American Kestrel Nest Box Conservation

March 2023, version 1.0

 

 

A Project of Kestrel Heights
 

Introduction

Thank you for your interest in American Kestrel Nest Box Monitoring Program. This is a project in cooperation with the National Audubon Society. Our efforts to place nest boxes in appropriate breeding habitat and monitor their use will help us to understand the breeding distribution of kestrels in the state and increase the number of nesting options for a species which is experiencing declines throughout its breeding range.

Nest boxes should only be installed if the volunteer intends to monitor and maintain the box throughout the season. An unattended box can be detrimental to kestrels and other native nest box users if non-native species begin using the box. Paper wasps, mice, squirrels, and even snakes may take up residence in an unattended nest

box. For more information on how to handle these situations, see the “Maintaining Nest Boxes” section below.

 

 

Why Monitor American Kestrels?

Hole nesting species have been able to find and use natural cavities in trees and other crevices naturally found in the wild, so why does Iowa need nest boxes for these species? Birds have been getting help from humans for some time – think about all of the bird feeders that are put out in Iowa each year. In addition, some bird species are losing nesting habitat. Natural nesting cavities can be found in areas with lots of standing deadwood, but sometimes this standing deadwood is removed for various reasons or there are no natural cavities suitable for nesting present in an area. Building nest boxes and placing them out in your gardens or other areas can make a difference for species where adequate nesting locations are limited. In addition, there is great

 

value in monitoring how well birds do at raising a brood of chicks, since that influences the number of individuals entering the breeding population in the future.

American Kestrels are currently experiencing widespread declines. Declining kestrel numbers in Iowa have been attributed to a potential increase in competition for suitable nesting sites, loss of grassland habitat, pesticide use, and predation.

Identifying the issues leading to declines in American Kestrels will require a better understanding of the species’ distribution during the breeding season and monitoring their breeding success at nesting sites. Like many other cavity nesting bird species, American Kestrels will readily nest in properly designed boxes placed in suitable habitat. This quality makes kestrels far easier to observe and monitor during the breeding season. Observing kestrels at nest boxes can provide vital information about the species breeding behaviors and the success of their breeding efforts here in Iowa.

 

Natural History

The American Kestrel, once known as the Sparrow Hawk, is the smallest falcon in North America. This small raptor sports colorful plumage, bold facial markings, and, with its long and pointed wings, is a swift predator. It is mostly associated with open habitats such as grasslands, meadows, powerline right-of-ways, and agricultural landscapes, but will also take up residence in more developed areas if suitable nesting and hunting sites are present.

American Kestrels hunt in open areas with low-growing vegetation and are often observed perched on a treetop, utility wire, or building from which they scan their surroundings for prey. In the absence of a perch, kestrels will hover in place by rapidly beating their wings. From their vantage points, kestrels pounce on prey including small

 

mammals such as mice, voles, and shrews, insects such as grasshoppers, cicadas, beetles, dragonflies, and sometimes small songbirds.

American Kestrels are a cavity nesting species. They do not, however, excavate or modify nesting cavities like woodpeckers, chickadees, or nuthatches. They instead usually rely upon the abandoned nest sites of woodpeckers. They prefer nest sites

ranging from 10’ to 30’ in height that are in or on the border of open areas. Males are responsible for finding these nest sites and must attract a female kestrel with their plumage, dive displays, and quality of their selected nest site.

Copulation is a commonly observed breeding behavior between mated kestrels and can be initiated by either pair member. The transfer of food items (from males to females) is part of pair bonding and is a probable indicator that kestrels breed within the area. Pairs tend to remain bonded throughout life and will nest together year after year. Kestrels will breed with new partners, however, if one of the pair is killed or disappears.

 

American Kestrels in Iowa

 

Although American Kestrels live throughout much of North America year-round, this falcon species may overwinter in Iowa or fly south. In the breeding season, however, they are widely distributed throughout the state.

