Is Tree Swallow migration north similar to their migration south?
As the daylight hours lengthen in late winter and temperatures moderate once again, internal hormonal changes stimulate movement of Tree Swallows back toward their nesting grounds. However, migration north is different. For one thing many of the swallows that began the move south last year have perished. And instead of autumn’s great flocks, surviving Tree Swallows head north early in spring as individuals and small groups, older swallows migrating first, followed a few weeks later by second-year birds. And rather than a slow step-wise progression from roost to roost, northern migrants fan out across the continent rapidly until they reach their nesting grounds. Migrating north as early as Tree Swallows do can be dangerous. Flying insect food and even berries may be scarce or absent, and death from starvation and hypothermia is a very real risk. Marty Burke’s photo below shows a flock in Ontario halted by cold weather during the first part of April. Note how the swallows have huddled to
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