Providing suitable nesting sites for birds of prey such as kestrels and owls is a rewarding way to support local wildlife and observe fascinating natural behaviors up close. Nest boxes, also known as bird houses or nesting boxes, are artificial structures designed to mimic the natural cavities these birds seek for breeding and shelter. This article offers a comprehensive woodworking plan tailored specifically for kestrels and small owl species, along with detailed guidance on their taxonomy, habits, and conservation. Understanding these birds’ needs and characteristics ensures that nest boxes are both safe and effective, encouraging successful breeding and helping maintain healthy populations.
Scientific Classification
The term “kestrel” typically refers to small falcons within the genus Falco, notably the common kestrel (Falco tinnunculus) found across Europe, Asia, and Africa, and the American kestrel (Falco sparverius) native to the Americas. These birds belong to the family Falconidae, characterized by their sharp talons, hooked beaks, and exceptional hunting abilities. Kestrels are among the smaller falcons, known for their hovering flight while hunting.
Owls suitable for cavity nesting boxes include the eastern screech owl (Megascops asio) and western screech owl (Megascops kennicottii), both members of the family Strigidae. These small owls are widespread across North America and are adapted to forest and suburban environments. Another species sometimes attracted to nest boxes is Barrow’s goldeneye (Bucephala islandica), a diving duck that nests in tree cavities, though specialized nest boxes are needed for this species. Understanding the specific taxonomy of these birds helps in designing nest boxes that cater to their particular size and behavior.
Geographic Range & Distribution
Kestrels have a broad geographic distribution. The common kestrel inhabits much of Europe, North Africa, and Asia, thriving in open habitats such as farmland, grassland, and urban areas. The American kestrel, the smallest falcon in North America, ranges from Alaska and Canada down to Central America, favoring open fields, deserts, and even city parks. Their adaptability to varied environments makes them common sights across their range.
The eastern screech owl is widespread in the eastern United States and parts of Canada, occupying deciduous woodlands, suburban areas, and parks. Its western counterpart, the western screech owl, inhabits a similar niche across the western U.S. and into Mexico, preferring wooded areas near water sources. Barrow’s goldeneye, meanwhile, breeds in the boreal forests and mountainous regions of western North America and parts of Alaska. They require nest cavities near lakes or rivers, where they forage for aquatic invertebrates and fish.
Physical Description
Kestrels are small falcons, with the American kestrel measuring approximately 22–31 cm (8.7–12.2 inches) in length and sporting a wingspan of 51–61 cm (20–24 inches). They weigh between 80 and 165 grams (2.8–5.8 ounces). Males typically have blue-gray wings with spotted reddish backs, while females are more uniformly brown. Their distinctive facial markings include a mustache stripe and dark vertical streaks on the face. These features aid in identification during birdwatching.
Screech owls are compact and stocky, measuring about 16–25 cm (6.3–9.8 inches) in length with wingspans of 42–58 cm (16.5–22.8 inches). They typically weigh between 120 and 250 grams (4.2–8.8 ounces). Their plumage varies between gray and reddish-brown morphs, providing excellent camouflage against tree bark. Both kestrels and screech owls have large eyes adapted for low-light hunting, but their hunting styles differ significantly.
Behavior & Diet
Kestrels are diurnal hunters that rely on keen eyesight to spot prey from perches or while hovering in the air. Their diet mainly consists of small mammals such as voles and mice, insects including grasshoppers and beetles, and occasionally small birds. They are known for their ability to hover in place, beating their wings rapidly while scanning the ground. This hunting method is unique among falcons and allows kestrels to exploit open habitats effectively.
Screech owls are nocturnal predators, hunting primarily at dawn, dusk, and nighttime. Their diet includes a wide variety of prey such as insects, small mammals, birds, and occasionally amphibians and reptiles. These owls use their acute hearing and silent flight to ambush prey in dense vegetation. Their territorial calls and ability to mimic other species also play a role in communication and territory defense.
