Northward Fall Migration on the Atlantic Coast and Its Relation to Offshore Drift

Abstract

Recent observations of fall migration at Nantucket Island, Massachusetts, and Block Island, Rhode Island, have shown that many nocturnal migrants pass rapidly through the islands and leave in a north or northwest direction during daylight hours. Similar diurnal movements of night migrants to the north or northwest have frequently been observed at other places along the Atlantic coast from Virginia to the Gulf of St. Lawrence: they have also been noted at sea aid at several places inland. southwestward movements of these species by day have been noted inland, but are very rare on the coast. Published and unpublished observations of these movements are reviewed in detail. We think that most of the birds that reach the outlying islands do so as a result of wind drift from migration routes over the mainland; there is as yet no convincing evidence for recent suggestions that the islands form part of the normal migration routes of these birds. The largest numbers of birds arrive after being drifted toward the coast by northwest winds, but northeastward movements also occur in southwest winds. The northwestward flight is interpreted as "redetermined passage," i.e., attempts by wind-drifted birds to regain their preferred migration routes. Some birds reorient northwestward while at sea out of sight of land, while others start their northward flight from points on the mainland. Drift over the sea appears to have been an important factor influencing migration close to the coast, and many of the nocturnal migrants that pass through the northeast appear to have developed other ways of avoiding it. In particular, many species seem to have developed migration routes a little distance inland, and their occurrence on the coast is mainly a result of drift. Some diurnal migrants appear to have similar adaptations.