One question I get a lot is, "Are Owl Guards really necessary on martin houses?"
The answer is "Yes", they are!
I live in an area where Great Horned (and Barred) Owls are very prominent and since they do their dirty work at night...when I'm asleep...I'd never see or catch them, so I use owl guards on my houses to protect my martins. Owls can be a very destructive bird to a martin colony. They are big, very strong and can literally rip some housing apart to get at its contents. And yes, owls are everywhere throughout the entire martin's range. An owl that gets successful just one time will return time and again and within just a few nights, will decimate a martin colony and I worked too hard to build my colony to let an owl destroy it. Owl guards are just too easy and inexpensive to build and add to the houses to not spend a little time to give your martins a little more protection from these night time marauders.
3/4" diameter dowels. (Yes, 3/4" Owls are very strong and will tear smaller ones apart).
Depending on the type or style of house you have, you'll have to figure out how many you'll need.
A quantity of 3/4" thick lumber. Enough to make the plates shown below that will fit your own house.
A quantity of 1 5/8" self drilling decking screws.
Believe it or not, there is only one part that is required to be made. (I said they were simple to make). You'll need to figure out what kind of plate will be required to add these to your own style house. I've shown both a T-14 and my own house so you can get an idea of what I mean. Both of the plates for these two houses were different and your house may be even different, still. I've given an idea of what to do below on the plates that go on my own house, you'll just have to adapt the idea to make them fit your house. For the T-14, they are basically rectangular (8 1/2" wide x 6" deep) and have half holes that mount 2 vertical dowels that go up the house in front of the nesting compartments. For a normal T-14, you'll need 18 of them.
If your house is different, then you'll first have to figure out how to fit them to your house.
Take a look at the photo below, It's my own house design. The plates for it are 31" long x 6" deep, and have a number of dowels across the front in order to get protection in front of each set of holes. I've shown the distance on the marked plate (5 1/2") that should be between the dowels, and this will apply for any style house. This distance allows the martins easy access while at the same time, hindering the much larger owl from gaining access to the house and a set of these will be required in front of each compartment of the house. This style house only requires 2 plates per side, each placed directly under the entrance holes. The dowels can extend up to protect the upper holes.
Since all of the plates for the T-14 are identical, I'll show you an easy way to make them 2 of them at the same time. They need to stick out away from the house at least 6". This will locate the protective dowels 6" out from the house. Yes, they need to be this far out. Great Horned Owls are very large and heavy birds. What the dowels do is prevent the owl from getting close enough to the house to do any damage. Plus, the vertical dowels make it harder for the owl to hang on. Yes, his/her claws would dig into the wood making it easy for the owl to hang on, but it would take both feet to make the owl stable and if both feet are being used, there aren't any left over to get at the martins. The trick is to make it as difficult as possible for the owl. If it is not successful in easily gaining food, it will quickly go somewhere else if search of easier prey and that's what it's all about.
Dowels can be found at just about any local hardware store, lumber supply house or home center. Usually they'll be made of Birch and thus will require treating for out in the elements.
Or... if you have access to a router with a 3/8" round over bit, you can make your own like I did. I made my own because I used Western Cedar for my houses and I wanted the dowels to be of the same material. It's a great wood for out in the elements and just simply doesn't rot. And since I have a bunch of it laying around, it was an easy matter of cutting some 3/4" square strips and rounding them over to make the dowels. That's not to say you have to use the same wood. Pine or Cypress will work just fine also, However, the pine needs more care to prevent rotting over time. If you don't want to make your own, then they can be purchased.
I cut some strips of wood that were 6" wide. Then I cut them into 8 1/2" lengths (the same as the width of my T-14). I then marked the distance between the dowels (5 1/2") centered on the plate. I only drilled half holes in my plates. This allowed me to screw the dowels directly to the front of the plate without a whole lot of fuss. Plus, if I ever need to either repair or change one out, it's a simple matter of unscrewing the old one and screwing on the new one without having to remove the plate from the house.
To easily make half holes, first mark where the holes will go. Then simply clamp the 2 boards together and drill the holes directly on the line where the two boards meet.
It's much easier to drill the holes this way. It gives you a nice clean hole and once you take them apart, you have nice clean half holes in your plates.
Once you have your plates made, it's a simple matter of adding them to the house.
Take one of the plates out to the martin house. Hold it in place where you want it to be (The top of the plate needs to be 1/4" below the bottom of the entrance hole) and using a pencil, simply scribe a line on the top and bottom side of the board. Now pre-drill the clearance holes in the center of these two lines. Then, determine how many you want from side to side and space them equally. I used 2 on the T-14 and 4 on my own house. Do this for each plate, including the top plate.
Now, simply hold your board up to the front of your house door. (Wood clamps work wonders in this case)! Take a drill with a driver in it, some decking screws and screw from the back side of the house door and into the edge of the board. 3/4" lumber is wide enough it won't easily split. Again, do this for each plate.
Now that you have all the plates screwed to the house, its just a matter of adding the dowels.
Take a look at the photo at the top of the page. Set them in place where you want them to be. Mark and cut them them for length, (mine are the same length as my doors). Mark and drill holes for screws in the center of each plate. Now, it's simply a matter of screwing the dowels into the front holes of the plates. Don't overdo the screwing. If you have a drill that you can set the torque, use it so they won't split.
I added mine individually to the house. I felt is was just easier to be accurate that way. However, now that they are all screwed together, they can easily be removed from the back of the door for ease of painting and then replaced after the paint dries.
Done! Now wasn't that simple?
All wood on a martin house should be painted. As you can see, I decided to simply paint mine white, and then include the color of my trim around the edges of the plates.
The colors and how you do it will be your choice of course, and you can do as you wish.
You now have a good measure of protection between your martins and nighttime marauders and some extra peace of mind when you go to sleep at night that your martins are a little safer.