Migration Info During winter, Red-eyed Vireos are most numerous in the northern Amazon basin where they feed primarily on fruits. As the time of migration approaches, they begin to consume more insects. Whether or not a bird crosses the Gulf may be diet-related. Birds with substantial fat reserves are more likely to attempt a crossing; individuals lacking adequate reserves tend to orient northwestward and follow the coast. This species seldom stays for more than a day along the U.S. Gulf coast; most individuals continue their migration at first nightfall. This may be an adaptation that allows Red-eyed Vireos to avoid the intense competition for foraging habitat that is in such short supply in this area. This is one of the more common "eastern" species to appear as a vagrant along the California coast in late May and early June.