Winter is a quiet season for birds in Alaska. Most migrate south to wintering areas in the Lower 48, Mexico, South America, and Polynesia. But, some species remain in Alaska through the winter. Even in the northernmost regions of Alaska, some ravens, snowy owls, and gyrfalcons remain, and offshore, murres and a few gulls linger near openings in the pack ice. Over 25 species endure the harsh winters of interior and western Alaska, and over 100 stay through the milder coastal winters of southcoastal and southeastern Alaska.
Tree cavities are formed by tree disease and decay and by woodpeckers. All six woodpecker species in Alaska excavate cavities for nesting and roosting. Most other cavity_nesting birds use abandoned woodpecker holes. Usually a pair of woodpeckers excavates a new hole every year. Before selecting a final nest site, a pair may start, then abandon, several holes. During fall, overwintering woodpeckers also excavate cavities for winter roosting. However, woodpeckers are only able to excavate holes in dead or decaying trees.