The Barn Owl (Tyto alba) is one of the most widespread land birds globally, found on every continent except Antarctica. This species, recognizable by its pale face and heart shape, does not build an open stick nest like many other birds. Instead, the Barn Owl is a secondary cavity nester, meaning it seeks out dark, sheltered openings in which to lay its eggs and raise its young. The preference for these enclosed spaces offers protection from the elements and predators, making the availability of suitable cavities a factor that often limits the owl’s population in a given area.
Primary Nest Locations
Barn Owls select their nesting sites based on the availability of existing sheltered cavities, which can be broadly divided into natural features and structures created by humans. In natural environments, the owls frequently use large, hollow sections of old-growth trees, such as sycamore, maple, and oak. They also utilize natural recesses in rocky landscapes, including cliff crevices, caves, and sheltered banks along rivers or ravines, which offer the necessary concealment and quiet.
Man-made structures have provided an important alternative for nesting, leading to the owl’s common name. The interior of old, seldom-used buildings like barns, silos, and abandoned houses are highly sought after because they offer large, dry, and dark spaces. Nesting pairs will often enter through broken windows or open doors to find a ledge or flat surface on a high beam or in a loft. Additionally, the owls will colonize the bell towers of churches, water towers, and even highway bridges, especially in areas where natural tree cavities are scarce.
The Characteristics of a Barn Owl Nest
The term “nest” is somewhat misleading for the Barn Owl, as the birds are poor nest builders and do not construct a woven cup of materials. Instead, they rely on the existing flat surface within the chosen cavity, whether it is a wooden floor, a concrete ledge, or the bottom of a tree hollow. The female often simply lays her eggs directly onto this surface, or she may create a shallow depression by scratching at the substrate.
Over time, the nest area develops a unique composition. The primary material that accumulates is a layer of compacted, regurgitated pellets, also known as castings, which are the indigestible fur and bone remains of their prey. As these pellets break down, they form a debris layer that provides a degree of insulation and a soft surface for the eggs. The presence of a white, chalky substance, often called “whitewash,” covers the walls and surrounding area, consisting of accumulated droppings, further marking the location as an active nesting site.
The Barn Owl Breeding Cycle
The timing of the Barn Owl’s breeding cycle is highly flexible and primarily driven by the abundance of food. In temperate regions, courtship often begins in late winter or early spring, with the male bringing food to the female to prepare her for breeding condition. The female then lays a clutch of between four and seven eggs on average, with a new egg laid every two or three days.
Incubation begins immediately after the first egg is laid, rather than waiting for the full clutch, resulting in asynchronous hatching. This staggered process means that the owlets hatch a few days apart, leading to a visible difference in age and size among the siblings. The incubation period lasts approximately 30 to 34 days. The young remain in the nest for an extended fledging period, often leaving the cavity around nine to ten weeks after hatching. When prey is exceptionally plentiful, a pair may attempt a second clutch in the same season.
Encouraging Barn Owl Nesting
Humans can significantly aid local Barn Owl populations, which are often limited by a lack of suitable nesting cavities, by installing artificial nest boxes. These boxes provide a safe, dry, and protected space that mimics the natural cavities the owls seek.
Indoor Nest Boxes
For an indoor box placed in a quiet barn or shed, a minimum floor space of 0.2 to 0.4 square meters is generally recommended to comfortably house a brood. The depth of the box is important, with the entrance hole needing to be at least 450 millimeters above the box floor to prevent young owlets from prematurely falling out.
Outdoor Nest Boxes
For outdoor boxes mounted on poles or trees, a weather-resistant material like treated plywood is used. The box should be situated at least 12 to 15 feet high in open country overlooking hunting habitat. The entrance should face away from prevailing winds and have a clear flight path. Ensure the site is quiet and undisturbed, especially during the nesting period between late winter and late summer.