely snowy winters. Precipitation is heavy and very reliable year round and peaks during the month of January. Avalanche control Maintaining the Trans-Canada Highway through the snowy Rogers Pass is a constant battle. Parks Canada works with provincial highways crews and the Canadian Armed Forces to keep the highway open as much as possible. Parks staff play both a research and prevention role by monitoring snowpack levels and predicting avalanche probability, as well as working with the Canadian Forces to trigger controlled avalanches. The Royal Canadian Horse Artillery operate 105mm Howitzer cannons, based at circular gun positions along the highway. The highway is closed to traffic, shells are fired at trigger points identified by Parks forecasters, and smaller, more controlled avalanches are started. Facilities Although the park sees over four million visitors each year,