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Door to Nature: Kestrels Need Nest Boxes, Too

The American kestrel is one of our nesting species and will migrate to the south, but in milder winters a few may be seen throughout the cold months along roadsides, especially in southern Door County. This month is a good time to build nest boxes for these falcons of the open countryside.

So much emphasis has been directed to constructing birdhouses for the smaller species, such as eastern bluebirds, that the larger birds, including flickers, kestrels and screech owls end up with few suitable places to raise their young.

In case you live near the edge of town or in an agricultural area having scattered woodlots, trees, shelterbelts, pastures and hayfields, your chances are very good of attracting kestrels to a properly built and erected nest box. We seldom missed a year without a pair of these little falcons taking up residence in a simple nest box fastened along the western edge of our field about 25 feet from the road.

The smallest and most social of the falcons native to North America, the American kestrel, unfortunately had the name of sparrow hawk for too many years. It is true that they take a small number of sparrows, but by far the bulk of their summer food consists of large insects such as grasshoppers and crickets, along with small mammals such as meadow voles.

The closer your kestrel house can be set near mowed grassy areas or short-clipped ditches, or places where there are overhead wires or fence lines, the better the birds will like it, for the simple reason that they habitually perch and scan the ground below for movement of their prey. They can drop down for the capture in the blink of an eye, and then swoop back up to their lookout where they devour the grasshopper or field mouse.

A kestrel is a falcon. True to form, its wings are long and pointed, its tail is longer and tapers at the tip somewhat, its head is rather large and the bird is an incredibly fast flier for short distances. Streamlined is a perfect description. Their flight is generally choppy and direct, flapping their wings and then sailing, flapping and sailing. It is when they cock their wings and go into their famed power dive that they attain such great speeds. They are also known to hover in place over a field to gain advantage of finding mice or voles that live there.

The other two falcons that are occasionally seen in this region are the merlin and the peregrine falcon.

The claim is made that the American kestrel is the most colorful falcon in North America. Look for its chestnut cap bordered with gray, back and tail a rusty brown, wings slate blue and two vertical black bars and one black spot on each side of the white face and neck. The black and white face pattern is an especially good field mark to look for, while its pointed wings in flight are important to observe for speedy identification.

In flight the long, pointed wings (wingspan of about 21 inches) make the kestrel appear considerably larger than it really is. The bird is only 8 inches long compared to a blue jay, which is 10 inches in length. In fact the tiny adult falcon weighs a mere 4 ounces or so.

We have frequently observed eastern bluebirds and other small nesting birds perched on roadside wires within 50 feet of the kestrels. Never once have we seen a kestrel go after one of the small songbirds. Bear in mind that the bluebirds also like to hunt from overhead perches, much like the kestrels. As a matter of fact the kestrels are not nearly as hard on small songbirds as are feral house cats, the loss of habitat and the house sparrows and starlings that may take over some nest cavities.

You can construct a good kestrel nest box from one piece of lumber that is one-inch thick, 9¼ inches wide (actually ordered at the lumberyard as a 10-inch wide board) and 8 feet long. The back of the box is 22 inches long, the two sides and front are 16 inches and the top is 12 inches and the floor is 7½ inches wide. The longer length of the floor (9½ inches – the width of the board) will run from front to back and be nailed to the insides of the sideboards, the front and the back.

The entrance hole is 3 inches in diameter with the center of the opening being around 11 inches up from the bottom of the front. The top is hinged to the back around 3 inches down from the top of the back. This allows enough room for fastening your box at the top and bottom to wherever it will be placed.

Drill four small drainage holes in the bottom and two near the top of each side. A layer of two or three inches of coarse sawdust or fine wood chips should be placed in the bottom of the box. Ideally the nest box should be placed 10 to 20 feet above the ground in a sunny open area not shaded by trees, with the entrance hole facing south, north or east. A nail pounded into the side of the top of the box near the front, and another nail placed in the upper side right below the top nail, will allow you to easily wire the top shut.

Putting a hinge to open the top will allow for easy cleaning and periodical checking during the summer.

Don’t settle for one nest box; build several. The kestrels will be happy and will work at controlling any overabundance of rodents and insects in your area.