During the brief arctic summer, the North Slope is home to millions of birds. Many come to nest and raise their young. Others come to molt or simply to pass through on migration. A few species are present year-round. Rock and Willow Ptarmigan are the most abundant birds during winter and are found in patches of willows where they feed mainly on the buds.
Ravens are the most conspicuous winter birds.
A few Gyrfalcons and Snowy Owls may also be present, depending on the abundance of prey. Some of these stay in ANWR, while others continue to destinations elsewhere in Alaska and Canada. Those that do stop congregate wherever bare ground or open water may be found. River deltas, flooded by meltwater, and shallow ponds are heavily used at this time, as are patches of snow-free tundra. As spring progresses, the birds disperse to occupy suitable habitats.