Our spring migration roughly runs from mid March through mid May, with a very few birds outside those parameters. The general peak of the movement is around 20 April, which is why FeatherFest has the dates it has and the GOS builds around it.
Most wintering birds like waterfowl and sparrows leave before that time, which makes more resources available for a passage migrant looking for food. As a general rule, the more north a bird nests, the later it migrates, as the area needs to warm and have food available when males arrive to sing and find a home.
You will notice that most of the warblers that arrive early are ground feeders since our trees aren’t fully developed in March.
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