Nest box & bird houses guide

Providing a safe and snug place for birds to roost and nest in your garden can be a very rewarding experience.

This guide will help you decide which bird house is best for you, how to clean your nest box and some curious facts around nesting birds.

Choosing the right nest box

Choosing a good quality nest box is important, as it will have an influence on whether your birds will use it.

Made from environmentally-friendly, durable timber, nest boxes should provide good insulation and ventilation, making them warm in winter and cool in summer.

Nest boxes for small birds

For smaller garden birds, nest boxes are excellent substitutes for the holes found in old trees. Regular hole-nesting birds include blue, great and coal tits, nuthatches, house and tree sparrows, starlings, spotted and pied flycatchers, robins, house martins, kestrels and tawny owls. Much depends on the type of the box, where it is located, and on its surroundings.

When choosing the right nest box for your smaller garden birds, you should look out for the size of the entry hole on your nestbox. A 25 mm entry hole is best suited for smaller birds, such as blue tit, coal tit and marsh tit. A 32 mm entry hole is suitable for slightly larger garden birds like great tit, tree our house sparrow, nuthatch and lesser spotted woodpecker.

32 mm entry holes can be protected from predators with a 32 mm nest box plate, or reduced to a smaller size using a 25 mm nestbox plate.

Nest boxes for birds of prey

For larger birds, such as barn or tawny owls, kestrels and other birds of prey, your nest box should have a landing shelf or perch, and possibly a fledgling exercise area for the youngsters to exercise their wings.

As some birds of prey, such as owls, are protected species, there are some things to look out for.
For example, barn owls are a Schedule 1 protected species and can only be inspected during the breeding season by someone with a licence. Outside the breeding season the nest box can be checked for maintenance and cleaning.
For advice on individual species, please read the information on the packaging of your nest box.

Where to position your nest box

Where to position your nest box depends on the species the box is intended for. Nest boxes for tits, sparrows or starlings should be fixed two to four metres up a tree or a wall.

Unless there are trees or buildings which shade the box during the day, face the box between north and east, thus avoiding strong sunlight and the wettest winds.
Make sure that the birds have a clear flight path to the nest without any clutter directly in front of the entrance. 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. Since these birds nest in loose colonies, two or three can be sited spaced out on the same side of the house. Keep these away from areas where house martins normally nest.

Open-fronted boxes for robins and wrens need to be low down, below 2m, well hidden in vegetation. Those for spotted flycatchers need to be two to four meter high, sheltered by vegetation but with a clear outlook. Woodpecker boxes need to be three to five meter high on a tree trunk with a clear flight path and away from disturbance.

Making your nest box weatherproof
If you would like to protect your nest box from harsh weather over the winter month, you can use a water-based preservative paint (preferably one that complies with standard EN71 part 3 as safe for children's toys). This type of paint/preservative is clearly marked on the container, and is usually available from DIY stores and hardware shops. Please make sure you apply the paint only to the outside of the nest box andonly in winter, when there is a low likelihood of occupancy. This will allow time for any remaining volatile components to evaporate.

As fixing your nest box with nails may damage the tree, it is better to attach it either with an aluminium screw, a nylon bolt or with wire around the trunk or branch. Use a piece of hose or a small section of bicycle or car tyre around the wire to prevent damage to the tree. Remember that trees grow in girth as well as height, and check the fixing every two or three years.

Two boxes close together may be occupied by the same species if they are at the edge of adjoining territories and there is plenty of natural food. While this readily happens in the countryside, it is rare in gardens, where you normally can only expect one nesting pair of any one species. The exceptions to this are house and tree sparrows and house martins, which are colonial nesters. By putting up different boxes, several species can be attracted.

The best time to put up a nest box is autumn. Many birds will enter nestboxes during the autumn and winter, looking for a suitable place to roost or perhaps to feed. They often use the same boxes for nesting the following spring. However, this depends on each species. Tits will often not seriously investigate nesting sites until February or March.

Cleaning your nest box

The nests of most birds harbour fleas and other parasites, which remain to infest young birds that hatch the following year. We recommend that old nests be removed in the autumn, from August onwards once the birds have stopped using the box.

Rinse the inside of your nest box briefly using boiling water to kill any remaining parasites, and let the box dry out thoroughly before replacing the lid. Please make sure you avoid melting any glue that may have been used in the nest box's construction, and do not use insecticides and flea powders.

If you place a small handful of clean hay or wood shavings (not straw) in the box once it is thoroughly dry after cleaning, small mammals may hibernate there, or birds may use it as a roost site.

It is quite normal for a few eggs to fail to hatch, or for some young to die. Blue and great tits lay up to 14 eggs to allow for such losses. Cold weather and food shortage may lead to nest desertion, or to only the strongest young surviving. The death of one parent or interference from animals or humans may also cause desertion.
Unhatched eggs in your nest box can only be removed legally between August and January - and must then be disposed of.

Avoid inspecting nestboxes in use, however tempting it may be to take a peek. Simply watch and enjoy from a distance. Only open it up if you've got appropriate skills and experience and are taking part in a monitoring project, such as the BTO’s Nest Record Scheme. If you want to see the chicks as they grow, you could consider installing a nest box camera before the breeding season starts.

Top tips
- Birds aren't the only things that like to enter nestboxes. Predators such as cats, squirrels, rats, mice, stoats, weasels, woodpeckers and members of the crow family also enter nest boxes. As predators mainly hunt early in the morning, most people are unaware of their presence. A metal plate fixed around the entrance hole may deter woodpeckers and squirrels, while barbed wired, gorse or rose clippings above and below the box will give some protection against most mammals, such as cats.
- Bees, wasps or earwigs will, on occasions, take over nestboxes and there is little one can do to prevent it - apart from using insect sprays. As many of the insects are useful food for birds, it is best to leave them alone. Insects often move in after birds have finished nesting. It is not unusual for the same type of insect to return to the box in subsequent years. Leave that box in situ and put up another one a few feet away. It is rare for both to be lost to insect invasion.
- Birds such as sparrows and starlings often take over nesting holes used by tits. Most tits are able to defend a box successfully, provided that the intruder cannot get inside. A hole size of 25 mm will exclude larger species.
- Do not fix a perch on the front of any box, as this will encourage intruders. Birds don't need a perch in order to use the box.
- Do not place sparrow boxes too close to ones intended for other birds, especially house martin colonies.