For the 2013 purple martin season, I have largely kept the same housing composition with one main modification. I have replaced a system with two modified Sunset Inns comprised of 16 compartments and 12 Super Gourds and Troyer Verticals with a new gourd rack of 24 Troyer Horizontals with tunnels/porches.
My colony consists of 22 systems including 18 gourd racks of various styles and sizes, two multi-purpose poles with two modified Trio M-12s and two WatersEdge houses, and two 12-room Trendsetters. There are 344 gourds: Super Gourds, Excluders, Troyer Horizontals with cling plates and with tunnels/porches, and Troyer Verticals with tunnels/porches. I have six aluminum houses as mentioned previously and these comprise 44 compartments. So my total number of cavities for 2013 is 388. In 2012 I had 392 so a minor decrease of four cavities.
All housing has round holes, pre-nests of pine straw, and can be raised via a brake winch or rope/pulley system. I must admit that I prefer the winch over the rope/pulley and may eventually convert to all winches.
Every system is protected from rat snakes with a net trap made from bird netting. These traps readily catch most rat snakes that try to climb the poles and we have caught some huge ones.
In 2012 I attracted 347 pairs of martins and raised a BUNCH of youngsters. We had plenty of rainfall earlier in the season and the parent martins were able to find sufficient food to feed their young. In fact 2012 was the best purple martin season I have ever had. In 2011 we had a disastrous drought that resulted in a huge decline in flying insects, particularly dragonflies and many martin nestlings/fledglings starved to death.
Here are some photos of my purple martin colony for 2013:
This photo shows a section of my colony site.

This photo shows another section of my colony.

This photo shows yet another section.

This photo shows the entire colony.

Steve
