There are two basic types of nest boxes for Tawny Owls. The upright design as shown in Fig. 1 is normally strapped or nailed to the side of a vertical tree trunk or major branch. The sloping type as shown in Fig. 2 is designed to be strapped or tied to the underside of a sloping side branch at an angle of approximately 45°. Exact dimensions are not too critical provided that the box is big enough with an entrance hole not less than 200mm square. The upright type box should be fitted with a thick roofing felt top. Both types must have several large drainage holes in the bottom not less than 12mm diameter.
Use pressure treated (tanalised) 18mm planks, or 18mm softwood ply (known in the building trade as CDX). Please avoid using hardwood ply unless it is stamped ‘FSC Approved’. If pressure treated timber is not available, use a brush-on preservative and ensure that all the edges are treated before assembly. Whichever timber treatment you use be sure to follow the manufacturers’ instructions and make sure that the box is completely dry before erection. Assemble the box using galvanised 50mm (2″) nails and/or brass or plated screws. We recommend the use of ratchet straps or polypropylene rope to fix the box to the tree as these cause minimal damage. Nails cause greater damage, but are often the most practical option.
The most common nest site is usually a mature tree in a copse or larger stand of trees. Moist deciduous
woodland seems to be the preferred choice in Northern Europe though nesting sites in coniferous forests are not uncommon. Nestboxes need to be sited in one of the most mature trees in the woodland, preferably within the woodland itself rather than on the fringes. Fix your nestbox securely to a large tree as shown in Fig. 3. In a remote undisturbed area the box can be placed as low as 3 metres (10’) above the ground. In more populated areas or places where vandalism may occur, the box should be secured not less than 3.7 metres (12’) up or higher if possible. Try to face the box entrance away from the prevailing wind (generally this means avoiding the west or south-west).