The Purple Martin is one of North America's best loved birds. People have a long history of providing housing for the Purple Martin. Even before the European settlers arrived, some tribes of Native Americans would hang up empty gourds to provide housing for them.
The Purple Martin is a social bird that lives, breeds, and migrates primarily in colonies. Thus, their housing requirements a bit different than other species of birds. Eastern Purple Martins require "condo" style group housing such as this Purple Martin house for their colonies.
In any case, Purple Martins do not need feeding. They are strict insectivores who eat insects while in flight. But Purple Martins, especially in the Eastern part of North America are very reliant on human-provided housing. Luckily for them, there are thousands of Purple Martin lovers all over just waiting for their yearly arrival (usually in May).
Putting up a Purple Martin style birdhouse and making sure it is free of other competing birds (such as house sparrows and starlings), will ensure that you can provide a backyard habitat for these delightful birds.