Nestbox for birds, fixed to a tree trunk

Making and placing a bird box

Choosing where to place your nest box depends on the species the box is intended for.

Making a nestbox

Natural nest holes do not come in standard sizes, so use these dimensions only as a guide. Any plank or sheet of about 15 mm thick weatherproof timber is suitable. However, do not use CCA pressure-treated timber, since the leachates may harm birds. 

Dimensions

Our downloadable plan gives measurements for a small and a large box. Use only the first or the second figure throughout. For starlings and great spotted woodpeckers, use the dimensions for the large box; all the others need the small one.

The bottom of the entrance hole must be at least 125 mm from the floor of the nestbox. If it's less, young birds might fall out or be scooped out by a cat. The inside wall below the entrance hole should be rough to help the young birds to clamber up when it's time for them to leave.

Putting it together

Drill drainage holes to the base of the box, and use galvanised nails or screws to assemble. It's always best to leave the box untreated. As it weathers, it will blend into its surroundings. 

Softwood boxes can be treated with selected water-based preservatives, which are known to be safe for animals, such as Sadolin. Apply it only to the outside of the box, and not around the entrance hole. Make sure the box dries and airs thoroughly before you put it up. 

A woodpecker box should be filled with a block of balsa wood, rotting log or wood chips – woodpeckers like to excavate their own nesting cavities.

Do not nail down the lid, since you will need to clean out the box in the autumn. Attach the lid with a brass or a plastic hinge that will not rust, or hinge it with a strip of leather or rubber (an old piece of bicycle inner tube will do). Fasten it down with a good catch.

How big does the hole need to be?

The entrance hole size depends on the species you hope to attract: 

  • 25 mm for blue, coal and marsh tits
  • 28 mm for great tits, tree sparrows and pied flycatchers
  • 32 mm for house sparrows and nuthatches
  • 45 mm for starlings.

The small box with 100 mm high open front may attract robins or pied wagtails. A wren would need a 140 mm high front panel, while spotted flycatchers prefer a low 60 mm front to the box.

Choosing the location

Things to consider when choosing where to position your nestbox include:

  • 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. 
  • 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.
Blue tit, Parus caeruleus, perched on lichen covered branch in garden. Co. Durham

Attaching your nestbox

Before you put up your nestbox, remember to keep in mind the following:

  • Fixing your nestbox with nails may damage the tree. It is better to attach it either with a nylon bolt or with wire around the trunk or branch. Use a piece of hose or section of 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.
  • 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 2-4m high, sheltered by vegetation but with a clear outlook. Woodpecker boxes need to be 3-5m high on a tree trunk with a clear flight path and away from disturbance. 
  • Nestboxes are best put up during the 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. Tits will not seriously investigate nesting sites until February or March.
Birdbox on tree stump, RSPB Flatford wildlife garden, Suffolk