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Establishing a Nest Box Program for American Kestrels Along an Interstate Highway

The American Kestrel: North America's Smallest Falcon

Range and Habitat:
American Kestrels live in North, Central and South America from the tree line boundary in Alaska and Canada south to Tierra del Fuego. Kestrels prefer open country, and will inhabit unforested mountainsides up to 1300 feet, grasslands, savannas, deserts, farmlands, and even suburban and urban environments.

Those in the northern parts of the breeding range migrate, while other populations are less migratory. Populations south of approximately 35N (same latitude as Memphis,Tenn.) are, for the most part, permanent residents.
Kestrel movements are not well understood, but information from the recovery of banded birds indicates the northernmost kestrels winter the farthest south (Central America to Panama). Iowa's kestrel population probably contains a mixture of birds that nest in Iowa but winter to the south, birds that winter in Iowa but nest farther north, and those that are year-round residents.

Food Habits:
American Kestrels are generalist predators, feeding on large insects such as grasshoppers, small mammals such as voles, birds of sparrow size, and in some places, reptiles and amphibians.

American Kestrels are monogamous. Pairing begins approximately four weeks prior to egg laying. The male establishes a nesting territory and is joined later by the female, who may move among several territorial males before choosing a mate. The male, or sometimes the female, will try to attract a potential mate's attention by exhibiting a series of power dives from high above the territory. Pairs form and courtship feeding, where the male presents food to the female, becomes frequent. Copulation may precede egg laying by several weeks and occurs with diminishing frequency as egg laying approaches.

Nest Site Selection:
Both sexes have been observed searching for suitable nest sites. American Kestrels are almost exclusively cavity nesters and will use a natural hole in a tree, a woodpecker's hole, a nest box, a cavity in a bank or cliff, or an enclosed space in a building. On rare occasions, kestrels may use an old stick nest of another bird, especially the enclosed nests of magpies.

Eggs are white to reddish-brown, usually with reddish-brown spots. Generally, four to five eggs are laid at one- to two-day intervals.

Incubation generally begins with the second to the last egg laid, and lasts 29 to 30 days. The female does most of the incubation, with the male providing her with food. He occasionally assists with incubation.

Nestling Period:
Kestrel young are tended by both parents. The female broods and feeds the new nestlings, and the male brings all the food. The nestlings are downy white at first, but become well feathered by 20 days of age. The young develop rapidly, leaving the nest 28 to 30 days after hatching.

Post-fledgling Period:
After nest departure, the young are dependent on their parents for food for two to three weeks.

The ideas presented here focus on providing kestrel nesting sites along interstate highways; they are applicable to any highways with grassy rights-of-way and road signs supported by steel posts.

The first step: Obtain permission from your local transportation authority to establish and monitor a nest box route.

Erecting Nest Boxes and Working Along the Interstate:

Nest Boxes
Kestrel nest boxes can either be purchased or built from these plans.

Safety Equipment
Abide by the guidelines set forth by your transportation authority. Use extreme caution while working along the interstate. It is advisable to have a yellow caution light on top of your vehicle and to wear a blaze orange vest and a hard hat.

Placement of Nest Boxes
Attach the box to the sign-post 10 to 30 feet above ground. Space the boxes, on average, one mile from each other and no closer together than one-half mile.

Box use by kestrels will most likely be highest in open areas where natural cavities are lacking. If a box has been in place for three or four years and has not been used, it is advisable to choose a new site.

If a wetland is adjacent to the highway, using somewhat larger
Wood Duck nest boxes will provide nesting opportunities for these birds as well as kestrels. Kestrels will use the larger Wood Duck nest box, but kestrel nest boxes are too small for Wood Ducks.

Attachment of Nest Boxes
Metal banding material is used to secure the nest box to the steel sign-post. Use "C"-clamps to hold the box in place while working. Bands are applied with a tool that is normally used for strapping steel bands around freight. This steel binder is expensive, but is available for rent at many of the outlets that rent tools. One strap is wrapped around the sign-post and board extending above the box, and a second strap is wrapped below in the same manner (see photo). A third strap may be wrapped around the entire box and post and will help hold the box in place in high winds. Stainless steel banding is more expensive than galvanized steel but will not require replacement. In Iowa, galvanized steel banding rusts and breaks in about six years.

Checking and Maintaining Nest Boxes:
Nest boxes should be visited at least three or four times each year. The first visit should occur before the kestrels begin territory establishment. The date of the first visit will, of course, vary from one region to another. Because kestrels establish their territories in mid-March in Central Iowa, in this area the first box check is made in late February or early March. At this time, nest boxes are cleaned and repaired, and three to four inches of wood chips, wood shavings, or straw are added to the bottom of each box.

To monitor nest box use by kestrels, boxes should be visited two to three times during the nesting season. Several additional visits will be necessary to obtain accurate data to evaluate nesting success. To determine whether the young kestrels have successfully left a nest box, one visit should occur within five days of their expected nest departure. Because kestrels are especially sensitive to disturbance during the first two weeks of their 30-day incubation period, avoid visiting the boxes at this time (last two weeks of April in Central Iowa). The last visit should be made in late summer after nesting to remove old nesting material and to do repairs.

European Starlings often nest in kestrel nest boxes. Starlings replace or cover wood chips with grass and other material and lay five, six or seven pale blue eggs. If starlings are found nesting, remove the nest and replace it with a new layer of wood chips. Sometimes kestrels will evict starlings from nest boxes. If this happens, the kestrels will use the starling's nesting material.

Records kept for each box on each visit will help to evaluate the sucess of individual nest boxes, the nesting sucess of your kestrel population, and ultimately, the sucess of your nest box program.

Iowa's Nest Box Program
In 1983 Ron Andrews of the Iowa Department of Natural Resources originated the interstate nest box program for American Kestrels. Working in cooperation with the Iowa Department of Transportation, nest boxes were attached to the backs of information signs along the interstate rights-of-way. Twenty nest boxes were placed on signs along I-35 in Northern Iowa that first year as an Eagle Scout project, and eight were used by kestrels. Nest boxes now occur nearly every mile of I-35 from Missouri to Minnesota. This corridor represents the nation's first statewide kestrel trail along an interstate system. These efforts have been coordinated by the Iowa Department of Natural Resources Nongame Wildlife Program and implemented at the local level by state nongame personnel, county conservation personnel, and a host of volunteers. Hundreds of nest boxes have been attached to highway signs elsewhere in Iowa. Many other states, including Rhode Island, Nebraska, and Idaho, have adopted the kestrel box program.

American Kestrels require open terrain for hunting, and the grassy rights-of-way are ideal for this purpose. While driving the interstate, it is not uncommon to see a kestrel hovering above a right-of-way or perched on a power line searching for prey. The nest boxes are predator-proof because raccoons and other predators are unable to climb the steel posts which support the signs.

In Iowa nest box use by kestrels averages 50%, and young are sucessfully raised in about 70% of these boxes. European Starlings occupy most of the boxes not used by kestrels. With an average of three young kestrels raised in each successful kestrel nest box, each year the Iowa program yields about 105 young for every 100 nest boxes in place.

Dan Varland studied the behavior and survival of young kestrels leaving their nest boxes along I-35 for his doctoral research in Animal Ecology at Iowa State University. Dan followed the young by attaching radio-transmitters to them just before they left their nests. Dan attached transmitters to a total of 61 birds during each of three summers, 1988 - 1990. He found that the young left the interstate right-of-way soon after they could fly and went to nearby areas to hunt and for cover. Only 2 of the 16 young kestrels found dead were killed as a result of collisions with vehicles along the interstate, indicating that traffic was not a major source of mortality.

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