Purple martins only eat flying insects, therefore, they must migrate in the fall to a place where there is an abundance of food during our winter months. All martins fly south of the equator to Brazil. They do not mate up there (reproduction only takes place in North America). While there, they molt all of their feathers. Male purple martins between their 2nd and 3rd year of life undergo a dramatic plumage change as they reach full sexual maturity. The new purple feathers are what gives them their common name - Purple Martins.
Shortly after winter solstice in December, purple martins start their migration back to North America. Unlike most migratory birds, though, the martins do not fly as a flock but instead fly back as individual birds. The migration map shows the approximate dates the first martins start showing up at established colonies.
The older ASY (After Second Year) martins almost always return to the same bird house they used the preceding year. This is known as nest-site-fidelity. The younger SY (Second Year) martins stay in Brazil for 6-8 weeks longer than the older martins, so when they return back to the house they were born in, it is already full of the ASY birds (the SY's now have to find another housing system to live in). This is why many landlords will put up additional housing systems every few years.
The female martins lay one (1) egg a day, but don't start incubating them until the last egg is laid. It then only takes sixteen (16) days for the eggs to hatch, all on the same day, usually. Both the male and female will now spend the next thirty (30) days catching whole insects and bringing them back to feed their young. Then the young will all fledge the nest and be on their own.
It is OK to raise and lower your purple martin housing system even with babies in the compartments. The adult birds will get accustomed to your doing nest checks to make sure everything is going according to plan. Some people even number the gourds to keep detailed records of how many eggs are laid and how many grew up to fledge from their housing system.
After the purple martins leave in the fall, bring the gourds down and clean them out. All that is required is for you to break up the solid nesting material and dump it out. You DO NOT need to wash and scrub the insides. Studies indicate that the older martins, the ones that raise the most young, actually prefer dirty interiors.
As you can see, it really is easy to establish and maintain a purple martin colony. For some reason, there are web sites out there trying to make it a complicated endeavor. Watching your colony return every year gives you a sense that there is a way for you to help out our natural environment (even if you live in a city). The male below and PM Propagators want you as a landlord.