 

Nest Box Monitoring

For this project, we are asking volunteers to install nest boxes in American Kestrel habitat and to monitor these boxes throughout the breeding season. The breeding season is a sensitive time for nesting birds. Because of this, our efforts are designed to

 

minimize disruption that could lead to stress on these birds. The safety of the volunteers, the nesting adults, and their young is a priority. It is important to adhere to the monitoring protocol described below to best guarantee a successful season for all parties. Lastly, it is important to remember that if your nest box remains unoccupied, this is still important information. If no birds take up residence in a nest box this season, that is okay. We still would like for you to collect data that can be used to inform our effort. Give the birds some time to find your box, but if your box remains unused after many years, it is worth moving the box to a new location.

 

Where to Install Nest Boxes

Kestrel nest boxes should be installed in open areas such as grasslands, meadows, agricultural areas, pastures, old fields, parks, shrublands, and residential areas with adequate open foraging space (minimum of acre). Sites with adjacent perches such as snags, isolated trees, posts, utility poles, and other scattered vantage points are especially suitable. Boxes should be placed, when possible, at least 50 feet from wooded areas, however close to perch tree. Sites with extensive tree cover, limited open space for foraging, and near loud roadways should not be used.

Nest boxes should be installed between 8’ and 30’ in height (12’-20’ is our preferred height) on the side of a post or a tree in a field could also suffice. This means you will more than likely need to use a ladder to access the box during monitoring and maintenance. Beware of electricity from overhead power lines, particularly if carrying or placing a ladder, and keep nest boxes at least 50 feet away from any power lines. Ensure your ladder is secure before you climb.

The box should be installed with its opening facing roughly southeast, making sure there is some shade on the box during the hottest part of the day so that the chicks won’t overheat with full sun on the nest box. While some cover (such as tree branches) is acceptable, the box should not be obscured, should be easily viewable from 30’ away, and birds should have a clear flight path to the box. Each kestrel box should be installed a minimum of 0.5 miles apart.

Predators should be considered when picking a location for the nest box. It may be impossible to avoid all potential predators, but pay particular attention if the area has outdoor cats and pick a location for the box where cats cannot climb and access the nest box. If predators are a big problem in your area, consider adding a predator guard to keep them from reaching the box (http://nestboxbuilder.com/nestbox-predator- controls.html).

There are many methods for attaching nest boxes to trees or buildings, and you will need to use the method that best suits your particular needs. You can drill holes into a short piece of wood (wider than the nest box) and tie this tightly to the tree using wire (pad the wire to help protect the tree), then attach the nest box to that short piece of wood.

 

Monitoring Protocol

Here in Iowa, the American Kestrel breeding season runs from approximately 15 May until 15 July. These safe dates indicate the time period where most migrating birds have already reached their breeding grounds. As such, these dates will serve as the start and end date for conducting nest box monitoring. Nest boxes (with coarse wood shavings – not sawdust – in the bottom of the box) should be installed by April 20th, if possible, to best ensure that the box is considered by arriving males.

It is important to remember that nest boxes are not always used immediately after they are put up (we expect less than 50% of boxes will be used in the first year), and we hope that this does not discourage you. Perseverance is essential as it takes time for birds to find a nest box and learn that it can be safe for nesting. If your nest box does not attract a nesting kestrel, it is not a wasted effort. Other species may still use the box for nesting or roosting.

25 May to 22 June: Monitoring should be conducted once per week. During these first four weeks of monitoring ending on 22 June, observations should be limited to viewing the nest box from a distance of approximately 30’ to avoid disrupting the kestrels during the early nesting phase. The time and duration of your visit is up to you and your availability. We ask that you spend at least 15 minutes conducting observations per visit during this period. Note that opening the nest box early in the nest cycle may cause the birds to desert the box, so this is strongly discouraged.

