Purple Martins are migratory birds, with the range of their migration pattern extending from northern Argentina at the south extreme to a wide band stretching across southern Canada at the north extreme. Depending on the time of year (see Time Frame), they can be found at most points in between.
The migration of the Purple Martins is tied up in their reproductive cycle, and they come to North America to nest and lay eggs. However, they do not always return to the same nesting site each year, and may move if they find something unsatisfactory about an old site.
East of the Rocky Mountains, Purple Martins are entirely dependent on bird houses and other forms of human construction. West of the Rockies, they are attracted to abandoned woodpecker nests, gourds and bird houses.
The main reason a Purple Martin will not return to an established nesting site is because it has been occupied by another species. Starlings and sparrows sometimes beat Purple Martins back to their established colonies, stake a claim and drive off the martins.
Good Bird House
A good Purple Martin house is painted white or a light color to create a cooler interior. The box should be 7 inches wide, 12 inches long, and 5 to 7 inches tall, with a 2-inch-wide entrance hole about 1 inch off the floor.
In North America, Purple Martins do not make their first appearance in Florida until around Jan. 15. By mid-March, they will be in a band stretching from the Chesapeake to Kansas, and they reach their northern extremes by early May.