American Kestrel Nest Box

The American Kestrel is North America's smallest falcon, and unlike its larger cousins, this beautiful little bird chooses to nest in cavities (i.e., holes in trees or other objects, such as utility poles and buildings). They will also accept artificial nest boxes placed in suitable habitat, which is open areas such as pastures and hay fields. This Instructable will hopefully help you construct your own safe and secure nest box that will also be easy to clean and maintain. The design is based on plans refined by Dr. John Smallwood and Richard Melvin for use in the difficult environment of Florida, and should be suitable for use everywhere.

This box is also suitable as is for screech owls, and could be scaled appropriately for a variety of other species (wood duck, bluebird, swallows, etc.).

Here are the dimensions of the cuts that you will need to make - feel free to reorder them in order to accommodate the quality of your lumber. You'd be wise to make sure important parts, such as the back, front, and top, are cut from board sections lacking cracks or knots.

This Instructable follows the order of steps that I used to construct my boxes, but you are free to mix things up in any way you choose. What seems like a logical and efficient workflow to me might not suit you well, and there are many ways to end up with a functioning nest box.

To start, it would be best to have access to a facility with a variety of wood-working tools, like serious saws, a drill press, and plenty of workspace. I was lucky enough to be able to use facilities at the University of Florida in Gainesville. It's certainly possible to make boxes with handheld equipment, so improvise if you need to.

You'll also appreciate:

A good quality cordless drill
hammer
straightedge
carpenter's pencil or pen
measuring tape
work gloves
safety glasses

For the drill, you'll need several sizes of drill bits (in my case, 1/8, 3/16, 1/4, and 1/2") and a Philip's head driver bit. Since you'll be switching between drilling pilot holes to driving screws, you will find a quick-change bit quite useful. If you do have access to a drill press, then a 3" hole saw will be quickest for cutting the entrance hole.

Hardware needed includes exterior grade wood screws, nails to form the door hinge, and larger duplex style nails to secure the door.

The most important component, of course, is the lumber. Never use treated wood of any kind. The best option is cedar, but in some environments, clear pine or whitewood will last for a few years. Each box will require a single board, 1" x 10" X 8'.

Depending on how many boxes you plan to build at one time, you might want to divide the construction process into stages. I had lumber for 38 boxes, so I opted to begin by cutting all of the pieces to size.

No matter what kind of saw you use, be sure to use proper safety procedures throughout - power tools are fun, but their improper use can be fatal! Here, I set up a brake at the proper spot along the bench to safely and consistently cut 22" pieces, which will form the back of the box.

Next I moved to cutting:

front pieces (14")
side pieces (currently both sides together, total of 25 inches)
bottom (7.75")
top (14")
and sill (4")
Save scrap for patching used boxes in the future.

The backs, bottoms, and sills can be set aside, but the remaining pieces need further work. The sides need to be separated by a non-right angle cut, so with the sort of saw that I had, I needed to measure and mark the appropriate cut, then change the rotation of the saw. Once set, I could tear through the pile of sides rapidly.

Now it is time to trim the top pieces. Since the top needs to have a slope to shed rain, the back edge of the top piece needs cut at an angle. In this shop I had a saw that was easy to adjust to cut at an angle, and I experimented a bit to figure out what this angle was. Since these are fairly small pieces, I used this special tool to push the work along rather than risk my fingers.

The last major cutting operation involves preparing the entrance holes on the front pieces. Move to the drill press, and set the hole saw up. Also, get the cordless drill set up with a fairly large (1/4") drill bit. Here you see how I've set a piece of waste wood on the press base so that the hole saw has something to bite into.

Next, measure and mark where the center of the entrance hole should be: 3" from the top of the front piece, and in the middle (5") horizontally.

Put the front piece onto the waste wood, and lower the hole saw into position, checking that it will hit your target correctly. Fire up the drill press, and lightly score the piece with the hole saw.

Pull the hole saw back out, turn off the drill press, and using the mark made by the saw as a guide, drill a few 1/4" or similar sized holes along the inside of that circle. The idea is to create exit holes for the shavings and sawdust made by the hole saw to escape into. This will reduce the friction involved in cutting, thus lowering temperatures and making the process go more smoothly. After the holes are drilled, put the piece back onto the drill press, check the alignment, and fire up the drill press.

Lower the hole saw, and take your time guiding it through the piece. The drill press will let you know if you're trying to force it too quickly, probably by blowing a circuit if you push it too hard.

Once you're through, lift the hole saw out, turn off the press, and clean the core out of the hole saw. I found it easiest just to pull the hole saw off the press and use a spare screwdriver to lever the chunk out, then reattach the hole saw for the next use.

Finally, all of your pieces should be ready for assembly. Move over to your work table, and get your cordless drill, drill bits, wood screws, nails, duplex nails, and hammer ready. You might want to quickly piece together an entire box to make sure that your pieces are all cut to the proper size. Don't worry, I'm going to show you how to put it all together in a way that doesn't require a helper or clamps to complete the job. Although if you're lucky enough to have a willing accomplice, the job will probably go more quickly with an extra set of hands.

