We put the gourd tree up in February. We had a scout come by and check it out the first day! As of today, March 29, 2013, we have at least 10 purple martins that have taken up residence in our gourd tree.
The males are darker than the females. See the pair top left below for a comparison.
The gourd tree is right by the garden. It is so nice to go out in the evening and hear their trilling song and see them glide in and out of their houses.