Species History and Nest Box Info

Historical Significance

The bird is often referred to as the sparrow hawk because of its small size. Its scientific name, Falco sparverius, holds the Latin meaning, "falcon of the sparrows."

Population Decline

The American Kestrel is the continent’s most common and widespread falcon, but populations declined by an estimated 1.39% per year between 1966 and 2017, according to the North American Breeding Bird Survey. That annual trend corresponds to a 51% cumulative decline over the full period. Partners in Flight estimates the global breeding population at 9.2 million. The species rates a 10 out of 20 on the Continental Concern Score, indicating a species of relatively low conservation concern. Nevertheless, if current trends continue, American Kestrels will lose another 50% of their population by 2075. Current declines stem from continued clearing of land and felling of the standing dead trees these birds depend on for their nest sites. A growing human population contributed to the loss of nesting habitat as well, as fencerows and tree-lined field borders were removed to provide crop fields and make way for expanding urbanization. The American Kestrel is also losing prey sources and nesting cavities to so-called “clean” farming practices, which remove hedgerows, trees, and brush. An additional threat is exposure to pesticides and other pollutants, which can reduce clutch sizes and hatching success. For kestrels in North America, a larger problem with pesticides is that they destroy the insects, spiders, and other prey on which the birds depend. A management practice that has helped to improve the kestrel’s status is the placement of artificial nesting structures on road signs along highways and other areas of suitable kestrel habitat.

Now What? - Nest Boxes

Nest Box Design

Nest boxes should be constructed of a weather-resistant wood such as cedar. The wood can be painted or stained but only on the outside surface. The entrance hole should be 3 inches in diameter. Numerous nest box designs have been used with success; including Audobon's or Hawk Mountain. A good method of assisting fledglings in their climb from the nest to the entrance hole is to roughen up the inside wood surface under the hole with a chisel. It is recommended that the outside surface below the entrance hole be roughened as well. The bottom of the box should be lined with 2 to 3 inches of wood chips or shavings, straw, or pine straw. The lid or one side of the box should be removable or on a hinge to facilitate monitoring and cleaning. Three or four-inch drain holes should be drilled into the box bottom. Recessing the box floor _-inch into the bottom edge of the walls will help protect the floor from weather rot. Ventilation and shade requirements are met by overhanging roofs and construction designs described in Fig. 1. All kestrel boxes affixed to poles should be fitted with a galvanized sheet metal predator guard. The predator guard should be placed on the pole 6 to 12 inches below the bottom of the box. Also, to help deter predation, an even coating of non-drying crankcase grease or carnauba wax can be applied to the pole from the ground to six inches below the box.

Placement

Kestrel nest boxes should be placed on a tree, post, or the side or a barn or outbuilding with the entrance hole 15 to 20 feet above the ground. Boxes placed on posts should be equipped with a predator guard. The box entrance should face southeast to avoid direct winds and to take advantage of the sun's rays. Open fields, pastures, hedgerows, and highway and power line rights-of-way comprised of or surrounded by at least one acre of space within 20 yards of a tree with dead limbs, a utility pole, or other perch make up the best habitat in which to place nest boxes. These habitat types in close proximity to creeks and wet areas have proven to be very productive for kestrels as well. Place boxes well away from buildings and other human habitations that may harbor starling populations. Also, placing boxes more than 50 yards from woodland edges will help reduce competition for boxes with squirrels. Open areas will provide food for hunting and adjacent trees, utility poles, and fence posts are used as plucking perches by the male kestrel to dismember prey before the female feeds it to the young. Perches are also used for preening, courting, and by fledglings when learning to fly. Individual nesting pairs require an adequate territory in which to nest and forage. Therefore, nest boxes should be placed at least one-half mile from one another. Boxes placed near or along roadsides should be placed with the entrance hole facing away from the road. In agricultural areas, it is important that nest boxes be located a distance away from fields that are heavily treated with pesticides since the birds feed primarily on insects. Overall, one should attempt to accommodate the bird’s natural nesting instincts and requirements while still allowing for routine monitoring during the nesting season. If predators such as raccoons or snakes discover an occupied nest box, they likely will continue to return for eggs or nestlings in the future. If such predation becomes a problem, relocating troubled nest boxes after a few seasons may be beneficial.