 

Maintaining Nest Boxes

Proper maintenance of a nest boxes is just as important as nest box placement. Nest boxes should be cleaned annually and, when necessary, repaired between seasons. At the end of the season (once all the young have fledged and the nest box is unoccupied), take down the kestrel box. Leaving the box up between seasons will shorten the life of the box and could mean squirrels, wasps, mice, or other species could nest in the box. Take down the box, empty it of any nest materials (wear gloves), and store the nest box in a dry, protected place until the next field season. Do not use any cleaning solutions when cleaning out the box. If there is a build-up of debris stuck inside the box, use warm water and stiff-bristled brush to clean out the box (dry in the sun before storing). If any major repairs are needed, consult the nest box design instructions to complete the repairs yourself so long as you are comfortable doing so. Fresh coarse wood shavings (2-3 inches deep) should be used to line the inside of the box. Sawdust should not be used as it will clog the drainage holes, hold moisture when wet, and could possibly cause drowning of the chicks.

 

A note on competition with non-native bird species: Introduced Old World species such as European Starlings and House Sparrows often compete with native species for nest boxes. The larger diameter openings required for American Kestrel nest boxes make simply excluding these species impossible. These introduced species threaten native wildlife and are therefore not protected by state or federal laws. If Kestrels have already started using the box, they are usually successful in defending their box against these species. If Kestrels have not found the nest box, there are two options if invasive bird species take up residence in the nest box. Option 1: Nest box removal. Once an invasive species moves into the box, it is unlikely that kestrels will use the box that same field season. Therefore, volunteers who are comfortable doing so are welcome to remove nest boxes for the season and dispose of any materials, nests, and eggs associated with an invasive species discovered in an American Kestrel nest boxes.

These contents should be disposed of well away from the nest box. Option 2: Continue your observations. While preventing invasive species from nesting is the ideal solution, some volunteers may not feel comfortable disposing of invasive species nesting materials and eggs. That is okay. If that is the case, you are encouraged to continue your observations. If you observed European Starlings or House Sparrows entering the box, inspect the box as soon as possible to confirm the invasion and either remove the box for the season or continue making observations of the invasive species. If one of these non-native or any other native species takes up residence in your nest box(es), note the species in the comment section on your form. If a native bird species takes up residence in the box, simply make note on your data sheet and continue your observations. Native bird species should not be disrupted regardless of if they are the project’s target species.

 

A note on competition with other wildlife: Occasionally, you may discover that other forms of wildlife have taken up residence in your nest box. These may include mice, squirrels, insects, and snakes. These animals can be removed from the nest box if you are comfortable doing so. Should you decide to remove these animals, proper precautions should be exercised during this type of maintenance. If rodent nests are found within the box, remove the contents with gloved hands. Small paper wasp nests can be manually removed from boxes and destroyed with a gloved hand. Do not use any insecticides to exterminate insects as these products may contain chemicals which can be hazardous to nesting birds using the box. If a particularly large nest of stinging insects is suspected or detected, make note. Large stinging insect nests will likely have to be removed at the end of the season. Unless discovered and removed quickly at the beginning of the season, the presence of any of the animals discussed above will likely mean kestrels do not use the nest box this field season. Any box which is invaded by

these non-bird animals should be relocated to a new location the following field season. Do not risk injury for the sake of nest box maintenance.

 

Nest Box Plans

A good nest box design must be secure from predators, weatherproof, simple and inexpensive to construct, monitor, and maintain, and the target species must accept and use the box to successfully fledge healthy young. A limited number of Kestrel nest boxes are available free to volunteers. If we have run out of our supply of nest boxes, you can get on a waiting list when additional nest boxes are available, or you can build your own using the plans below. See the “Contact” section should you have any questions about the nest box plans. These nest plans were generously shared by The Peregrine Fund. Note that the dimensions given in these plans do not need to be measured to the nearest fraction of an inch - natural nest holes where kestrels nest are variable in size and their openings also differ in size and shape. There is room for experimentation in nest box design, defense against predators, and location. Using wood from scrap piles or even driftwood will help to keep costs down. Do not paint or treat the wood for a nest box with any preservatives. Do not add a perch to the box as they are not needed by kestrels and would provide a foothold for predators. It is often helpful to use a marker to number your nest boxes so that it is easier to keep track of multiple nest boxes.

 

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