Breeding & Reproduction
Both kestrels and screech owls are cavity nesters, relying on natural tree holes or abandoned woodpecker nests, which is why nest boxes are essential in areas where natural cavities are scarce. The typical kestrel nest box should be roughly 15 inches tall, with an internal floor dimension of 8 by 8 inches, providing enough space for the female to lay 4 to 5 eggs and raise the chicks. The entrance hole should be about 3 inches in diameter and located approximately 12 inches above the floor to protect from predators and weather. Notably, kestrels do not require a perch outside the entrance, as this can aid predators. According to eBird, this species is well documented.
Screech owl nest boxes share similar size requirements but may be slightly smaller given the owl’s compact size. These boxes should also have a 3-inch diameter entrance hole, positioned to minimize exposure to harsh weather and predators. Ventilation holes are recommended, typically placed under the roof and in the floor to maintain airflow and reduce moisture buildup, though opinions vary among experts on their necessity. A hinged roof secured with corrosion-resistant hardware allows for easy cleaning and monitoring after breeding season. According to BirdLife International, this species is well documented.
Appropriate placement is critical: mounting nest boxes on poles or in trees at heights between 8 and 20 feet offers protection and reduces disturbance. Adding a predator guard, such as an inverted metal cone below the box, can deter raccoons, snakes, and other potential threats. After the breeding season, removing, sanitizing, and repairing nest boxes ensures they remain safe and attractive for the next cycle.
Conservation Status
Both kestrels and screech owls are currently listed as Least Concern by the International Union for Conservation of Nature (IUCN), reflecting stable population trends across much of their ranges. However, habitat loss, pesticide use, and competition for nesting sites can pose localized threats. Urban expansion reduces available natural cavities, making artificial nest boxes an essential conservation tool.
Barrow’s goldeneye, while also listed as Least Concern, faces challenges from logging and changes to aquatic ecosystems that affect their breeding habitats. Conservation efforts focused on preserving mature forests and riparian zones benefit these cavity-nesting species. Installing nest boxes in appropriate environments helps maintain breeding opportunities amid changing landscapes.
Interesting Facts
Kestrels are one of the few birds of prey capable of hovering steadily in place for extended periods, a hunting technique that earned them the nickname “windhover” in some regions. Their ability to see ultraviolet light allows them to detect the urine trails of small mammals, improving hunting success. Eastern and western screech owls are known for their distinctive trilling calls and remarkable ability to camouflage themselves against tree bark, making them elusive to predators and observers alike.
Another fascinating aspect is the communal use of nest boxes by multiple bird species. While kestrels and screech owls prefer their own boxes, other cavity-nesting birds such as bluebirds, chickadees, and woodpeckers may also take advantage of these structures, promoting biodiversity in the area. Installing nest boxes thoughtfully can encourage a variety of species to breed safely, offering unparalleled opportunities for wildlife enthusiasts and photographers.
Barrow’s goldeneye is unusual among ducks for its preference to nest in tree cavities rather than ground nests, which aids in avoiding predators. They often take over old woodpecker holes, and nest boxes designed for them feature larger entrance holes and more spacious interiors to accommodate their size and breeding needs.
Conclusion
Building and installing nest boxes for kestrels and owls is a meaningful way to engage with and support local wildlife. Understanding the specific requirements of each species—from dimensions and materials to placement and maintenance—ensures these artificial homes provide safe, comfortable nesting sites that mimic natural conditions. By offering shelter to these captivating birds of prey, nature enthusiasts contribute to their conservation while enjoying the unique opportunity to observe their secretive breeding behaviors.
Carefully crafted nest boxes made from durable, untreated red cedar or exterior-grade plywood provide longevity and protection against the elements. Features such as sloped, overhanging roofs, ventilation openings, and predator guards enhance the suitability of the boxes. Removing and sanitizing boxes yearly reduces disease risk, promoting healthy populations. Whether in rural landscapes, suburban gardens, or forest edges, thoughtfully designed nest boxes can support kestrels, screech owls, and other cavity nesters, enriching biodiversity and deepening our connection with the natural world.
