How to build a bird box

There is no standard, accurate design for a nestbox. Birds do not insist on their nest sites being mathematically precise! What they do require is a nest site which is secure and weatherproof, and as safe as possible from predators. So, make the box to suit the materials available, rather than buying materials to match any given dimensions. 

1. Mark out the panels of the future nestbox with pencil and a ruler, and write the name of each panel onto the marked out wood.
2. Saw the panels apart. You will need to make a slanted cut between the front panel and roof at a 45-degree angle 
3. Decide which box type you want to make and adjust the front panel accordingly:
   • Hole-fronted tit box – use a hand brace or drill to make a round entrance hole: 25 mm diameter for blue tits; 28 mm diameter for great tits; 38 mm diameter for sparrows.
   • Open fronted robin box – simply saw off 75 mm from the top of the front panel to make a ’window’ entrance.
4. Start constructing your box by nailing one of the sides onto the back plate through the back.
5. Nail on the floor (this can be quite tricky – go carefully to avoid splitting the wood).
6. Nail all the other panels into place except for the roof panel.
7. If your carpentry is of a high standard, with evenly proportioned panels and snugly fitting joins, you will need to drill some small holes (1-2 mm diameter) into the floor panel to allow for drainage.
8. Fix on the roof panel with a rubber flap ’hinge’ made from scrap rubber. This should cover the join between the roof and back plate completely, so it is waterproof. Nail the rubber into the back plate first, then pull it tightly over the join and nail it onto the roof. The roof should be able to lift away like a lid.
9. After construction, treat the outside of the box only with a water-based wood preservative product, such as 'Cuprinol' or 'Sadolin' (not creosote), to prolong its life and help repel water. If using planed timber, clear polyurethane may be used instead.
10. If you have it, fix a piece of roofing felt to the roof to prolong the life of the box and render it even more waterproof. 

Whether fixed to a tree or a wall, the height above ground is not critical to most species of bird as long as the box is clear of inquisitive humans and prowling cats. If there is no natural shelter, it is best to mount a box facing somewhere between south-east and north to avoid strong direct sunlight and the heaviest rain. The box should be tilted slightly forwards so that the roof may deflect the rain from the entrance.

You can use nails to attach the box directly to a tree trunk or branch; or you can use rope or wire wrapped right around the box and trunk (remembering to protect the trunk from the wire cutting into it by using a piece of rubber underneath it). Both methods are satisfactory, but obviously annual maintenance is easier if the box is wired and can be taken down easily for cleaning.

The number of nestboxes which can be placed in a garden depends on the species you wish to attract. Many species are fiercely territorial, such as blue tits, and will not tolerate another pair close by; about 2 to 3 pairs per acre is the normal density for blue tits. Other species, such as the tree sparrow, which is a colonial nester, will happily nest side-by-side.

Do not place your nestbox close to a birdtable or feeding area, as the regular comings and goings of other birds are likely to prevent breeding in the box.  

After the end of each breeding season, all nestboxes should be taken down, old nesting materials removed, and the box should be scalded with boiling water to kill any parasites. Do not use insecticides or flea-powders – boiling water is adequate. Annual cleaning is best carried out in October or November.

Under the terms of the Wildlife and Countryside Act 1981, if unhatched eggs are found in the box, they can only legally be removed from October to January inclusive, and they must be destroyed – it is illegal to keep them. 

How to clean nestboxes and bird feeders