Birdhouses: What's Printed, What's Fact

Bird houses are beneficial for birds and provide entertainment for spectators. These houses have become important for the propagation of cavity nesting birds. Dead trees with holes are frequently scarce and in areas where dead trees are quickly removed, bird houses are essential.

When Richard moved to Central Florida in 1968, he lived a short drive from property owned by Florida Audubon. Someone suggested that he place bird boxes on the property. His father, an excellent carpenter, offered to make the boxes. Richard consulted many "how to" books about bird box construction and his dad started building. Other people contributed boxes so there was a variety of designs. The boxes at the Audubon lot were monitored for over 30 years. About 10 years ago, Richard began making boxes. Some are sold - that money goes to Orange Audubon. Other boxes go to schools, parks, or friends. We are able to monitor some of these boxes as well as boxes in our yard. As the years progressed, we've learned that birds can't read. When selecting boxes, birds don't always choose the box the experts say is the perfect, and only, size for them.

We address seven myths about nest boxes. Before you make or buy a nest box, consider the following.

1. Nomenclature - Take the term "bird houses." Residents in our boxes include: squirrels (flying and gray), various species of snakes, mice, bats, anoles, bees, wasps, raccoons, and opossums. We use the more appropriate term "nest boxes" for our boxes.

2. Height about ground - One of the first questions we are asked when discussing boxes is, "How high should I place my box?" My reply, "Place it just high enough so that when you climb the ladder you can easily open the top and take a picture." For my boxes the height is 9 to 10 feet to box entrance. The impetus for this article occurred when I read, "screech owl boxes should be 30 to 40 feet high. A friend had a screech owl nest is a box 7 feet off the ground. We have had many screech owls nest in our boxes.

"Everyone knows a purple martin box should be 10 feet plus high." Apparently the purple martins didn't get that memo as I have seen two martin nests in one wood duck box with the entrance 6 feet above ground.

"A great-crested flycatcher box should be over 8 feet high." A great-crested flycatcher nested in a 'bluebird box' with a hole 4 feet above the ground.

Fig. 1

3. Birds want a specific size box - "If you want a certain bird, you have to build a box for that bird's specifications." See the above paragraph on purple martins. We have raccoons and opossums in the neighborhood. I decided they should have a box. The floor was 10" x 10", the height 18", the hole 6". A great-crested flycatcher nested in it (Fig. 1). Some commercial boxes for red-bellied woodpeckers are 9 1/2" x 7 3/4" (Duncraft). What is the diameter of a hole made by a red-bellied woodpecker? Maybe 4" at most. I have had red-bellied woodpeckers nest in boxes as small as 3.5" x 5.5" x 10" (Fig. 2).

Fig. 2

4. Ventilation - "Without air vents, boxes can turn into bird ovens." (US Fish and Wildlife Service, Homes for Birds) Knowing heat rises I had trouble believing anyone would write this. I decided to put it to the test. The test showed the ventilated boxes were cooler by 0.9 degrees C. The experimental procedure and results are published in Florida Field Naturalist 36:3, p.64.

Fig. 3

While checking eastern bluebird boxes, with no ventilation holes, in central Florida, we found 4 young. They were in a 'bluebird' box but one was larger than the others (Fig. 3). A cowbird perhaps? I waited and as they grew feathers, discovered that all were bluebirds. Inquiring about the cause of the larger one, the best answer I received was, "it was the first egg laid and the temperature was hot enough to start incubation." Usually the female waits until the last egg is laid to start incubating them, so this one got an early start!

5. Hole: size and location - "if you want a specific bird, you need a specific size hole." The size of the hole will exclude larger birds, if squirrels don't enlarge it. But the size of the hole will not exclude smaller birds or other animals. We put metal flashing around our holes. Our Florida screech owls, smaller than northern owls, have nested in boxes with 2 1/4" holes (Fig. 4). 

Fig. 4

The recommended standard size hole for wood ducks is 4" x 3". I made that size at first, but using a drill is a lot easier than a jig saw. My holes are now 3.5" in diameter which is OK by the wood ducks (Fig. 5).

The size of the hole for the 'possum' box with the great-crested flycatcher nest mentioned earlier has a diameter of 6". One day as I was measuring the width of the box to put the hole in the middle, I asked myself, "Why the middle?" so I drilled the hole to one side. The result, birds laid their eggs on the side furthest from the hole.

6. Ladders inside the box - "Rough surfaces, both inside and out, makes it easier for the adults to get into the box and, when it's time, for the nestlings to climb out." For a wood duck, yes. No feathers on the babies. But most birds have feathers before their exit. Think like a mama or papa bird. If your baby can't get to the exit hole, do you really want it outside in the cold, cruel world? Better to stay an extra day or two and build those muscles. Adult birds fly directly to the hole, no need for rough surfaces or a perch.

Fig. 5

7. Roof - Many boxes are made with roofs nailed so the inside cannot be checked and pictures cannot be taken. Result, almost all of these boxes will be filled with squirrel nests. And no pictures taken. We check boxes late February or early March, primarily to remove squirrel nests.

Richard makes three box sizes - one with 6" side boards, one with 8", and one with 10" side boards. Tufted titmice, bluebirds, and flying squirrels prefer the smaller one, sometimes great-crested flycatchers and red-bellied woodpeckers. The medium size is used by screech owls, flycatchers, woodpeckers, titmice, and squirrels. The larger size is my "wood duck" box although not exclusively used by wood ducks.

I use a hinge for the roof with one screw near the front to prevent an animal, usually a raccoon, or heavy wind from raising the roof. To take a picture or clean the box, I simply remove the screw. We have opened boxes with side entrances. Richard doesn't make them. Once a screech owl egg rolled out. Splat! Another time a startled chickadee exited and kicked an egg out while doing so. I would like to see the reaction when someone opens the side and is eyeball to eyeball with a snake. The bottom of our boxes are secured with three screws, one in front and one on either side. If woodpeckers or owls nest in the box, the floor is covered with poop. Remove the screws, clean the bottom and replace.

Tufted titmice, great-crested flycatchers, red-bellied woodpeckers, and screech owls have nested in our yard - a 1/3 of an acre in a suburban neighborhood. Bluebirds and wood ducks have also used our boxes.

We have enjoyed our experience with nest boxes and hope you will place some in your area. Someone once asked Richard, "If I buy your box, will you guarantee I'll get a screech owl." "No," he replied, "but if you don't get the box, I'll guarantee you won't get a screech owl. And don't be surprised if some other critter takes up residence." After all, birds can't read.

For more information, contact Richard and Christine at catbird@cfl.rr.com.