Lay a back piece on the table. Prop up a left side piece, bottom, and sill on their proper places on the back piece. If you balance them correctly, they should stay somewhat stable. Rest a front piece on top of the assembled pieces. Perfect the alignment of the pieces, making especially sure that the side, front, and back are in good alignment. Drill four to five pilot holes in the front piece through to the side piece; in my case, the 1/8" drill bit was an appropriate size.

Without moving things, swap to the driver bit, and screw the front to the side piece using the pilot holes.

PILOT HOLES ARE KEY TO PREVENT SPLITTING DURING CONSTRUCTION!

Resist the temptation to fully sink the screws into the lumber - it is better to leave the heads out somewhat. This way, when the box swells and shrinks when exposed to the elements, the wood will be less likely to split.

Pause to check the alignment of the front piece and bottom, and once they're nice and square, drill several pilot holes through the front into the bottom, and follow up with screws. Proceed to do the same with the sill and the front.

Double check that all of the alignment looks good so far, and then drill pilot holes through the side piece into the bottom, then put screws in. Do the same with the sill.

Flip the entire assembly over so that it's laying on the front piece. Check that the box portion is more or less centered on the backing, and that the side piece is flush along the edge of the back. Drill pilot holes through the back into the side, then add screws. Put pilot holes through the back into the bottom piece and sill, and switch to screws.

Throughout the assembly process, do not scrimp with hardware. You might be tempted to save a few cents on screws, but it's more important to end up with a solidly constructed box. So make sure each piece is well anchored to its neighbors.

Now, set the box upright with the excess back plate over the edge of your work surface so that it sits level upon the bottom piece. Set the top piece in place, drill pilot holes through the top into the side and front, and attach. Flip onto front or let remain standing, drill holes through backing to the top (at a slight angle), then attach.

Lay the box on its back, and fit the door piece roughly in place. You want the door to not be snug, as later swelling might make it impossible to open. So if need be, trim a little bit off here and there. Drill a pilot hole in the lower outside center of the door, but not all the way through. Put a screw in, but not all the way - you're adding a sort of handle to the outside of the door.

Now fit the door piece in its place. Holding it steady, drill a pilot hole through the front into the door as close to the top of the box as possible. Put a nail into the hole. Flip the box onto its front, and drill another pilot hole opposite the first. Hammer a nail into that one, and now you have a hinged door.

Put the box onto its back again, and swap to the 3/16" bit. An inch or two below the hinge, drill a hole through the front into the door, but at an angle so that when the box is upright, the tunnel through the wood into the door aims downward (look at photo for better explanation). This will prevent wind and gravity from working the door pin out in the future.

Make the hole nice and deep, and then slide one of your duplex nails in so that it holds the door shut. The hole should be large enough that the duplex nail can slide in and out easily. Its duplex shape will help keep the nail from being sucked into the wood by wind action, as well as give you extra area to grab onto when trying to free it for the first check of the season.

Almost there! Still with the larger drill bit, put a half dozen or so drain holes into the boxes' bottom piece. Then along the upper part of the side, put a few ventilation holes. Finally, add holes in the backing piece to accommodate your planned hanging hardware. I actually ended up using a fairly large drill bit (1/2") to put pairs of holes above and below the box large enough to handle the extra-large zipties we use for mounting.

And that's it! Enjoy your lovely new nest box while it's still nice and clean! Then catch your breath and go back to your pile of lumber to assemble another. With practice, you should be able to piece together a box from pre-cut wood in less than 15 minutes.

If desired, you could paint the exterior of the box with non-toxic paint, but there is no need to. The bottom of the box needs a 2 to 4" layer of wood shavings (preferably non-aromatic such as cypress or ash) before it's ready for occupancy.

Mount the box as high as your ladder will reach, 10 to 20' is ideal. Boxes should go in open areas, with the box opening not obscured by branches or other cover. Kestrels like to have an open approach vector to reach their boxes, as well as space to maneuver to prevent being captured by opportunistic bird hawks. Poles make ideal mounting substrates, but only use utility poles if you have permission from the company. Trees can be used, but be sure to use only nails or cables to attach boxes to trees. If using nails, put only one above the box and one below - if you use pairs, tree growth could easily split the box. You will have to check the box attachment annually and possibly reset it in order to accommodate tree growth. Sides of buildings, such as barns and sheds, or even on house soffits, can also be good options. In that case, painting the nest box to blend in with the house is acceptable, and the kestrels will still be able to recognize the cavity.

Our experience in Florida has shown that nest boxes do need regular maintenance to keep the boxes clean and safe, and to discourage interlopers (such as starlings, an exotic bird species, and squirrels, who have the ability to build their own nests) from taking over the boxes. If you cannot care for the nest boxes, they will quickly become useless for your target species. Note that native birds, such as screech owls, flycatchers, and bluebirds, cannot legally be harassed. In many states, squirrels are also considered a regulated game species. So check with your local regulations before evicting any non-kestrel residents other than the exotic starling or house sparrow.

You can find more information about caring for a kestrel nest box project at these websites:
Article by Cornell Lab of Ornithology
Kestrels Across America