In my aluminum purple martin houses, heavy prolonged rainfall may intrude into the compartments and wet the nesting material. I have seen this happen particularly in my Trio houses with flip-up door panels because there are open slots between the door and floor. This can also occur with any house where the door panels are separate and can be opened to inspect the compartments. My Sunset Inns have removable door panels and rainwater can seep under the panels and invade the nesting area. Rainwater hits the porch, then seeps under the door panel and eventually wicks up into the nesting material.
Probably the best way to minimize or prevent most rainwater saturation of nests in aluminum houses is to use nest trays. Nest trays isolate the nests and keep them off the compartment floors which can become wet. I use nest trays in my two Trendsetter houses and these trays have kept the nests dry for the most part.
Trio offers aluminum sub-floors which are placed on the compartment floors and the sub-floor attempts to elevate the nest ABOVE any rainwater that seeps into the nesting area. The sub-floors do have holes to allow any rainwater that may blow through the entrance holes to drain out. I have used these sub-floors and they do help but the nests can still become drenched and water may wick up from the compartment floor through the drain holes in the sub-floors.
For the Sunset Inn houses, there are wiremesh sub-floors that can be placed in the compartments to provide a better foundation for nests and eliminate splay leg syndrome for nestlings. If a small nestling rests on bare slick metal, the nestling may develop deformities in its legs due to constant slipping. Also the wiremesh helps keep the nesting material off the compartment floor where rainwater may seep in. These wiremesh sub-floors will fit in the Trendsetter houses too, but there are specially made nest trays that are probably more appropriate.
I recently purchased from the PMCA 24 new nest trays for my two 12 room Trendsetters and enough wiremesh sub-floors for the 16 compartments in my two re-built Sunset Inns which had been severely damaged by the April 26, 2011 storm. The wiremesh sub-floors have been greatly improved over some of the first ones I had. The new wiremesh sub-floors are made from relatively thick black metal and don’t have any sharp points. I like them a lot.
For a number of years I have been using asphalt roofing shingles in conjunction with any sub-floors in my various aluminum houses where I don’t have nest trays. In the past I have even used the shingles without any sub-floors in several of my Lone Star Goliad houses.
These shingles serve several purposes. First, the shingle has a coarse surface and this may provide a better platform for nesting material and helps keep it from spreading apart. Nesting material easily separates on a slick metal surface as the female martin creates her nest bowl. This may result in eggs/babies resting on slick bare metal.
Second, the shingles can be easily cut to fit over any sub-floor, including the Trio metal one and the Sunset Inn meshwire floor. The shingle helps to keep rainwater from wicking up underneath any sub-floor with drainage holes or a completely open one like the wiremesh.
In my Trio M-12s, the compartments are enlarged to 6” x12”. I simply place two Trio metal sub-floors in the compartment and then place a piece of asphalt shingle that fits nicely over both. The shingle keeps the Trio sub-floors from coming up and prevents most rainwater that seeps underneath the sub-floors from wicking up through the drainage holes into the nest. However, I still have some problems with heavy rainwater blowing through the entrance hole and drenching the nest. But I believe the shingles have worked in conjunction with the Trio sub-floors to minimize saturation of the nests under most situations. And the rustic surface of the shingles helps keep the nesting material from sliding apart.
For my Sunset Inns, the wiremesh sub-floors fit somewhat loosely inside the compartments so that it is easy to remove them as necessary. There is about a ¼ of inch of distance between the wiremesh and floor. Any rainwater that seeps in would flow under the wiremesh and not contact with the nest. However, any nesting material that protrudes through the wiremesh and touches the compartment floor may still wick any moisture up into the nest.
Just like with the Trio sub-floors, I place appropriately sized asphalt shingles over the wiremesh and this action blocks any rainwater from wicking up underneath. Of course, some rainwater can still blow through the entrance hole, but this water would be confined to a smaller area not directly in the nest bowl.
Asphalt roofing shingles are easy to cut and I use large tin snips. You could use a knife or other cutting instrument. I simply cut out a shingle to match the dimensions of any sub-floor I am using. For my Sunset Inn wiremesh sub-floors, I generally cut the shingles a little larger to cover as much of compartment floor area as possible.
Using asphalt roofing shingles with various sub-floors or even alone may help to minimize nesting material from spreading apart because of the coarse shingle surface. On slick metal, nesting material may not stay together and when the female martin creates her nest bowl, the material may slide around. This can leave bare metal in the nest bowl where the eggs are laid.
And asphalt roofing shingles when placed over sub-floors can help prevent rainwater from wicking up through any drainage hole or open areas into the nest. However, during blowing rains or prolonged deluges, rainwater may still enter the entrance holes and drench nesting material in that immediate area. But in many situations, the shingles may help keep the nests drier.
Here are some photos of an asphalt shingle being used on top of a wiremesh sub-floor in a compartment of one of my Sunset Inns.
This photo shows a PMCA wiremesh sub-floor inside the compartment of one of my Sunset Inns. This is an improved model over the earlier one. The wiremesh is thick and coated with a black enamel like substance.
This photo shows an asphalt roofing shingle cut to fit over the wiremesh sub-floor. I made the shingle a little larger than the sub-floor to provide more coverage.
This photo shows a pre-nest of pine needles constructed on top of the shingle. I made this nest before we had nearly two days of heavy rains. After the rains, I check the nest and it was largely dry except for a little moisture in the pine needles in front of the nest hole. Apparently some rain managed to blow through the entrance, but it did not completely saturate the nest.
Steve
