Robins are the famed harbinger of spring, and the vast majority of these songbirds leave Alaska for the winter and return in the spring. But a few robins stick around every year and overwinter in Alaska.
The winter diet of robins is mainly fruit. If there are shrubs and trees like mountain ash available with a good crop, robins will stick around until the food source is depleted. Temperature plays a more minor role on whether or not robins remain in northern areas. Prolonged cold requires more energy for the birds to stay warm, so they might exhaust the food supply sooner and move on. If the ground is bare and temperatures are fairly warm, robins will forage for invertebrates much as they do in the summer, so they tend to move out of areas with snow on the ground.
The proliferation of fruiting ornamental shrubs in urban areas may be contributing to what appears to be increased numbers of robins spending at least part of the winter in northern areas.
The Great Backyard Bird Count is an annual citizen science project that takes place over four days in mid-February, providing a snapshot of the North America's wintering birds. Robins are present in winter in Alaska every year in small numbers, and in 2011 more than 100 were seen in Homer, with about a dozen present in both Sitka and in Juneau. In February of 2009, 40 robins were found overwintering in Anchorage.