I started by reading up on what makes a good screech-owl nest box. The optimal requirements are as follows; entrance hole 3" in diameter, floor size 8"x8", and floor to hole should be 10-12". Screech-owl boxes should be placed ten feet or more off the ground. One researcher found that an internal perch in the box was preferred, or at least helpful, because of overcrowding as the young grew.

In terms of habitat, in Colorado, the Colorado Breeding Bird Atlas found Eastern Screech-owls nesting most often in plains and foothill riparian areas which had large cottonwood trees. Also, birds were found in urban areas with large deciduous trees. The first screech-owl I ever saw in Colorado was using a nest box in CSU Ornithology Professor, Dr. Ron Ryder's backyard. He had a modest backyard in an older section of Fort Collins, but it did have large trees. I have also seen screech-owls in Colorado using a wood duck box mounted low on the edge of a pond with no trees anywhere close, not an "ideal" location.

Owl Box in Tree ©Steve Frye Click to Enlarge

My yard has several factors going for it, but it is not "ideal" in terms of screech-owl habitat. On the positive side, my neighborhood is relatively birdy. I have seen 101 species from my backyard, and many of those have visited the backyard. My neighborhood is about 40 years old with large lots by suburban Colorado standards. It does have large trees, but many of the oldest cottonwoods have died in the last few years and have been removed. It is not in a riparian area, but we are about a quarter of a mile away from McIntosh Lake in Longmont.  Another strike against my plan is putting the nest box in a pine tree, which are usually notselected by screech-owls. That may be a result of more suitable cavities in deciduous trees rather than any aversion to pines. Of course, my cavity (i.e. nest box) will be suitable, but still placed in a pine. As we say at the Wild Bird Center, 'the birds don't read the books', meaning anything is possible. So I crossed my fingers and forged ahead with my plan.

Years ago my friend Malcolm gave my some old hollow logs he came across in his tree trimming business. I've had them in storage and have always thought of turning them into bird houses or planters. My owl boxproject was the perfect use for the largest log. This log was amazing because it was almost completely hollow. I used a chisel to remove additionalrotten wood on the inside and ended up with an 8" diameter interior space. After hollowing out the log, I attached some cedar boards to make the floor and some more to make the roof. The log wasn't exactly cut 'square' so I worked with its funny angles because I needed all the length in order to optimize the dimension for attracting a screech-owl. As you can see from the photo, the box has a sloped bottom and a funny two part roof.

As with any nest box, it is important to provide drainage and ventilation. The slope of my box floor works perfectly for drainage. If any water gets in, it will simply run down to the front of the box and out the drainage hole. A sloped floor might seem uncomfortable or down right impossible when it comes to incubating eggs, but screech-owl boxes should be filled with a couple of inches of wood shavings on the floor. I figure this will level the floor. I don't have any ventilation holes low on this box, but I figured with the large entrance hole, two part roof, and shady afternoon location that this box is sufficiently ventilated and will not overheat. I added both an internal perch and an exterior perch by drilling a hole in the side of my box and running a stick through it. Screech-owl mates like to perch near their nest so the exterior perch will provide a good place (and it's on the eastern exposure). Itis not recommended to add a perch to the entrance hole of a nest box. This is thought to increase the chances of predation by other birds or mammals. However, birds love perches near nest boxes and I think they are a great addition, just keep them away from the entrance.

Owl Box ©Steve Frye Click to Enlarge

To mount the box in the tree I attached two webbing straps to the back of the box. The box, with its sloped floor, will rest where a branch was removed and the straps should protect the tree from damage and expand some as the tree grows. Finally, I applied some spar varnish to the roof and the outside of the box. This should keep the box in good shape for years to come and it will not bother the owls.

As I finished constructing the box, I came to realize that the next step would be mounting the box way up in the tree about 24' off the ground. As I have grown older I have become less and less comfortable with heights. Maybe it's because I fell off a ladder onto the sidewalk a few years ago stringing Christmas lights? Anyway, my next internet research project was ladder safety. I dug little holes for my extension ladder to rest in so that it could not move and was level. I also strapped the top of the ladder onto the tree and came up with a system to tie myself onto the ladder. That way, I figured, when the fire department came both the ladder and I would be dangling from the tree. One my first ascent, the ladder was quite wobbly so I set about to stabilize it. I used a step ladder propped up against my extension ladder and tied on a 2x4 tripod that I use for lifting heavy rocks further up the ladder. This ad hoc system worked well, but it looked frightful. After all the adjusting, I was ready to mount the box.

I had rigged up a pulley system so I didn't have to ascend the ladder carrying the heavy box. It worked great and I was able to position the nest box without holding onto it. To attach the straps on the back of the box one needs to use both hands, thus leaving no hands for holding onto the ladder. It was a little nerve-racking given the strong winds and swaying tree. I was able to get the bottom strap mostly set, and then it was time for the upper strap. In order to reach the upper strap, I would have had to climb up a couple more rungs of the ladder and be standing mostly above the top rung. If I would have fallen, my harness system would have caught me, but at what price? I remained at the top of the ladder a while contemplating my next move before I climbed down and reached for the phone. As Dirty Harry would say, 'a man's got to know his limitations'.  

Preparing to Attach Owl Box ©Steve Frye Click to Enlarge

I called Jamin at Parker Tree Service and asked him to come out and finish installing my owl box. He trims our trees and I knew his skill set and equipment are far superior to mine. He finished the installation without incident and I'm sure much better than I would have.

Now I just have to wait for my owls to show up. As the box was sitting on the grass in my backyard, two starlings showed up and were happily going in and out of my owl box. Starlings are unusual at my house and I hadn't thought about them using the box. Indeed, starlings are only one of the species that might want to live in my owl box. Kestrels, squirrels, and possibly flickers would find this abode to their liking. I'm not sure that I can do anything about squirrels using the box. Any relocating or discouraging I think would be futile. Besides, theoretically,a screech-owl should be able to take a squirrel. They have a very fierce reputation, but extracting a squirrel from a cavity nest would be difficult at best. Sometimes in the natural world it's finders keepers.

Other native birds using the box would be fine with me, but I would have an issue if the European Starlings moved in. It's really no fault of their own, they are just being starlings, but it is unfortunate that they were brought over to North America. They have had a negative impact on many native cavity nesting birds because of their aggressive takeover and defense of available cavities. One strategy you can employ to discourage the starlings from taking over large nest boxes such as owl or flicker boxes is to use an alternate nest box. The alternate house should be smaller (more in keeping with starling needs), with a smaller hole (1 ¾") than a flicker box. You should still mount the box near the other one because you want the starlings to move into the smaller box and still defend the larger one as part of their territory so that other starlings won't use it. This will keep your large box available for its intended occupant. If you still don't want to raise starlings, just coddlethe eggs they lay in some hot water for a few minutes and return them to the nest. The parents will incubate these damaged eggs throughout nesting season and no young will be produced. If you remove the eggs instead of coddling them, the parents will lay another clutch.

Owl Box in Tree ©Steve Frye Click to Enlarge (Note: Look closely to see if you can spot the owl box in the enlarged photo.)

Territorial behavior and nest site selection for eastern screech-owls in Colorado happens in the first part of the year. Egg laying follows that period sometime in March. My box may have been placed a little late for this year's nesting attempts, but I'll still keep my fingers crossed. Atlas workers found fledged owls from late May to mid-July. This suggests a highly variable pattern of nest timing in Colorado Screech-owls.

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