Purple Martin Range & Migration Map
The breeding range of the Purple Martin is shown in gray. Horizontal lines mark average arrival dates of older martins at established colony sites. Yearling martins, the age-group that typically colonize new breeding sites, don't begin arriving until 4-6 weeks after these dates, and continue arriving for an additional 4-6 weeks in the north, 10-12 weeks in the south. This means martins can be attracted to new housing through mid-May in the south, mid-June in the north. New hobbyists should not open housing until 4-6 weeks after the dates shown here. Opening earlier at new sites will result in the attraction of nonnative, nest-site competitors (House Sparrows and European Starlings), instead of martins. West of the Rocky Mountains, Purple Martins have different nesting habits. In the southwest martins nest only in old woodpecker cavities. In the Pacific Northwest, martins use gourds and single boxes, but not multiple-room houses.
Credits to Purple Martin Conservation Association (PMCA)