Thanks, folks, for the replies.
The disease aspect of housing a colony of course is my primary concern. My henhouse will be approximately 200-250 feet from my gourd rack which isn't really that far in the big scheme of things since purple martins migrate thousands of miles twice a year. But, I've had the colony (16 gourd gourd-rack) for years so I guess it'll be staying. Thankfully, martins are not ground dwellers, they eat their meals on the fly (flying bugs) and even drinking on the fly. Basically the only times that they come to the ground is seeking grit or mating. The droppings are the big issue, but at least these are widely scattered or either more closely confined to the base of the gourd rack. It seems the martins normally defecate upon taking flight and within 100-200 feet of the rack...that leaves my propose henhouse right at the edge of this perceived dropping perimeter.
As for the myth of "eating their weight in mosquitoes"...nah, just a myth propagated by a less-than-honest "businessman" as a slogan to sell *his* martin houses. Purple martins might accidently eat a mosquito but they don't frequent the areas that mosquitoes do and are either just leaving the roost or going to roost when the mosquitoes start coming out in numbers.
MHF... How long have you had both chickens and martins?
fargosmom... Yelp, they are truely amazing flyers! A real joy to watch.
speckledhen... I stopped feeding wildbirds a few years ago and before then only fed niger and blackoil sf seeds. The cracked corn/millet mixes tends to draw in the weaver finches and starlings. Being as corn/millet is a big part of chicken mixes do you have a problem with these two rodent birds around your place? I'm curious as to whether I will see these birds suddenly start showing up once I start raising my flock. We have many poultry farms in the area and I see many of these flying rats hanging out at the big houses. Presently I have no foreigners, only native species that frequent the property.
Thanks for all of your replies,
Ed