Gardening: Home is a box with a hole

Putting up nest boxes gives a lifeline to birds. By Daniel Butler

As you peruse the seed catalogues indoors in the warm, spare a thought for birds. For many species, a lack of nest sites is the principal limit on numbers - and now is the time to put up nest boxes. Most gardens offer reasonable supplies of food for birds, but the majority lack safe refuges for breeding because the holes required by many birds are normally found in old and diseased trees which are in short supply in our carefully managed modern environment.

Man-made boxes can fill this gap, and can be bought from pet shops, garden centres and by mail order from the RSPB (prices start at around pounds 5). Home- made versions are just as welcome to prospective inhabitants. Patterns can be obtained free from the RSPB, but most people with a modicum of DIY ability can design and up knock up their own. For fastidious craftsmen, a six-foot plank will provide all the wood needed for a perfectly adequate box, while recyclers can make costless versions from scraps of wood and a few galvanised nails. The size and dimensions will depend on the timber, but the box should allow you access to aid cleaning next winter (a piece of old inner tube works well as a lid hinge).

Although almost any small container may attract visitors, every species has its own tastes. Boxes with round entrance holes of about 1in (25mm) diameter tend to attract the smaller tits, while nuthatches and sparrows can fit through 11/4 in (32mm) entrances. Others, such as wagtails, tend to prefer "rooms with a view" - boxes in which half the front has been cut away.

More ambitious bird enthusiasts can aim for rarer visitors. Woodpeckers like bigger versions of the standard box, but as a refinement these should be filled with expanded polystyrene (they like to excavate their own hole). Larger still are barn owl and kestrel boxes, this time lying on their sides and about 2ft x 1ft x 1ft (60cm x 30cm x 30cm). Tawny and little owls prefer even longer tubes, tied at an angle to the tree trunk. All these nest boxes can be made reasonably cheaply from sheets of outdoor ply.

Treated timber is theoretically safe for birds, but it is best to verge on the side of caution, so any preservatives should be water-based and used only on the outside of the finished box. Much the biggest threat to nesters comes from predators, however, which in most urban gardens are cats.

To save distress, hanging boxes between 6ft and 12ft off the ground gives an element of protection from cats while saving the well-wishing gardener undue personal risk from teetering at the top of a ladder. Tree-mounted boxes gain extra protection if barbed wire or thorny cuttings are wrapped around the trunk. Similarly, to avoid harming valued plants, it is best not to use nails, but to wire boxes to trunks or limbs, using tubing to prevent bark damage.

For the best rewards, place several boxes around the garden. In general, most birds prefer to avoid direct sunshine and prevailing winds hitting the entrance hole head on, but they can be fickle creatures. The most expensive, carefully positioned, well protected shelter is often ignored in favour of an apparently inferior site. Nevertheless, the effort put in now will be rewarded with cheerful birdsong in a few months' time.

National nest box week is being promoted by the British Trust for Ornithology from 14 to 21 February. An information pack costing pounds 2.95 (cheques payable to National Nest Box Week) is available from NBW, Freepost 1155, Canterbury, Kent CT3 4BR. Alternatively, the RSPB has two free booklets and sells a range of ready-made boxes by mail order. Write to Nest Boxes, N3436, The Lodge, Sandy, Bedfordshire SG19 2DL.