Exotic Species Control

Exotic species, specifically the European starling, compete with American kestrels for nesting cavities. Simple steps can be taken, however, to reduce nest box use by starlings. If starlings are found to be nesting in a box, remove and dispose of the nest and its contents. The actual trapping and elimination of the adult bird in the box is more effective than simply removing the nest. Trapping with inside-the-box traps or bait-type traps such as those made by Trio and Hav-a-hart is recommended. If relocation of trapped birds is preferred over disposal, the birds should be taken a distance of at least three miles from the trapping area and released in similar habitat. However, the significant drawback of this management technique is that it simply may move the problem birds from one location to another. If you are uncomfortable with removing the birds or nests, another option is to vigorously shake the eggs, or addle them, for 60 seconds and leave them in the nest so that the female will continue to expend reproductive energy without hatching success. This also prevents the starling from attempting to take over another nest box. Other native cavity-nesting birds, such as eastern screech owls and eastern bluebirds may use and are welcomed in nest boxes. Because they are federally protected, it is illegal to destroy them, their nests, or their eggs. Therefore, nest monitors must be certain of the bird species nesting in a box before control measures are implemented. Two aids, Guide to Nests, Eggs, and Nestlings of North American Birds, and Birds’ Nests (in the Peterson Field Guide Series) are recommended (complete citations included in the reference section). Note: Box placement is the best means of controlling exotic species. Careful box placement will also reduce competition from squirrels. Placing boxes a good distance from buildings and human habitation and orienting them with a southern exposure will help prevent starlings from using kestrel boxes. Placing boxes in open grassy areas away from woodland edges will help to reduce over-use of boxes by non-target native bird species and squirrels.

Nest Box Monitoring

Because the kestrel has such an expansive range throughout North America, the time period in which nesting activity begins in various regions differs. In southern, western, and other warm regions in which the kestrel is a year-round resident, eggs are typically laid by the first week of March. Colder, more northern reaches typically see eggs laid in mid to late April. The establishment of nesting territories generally begins three to four weeks prior to egg laying; therefore, the first visit to nest boxes should occur before this date. First visits should clear nest boxes completely of all materials, as well as make any necessary repairs to boxes. Two inches of wood chips or shavings should be placed in boxes at this time. Observation of nest boxes from a distance of 50 to 75 yards is necessary to determine if nesting activity is taking place. Observations should be made between mid-morning and late afternoon, three to four times a week, from mid-March through late June depending on the region. Activity common to nesting kestrels consists of frequent entering and exiting of nest boxes by both the male and female bird. Visits to nest boxes (to check on egg status) should occur 10 to 14 days after the male kestrel is seen bringing food into the nest box. Opening boxes before this time may prevent the female from laying her entire clutch of eggs or discourage her from using the box. Visits should document the eggs, being careful not to unnecessarily disturb the nest. Third visits should be made about two weeks prior to the expected fledging date of the nestlings. Approximate fledging dates can be determined by adding 46-50 days to the estimated date that the last egg was laid. A count of nestlings in the box should be recorded. Monitors should use extreme caution when opening boxes at this time to prevent nestlings from prematurely exiting the box. Banding of nestlings should occur during the third visit if part of the nest box program. Banding activities should be done in cooperation with a bird expert and licensed bander. The fourth visit should occur one month after the nestlings have fledged to clean nest boxes of all nesting materials. Boxes should remain out during the winter to provide winter cover for kestrels, screech owls, and other resident birds. European starling nests should be removed and disposed of when found to be the sole contents of a box and no sign of kestrel use is apparent.