Nest box planning and construction:

Barn Owls do not construct their own nests; rather, they make use of existing nest sites such as attics, burrows, caves, or deserted buildings. However, the expansion of constructed areas, human development, reduction in open landscapes, and increase in intensive agriculture have drastically reduced available nest sites for Barn Owls. This shortage of appropriate nesting sites acts as a limiting factor for Barn Owl reproduction. Nest box construction and installation in agricultural areas address this issue by providing the necessary nesting sites, thus enabling Barn Owls to reproduce and populations to grow. These nest boxes are intended to replace natural nesting sites and must be large and spacious. It is important to bear in mind that the average Barn Owl clutch size (in the Israeli project) ranges between 4-7 eggs, and when food is plentiful, much larger clutches are possible (up to 13 eggs). Hatchlings spend roughly 60 days in the nest box and stay in its vicinity for an additional month. Since chicks approaching fledging are roughly adult-sized, they require a spacious nest, which means a large nest box. Furthermore, if a nest box is to be installed on a pole, its size must be adapted to the pole’s carrying capacity.

Suggested nest box models and measurements:

Suggested nest box measurements: there are two recommended nest box models, each with its pros and cons (for further inquiries, contact your regional coordinator). The Shauli model has a length of 75-100 cm, width of 50-60 cm, and height of 50-60 cm (see nest box illustration). The English model has a width of 50-60 cm, a depth of 40-50 cm, and a height of 60-70 cm (see nest box illustration). For ventilation purposes, ensure there is a space between the nest box walls and roof, or drill holes in the upper parts of the box. Nesting seasons may start with a cycle between February and July and an additional cycle lasting until September. During very hot days, proper ventilation is crucial to prevent chick death from heat and dehydration.

Entrance: ~15*15 cm.

Landing pad: Must extend roughly 20*25 cm below the entrance. The pad enables landing prior to entry and also serves as a lookout. It is also important for older chicks, who wait outside the box for their parents to return with a catch.

Side door: An upward or sideways opening side door must be fitted to each nest box. This door is used for monitoring and research purposes, as well as for cleaning at the end of each nesting season.

Important issues during construction:

It is recommended to construct nest boxes from 12-18 mm thick solid wood or plywood. The nest box must remain dry throughout the year, as water leakage into the nest cavity and the absence of proper drainage will affect nesting, prevent brooding, and kill chicks. During construction, always ensure you seal off any weak points that are liable to water entry and apply a coat of flax oil on the nest box before painting. For emergency cases of water entry, drill four 10mm wide holes in the floor of each nest box.

We recommend applying at least two coats of white paint to the entire nest box. After painting, each nest box must be clearly marked with a number or letter that will be visible from a distance. The marking must be clear, weather-resistant, and will identify each nest box. Marking your nest boxes will make maintenance and monitoring easier and more efficient.

Placing your nest box in the field:

In standard areas where landscape coverage is composed of mixed open landscape and forests or plantations, start with a nest box density of one per 100 acres. As your project advances, you may either add or remove nest boxes according to results in the field.

Nest boxes must be placed in an accessible location. When placed in agricultural areas, nest boxes must be positioned so that they do not disrupt field work, such as next to faucets.

Make sure the nest box opening and its surroundings are clear of foliage or other obstacles to ensure a comfortable approach to the landing pad. The nest box opening should preferably face south to reduce direct sunlight entry to the nesting chamber. Locations that are shaded at noon (even partially) are preferable.

Nest boxes can be placed on existing structures like rooftops or existing poles. When placed on top of a pole (2″ diameter), the pole must be anchored 80-100 cm deep into the ground and properly stabilized. The recommended height is 2.5 m above the ground. Taller, and access for farmers or operators becomes difficult; shorter, and access becomes easy for curious bystanders who may possibly disturb the nest.

Timing of nest box introduction to the field:

Nest boxes should be installed as soon as possible upon deciding to join the project and completing construction. Barn Owl’s settlement of a new nest box may take months or even years. In Barn Owl rich environments where nest site availability is limited, a newly located nest box placed at the right time might be occupied immediately. In Barn Owl’s poor environments, it may take years for a well-established population to build up. For example, 15 nest boxes placed in the fields of Kibbutz Alumim in the western Negev in November 1998 were only used for the first time in March of 2002, the fourth nesting season since the boxes were placed!

Barn Owls prefer to be well acquainted with nest boxes in their area, which makes new nest box installations during or after nesting important. Newly fledged fledglings explore the area around the nest and become familiar with new nest boxes, while adults may “adopt” these boxes as feeding or resting sites, especially if they are placed in a cool, well-shaded environment.

Care and maintenance-annual schedule:

Nest box cleaning: Nest boxes must be cleaned once nesting is finished and fledglings have abandoned the area (around August for a single cycle). As the season progresses, a thick layer of prey remains, pellets, and droppings accumulate at the bottom of the nest box, reducing the nesting cavity volume, and this must be removed. Those involved in research can use pellets and other remains for their purposes, while others should simply empty out the nest box. Cleaning also reduces the chances of parasite transmission from one season to the next. However, cleaning should not be overdone; a thin layer of “Barn Owl dust” will help returning Barn Owls identify the nest box upon their return.

Maintenance: Cleaning is a good opportunity to make an inventory list of needed repairs and renovations for the next season. Fallen hooks, torn hinges, or misplaced doors are examples of common wear and tear. Paint must also be reapplied every few years when bare wood begins to show through the older layers. Sometime in mid-Autumn, preferably in November, an additional inspection should be made to identify and fix any occurring problems ahead of the coming nesting season.

Nest boxes should not be approached during winter, but occasional observations are necessary. If familiar people are working around the nest boxes, inform them about their existence and purpose and ask for occasional reports of malfunctions and Barn Owl activity. Nest box openings must be checked regularly to ensure entry openings are clear and open, and side openings are well shut. Spring brings nest site competition, and some species may try to hijack “our” nest boxes. Any intruding birds (pigeons, mynas, jackdaws, sparrows) must be removed to allow Barn Owls to nest. Falcons may inhabit some of the nest boxes, but these are not considered intruders because they also feed on rodents.

Wasps may occasionally settle into a nest box, especially in irrigated fields. One nest box-loving species is the European paper wasp (Polistes dominula), which must be exterminated and kept away from nest boxes persistently. These are our duties, and from here on, nature takes its course.

We must avoid any intrusion on nest boxes during brooding (early March to late April). Look out for a second nesting cycle and be careful not to intrude on it as well. Any interference during this period may lead to nest abandonment. Nest boxes should not be approached until all eggs have hatched. At this stage, early hatchers have already formed a strong relationship with the mother, and she will return to the nest despite the intrusion. Of course, any unnecessary intrusion should preferably be postponed as long as possible.

Observation, hunting, and resting posts:

Elevated perching posts aid Barn Owls in their hunting and serve as resting and feeding posts. These perching posts also encourage day raptors to approach the field for rest and rodent hunting, especially during migration in Spring and Autumn. Perching posts should be placed at a density of one per 20 acres, positioned between nest boxes, particularly in open areas devoid of natural perches. They should be T-shaped and located 3 meters above the ground. The perching bar should be at least 30 mm wide (like a shower handle) for birds to feel stable, and the wider the better.

Processed from: Shauli Aviel, Yoav Motro, Dr. Gila Kahila Bar-Gal, Dr. Yossi Leshem; Barn Owl as biological rodent pest controllers, farmer’s background material. 2003.