From the Purple Martin Conservation Association's website:
Today, east of the Rockies, Purple Martins are the only bird species totally dependent on humans for supplying them with nesting sites. And they have been managed by man longer than any other North American species. If humans were to stop supplying martins with homes, they would likely disappear as a breeding bird in eastern North America.In 2003, the NY Times reported that this seasonal purple martin colony here in Annadale and another a bit further south down the Staten Island shore were the only two in the city.