The kestrel, a small and widely distributed member of the falcon family, is a familiar sight across open landscapes. These raptors, such as the American Kestrel (Falco sparverius) and the Common Kestrel (Falco tinnunculus), occupy an enormous range. Despite their adaptability, their breeding success hinges entirely on finding a very specific location for their young. The availability of suitable nesting sites is a major factor limiting their populations.
The Kestrel’s Obligation to Cavity Nesting
Kestrels are “secondary cavity nesters,” meaning they cannot excavate their own nesting holes. They rely completely on existing cavities created by other forces or animals. These holes are often the abandoned work of primary excavators like woodpecker species (e.g., Northern Flicker) or natural tree hollows formed by decay in dead standing trees, known as snags.
When a kestrel pair selects a suitable cavity, they perform minimal to no actual nest construction. The eggs are typically laid on the bare floor of the cavity, though a shallow depression may be scraped out if loose debris is present. This dependency on finding a ready-made, protected enclosure contrasts sharply with the elaborate stick nests built by many other raptors.
Natural and Wild Nesting Habitats
In natural environments, kestrels seek open habitats like grasslands, scrublands, and agricultural fields. They prefer nest sites relatively high off the ground, typically between 10 and 30 feet above the base. This elevated position provides security from terrestrial predators and allows easy access to hunting grounds.
Tree hollows in isolated or scattered tall trees are a primary natural nesting choice, especially where snags are permitted to remain. Kestrels also utilize natural rock features, readily taking to crevices and small caves found in cliffs and quarries. In arid regions, they may use existing holes in large cacti. The need for a cavity often limits their presence in dense forests, as they favor woodland edges or open areas.
Urban Adaptations and Artificial Structures
Kestrels integrate into human-modified landscapes by substituting natural cavities with man-made structures. They frequently nest in enclosed spaces within abandoned buildings, barns, and crevices on bridges or beneath overpasses. Utility poles and other large, vertical structures provide the height and protection they seek, especially if a small, enclosed space is available. The urban environment offers substitutes for the natural tree hollows often scarce in developed areas.
The most direct human assistance is artificial nest boxes, which kestrels adopt quickly where natural sites are limited. These boxes are typically mounted on poles, trees, or the sides of buildings, ideally 15 to 20 feet above the ground. Proper placement involves facing the box entrance toward the southeast to protect the cavity from prevailing winds while utilizing morning sun exposure. To maximize occupancy, nest boxes should be placed near open fields or pastures, and spaced at least a half-mile apart to respect territorial needs. Adding a few inches of wood shavings or chips provides the necessary substrate for the eggs, and vigilance is required to prevent introduced species, such as the European Starling, from taking over the cavity.