WHY cannot migratory birds travel across the ocean? For most birds, a flight of many hours is extremely difficult. And flying across the ocean would require them to stay in the air for several days at a time.
Therefore, even relatively small seas birds prefer to fly around the coastline or cross in the narrowest places, such as the Mediterranean between Sicily and Tunisia. Among other things, away from the coast, birds cannot check their course against landmarks.
Nevertheless, oceans are not an absolute barrier for birds. The Little Ruff is a record-breaking species, whose breeding population in Alaska crosses most of the Pacific Ocean to reach its wintering grounds in New Zealand.
