This is a jumbo natural gourd that I've modified with an new excluder entrance.
Construction materials include:
4" PVC cap
excluder plate from PMCA
1/4" wood cut for porch
hinges and machine screws
Before providing full instructions on how to make this modification,
I'll let the purple martins decide if they like it or not and let you know later in 2002.

 

View my pictures from the 2001 season (purple martins and 5 babies)