Building a Nest Box

Watching birds nesting in your garden can be very rewarding, especially if they are in
a purpose built nestbox. Tits are particularly happy to use boxes and are always a delight.

Why build nest boxes at all?
Nestboxes are excellent substitutes for the holes found in old trees. In many parks and
gardens there may be plenty of food for small birds but nowhere for them to nest.

Which birds will use a nestbox?
Over 60 species are known to have used nest boxes, including of course blue and great tits. Among the others are coal tits, nuthatches, house and tree sparrows, starlings, spotted flycatchers, robins, house martins, kestrels and tawny owls. Much depends on where your box is and on your surroundings. For comprehensive information on nestbox design, see Nestboxes by Chris du Feu, BTO guide 23, obtainable from the National Centre for Ornithology/ The Nunnery, Thetford, Norfolk. IP24.2PU.

How do I make a nestbox?
Natural tree holes do not come in standard sizes, so use the following dimensions only as a guide. Use a plank of wood about 150mm wide and 15mm thick. The size of each section to be cut is shown on the digram. The inside of the box must be at least 100 mm square and the bottom of the entance hole must be at least 125mm from the floor. If it is less, young birds might be scooped out by a cat.
Use galvanised nails or screws. The inside front surface should be rough to allow the young birds to clamber up. Drainage holes shuld be drilled around the edge of the base.
The entance hole size depends on the species you hope to attract: 25mm for coal, marsh and blue tits, 28mm for great tits and 32mm for nuthatches, house and tree sparrows.
Hinge the lid with a strip of leather or rubber (an old piece of bicycle inner tube would do). Do not nail the lid down but use a good catch to fasten it. You will want to clean out the box in Autumn.
The same box with the upper half of the front taken away altogether may attract the occassional robin, pied wagtail or wren to nest. Spotted flycatchers prefer an even shallower, open-fronted box.

What can I use to treat the wood?
Softwood boxes may be treated with water-based paints such as Fenceguard. Apply any wood preservative only to the outside of the box, and not around the entance hole. Whatever you use, make sure the box dries and airs thoroughly before putting it up.

Where should the boxes be placed?
Fix the box two to five metres up a tree or wall, out of the reach of cats and curious humans! Unless there are trees or buildings which give permanent shelter, it is best facing between North and South-East, thus avoiding strong sunlight and the wettest winds. Tilt the box forward slightly so that any driving rain will hit the roof and bounce clear. House sparrows and starlings will readily use nestboxes placed high up under the eaves and these will often deter birds from nesting in your roof! But keep away from areas where house martins normally nest.

Further reading
Flegg. J. The Blue Tit. Shire Publications (Shire Natural History series) 1979.
Smith. G. The Joy of Wildlife Gardening. RSPB 1989.
Gosler. A. The Great Tit. Hamlyn 1993.

Acknowledgements
Drawing: Great Tit at nest box by Dan Powell
Text for article from RSPB leaflet Nestboxes for small birds.