Although the bird list for Dry Tortugas National Park currently contains 299 species, the area provides long-term habitat for few birds. Fewer than 40 species are typically present in winter, and only 7 species nest in the area regularly. Most species are transients or strays, present only briefly during spring and fall migrations.
Northbound migrants arrive as early as mid-February. Spring migration increases substantially during March and peaks during April through mid-May, with more than 200 species passing through the area. The largest concentrations are typically observed during the worst weather conditions, when high winds, rain, and cold temperatures ground the greatest number and diversity of migrants.