Nesting boxes for cavity-nesting birds

With nesting boxes we can help those birds that depend on caves for breeding. However, there are limits. Nest boxes only help a species if it also has the right habitat and food available to it. Unfortunately, this is not usually the case with our most endangered nest box inhabitants: hanging up nesting aids alone is hardly enough to save Little Owls, Hoopoes and Wrynecks. On the other hand, we can encourage the tits and a few other species, especially where the natural supply of caves is scarce. Well-built nest boxes also enable above-average breeding success.

Where can nesting aids be placed?

  • in gardens
  • on facades
  • in orchards and parks
  • in forests
  • at the edge of wetlands

How many nesting aids are useful?

The number of nesting boxes depends on this,

  • how many birds of cavity-nesting species can find food and shelter in the area in question. The leaflet "Bird-friendly garden" shows how to improve the surroundings of one’s own house in this respect. It is available from the Swiss Ornithological Institute and BirdLife Switzerland.
  • which species you want to promote: the larger they are, the more space each breeding pair needs. The more similar the different species use their habitat, the more likely it is that fights will occur in a confined space, z.B. for closely related tit species. Therefore, the following rule of thumb applies: the more different the hole sizes of the suspended nest boxes are, the more bird species come into question as users and the more nest boxes make sense.

Use the following numbers as a guide:

  • Garden: 1 nesting box on every second tree; boxes not occupied with nests have significance as overnight roosts.
  • Orchards and forests: up to 30 per 10 hectares.

Which locations are suitable?

Nest boxes are a substitute for natural tree cavities. The latter come in all heights, sizes and exposures. Therefore, you can be somewhat flexible in the construction and hanging of the boxes, depending on circumstances.

The ideal height for smaller bird species is between 1.8 and 3 meters (see table). Where vandalism is likely, it is better to hang the boxes a little higher. Turn the entrance holes away from the weather side and point them toward the east or southeast if possible. Nest boxes should never be exposed to full sun for long periods of time, but should hang in the shade or at least partial shade during the day. On the other hand, if the morning sun warms the box a little, this is an advantage.

Dimensions for nesting boxes of model 1 (data in cm, wood thickness 2 cm):

Blue, marsh, crested and pine titmouse

Great tit, pied flycatcher, tree sparrow,
House sparrow, nuthatch

1-2 × 32 mm or
1-2 × 30 × 50 mm
(vertical oval)

* Dimensions for Model 1 nest boxes (in cm, wood thickness 2 cm). The dimensions given should be regarded as minimum values. If more space is available when designing nesting sites on buildings, external dimensions of 30 × 40 × 50 cm have proven successful, whereby the orientation (high or across) does not matter.

How to install nesting boxes?

It is best to hang nest boxes on branch stumps (z.B. with a wire hanger or plastic cord), so that they can be easily removed for annual inspection and cleaning. You can lean them against the trunk or – in wind-protected places – also let them hang freely from a side branch. They thus become more cat-proof. Do not use nails or thin wires on live trees.

When to install the nesting boxes? When to clean them?

Nesting boxes should be installed at the latest in early spring, but preferably already in late summer or autumn, so that the birds can become familiar with them at an early stage. In addition, the nest boxes offer them protection from wetness and cold in winter. The annual cleaning should take place between September and the end of January. In the process, the boxes are cleaned of nests and droppings. Normally dry brushing is sufficient for this purpose. Frosty temperatures on the cleaning day prevent any parasites from "overflowing" onto yourself. In the case of heavy parasite infestation, you can smoke out the box with a burning newspaper or rinse it with hot soft soap water and let it dry well. If you have determined that the young have fledged correctly, you may remove the nest immediately afterwards. The box is then available for a possible subsequent brood again in clean condition.

How to build nest boxes?

For nesting boxes, 20 mm thick, unplaned spruce or fir wood is usually used. Plywood or pressed boards are not breathable enough and therefore unsuitable. In wet years, this could lead to increased mortality among nestlings or even breeding abandonment. Screws hold the wooden parts together better than nails, especially in the long run.

If you want to protect the exterior surfaces against moisture, fungal and insect attack with an impregnation product, we recommend using a biological product, z.B. Linseed oil.

An obliquely drilled entrance hole rising inwards prevents rain from entering. A perch under the entrance hole is not necessary.

Boxes must be able to be opened for cleaning. The technically simplest solution is a movable front wall (model 1) or rear wall (model 2). For ventilation and dehumidification, drill at least 2 holes of approx. 5 mm diameter. When cleaning, make sure they are not clogged up.

A galvanized sheet metal plate with well ground edges around the entrance hole protects from woodpeckers.

The redstart appreciates a certain amount of light coming into the interior of its nest box. You can achieve z.B. with 1-2 highly oval, but still starproof, flight holes of 30 mm width and 50 mm height, with 1-2 round 32 mm loopholes or by making additional 1-3 holes of max. diameter above a round 32 mm loophole. Drill 20 mm into the front of the box.

Which model?

We have outlined two proven models. Model 1 shows the most widespread and easiest to make box. Model 2 is practically only used for hole sizes up to 32 mm, but has clear advantages: Thanks to the anteroom, the adult birds do not reach the young directly. This way they suffer less from the wetness brought in during bad weather and can get out more easily when flying out. In addition, the porch protects the brood better from cats and martens.

Where to buy nest boxes?

Nesting boxes are available from the Swiss Ornithological Institute (only model 1), from bird protection associations and here and there in workshops for the disabled, at the Landi and in horticultural centers. When buying a nest box, make sure that it meets the criteria listed here (minimum dimensions, flight hole size, wood quality, etc.).) fulfill.

Unwanted guests?

Nesting boxes are attractive for many different animal species. It is not possible to predict which species will eventually use them. So nesting in a "tit box" with 30 mm hole diameter z.B. gladly also house sparrows. Hornets, wasps or bumblebees can settle in the box. Especially in forests dormice or hazel dormice, occasionally even bats like to move in. These animals also have a right to exist. Therefore we recommend to tolerate them.

Nesting aids for other species?

Model 1 can also be built for larger species such as starling, stock dove or tawny owl. If necessary, use thicker wood for larger boxes and adjust the dimensions accordingly.

For more special nesting aids (kestrel, swift, barn owl, dipper, wryneck, hoopoe, etc.).) please contact the Swiss Ornithological Institute or BirdLife Switzerland.

Bird species
Recommended hanging height
High altitude propagation
Nest building start

Imprint: Leaflets for bird conservation practice

© Swiss Ornithological Institute& SVS/BirdLife Switzerland, Sempach& Zurich 2000, revision 2019
Author: H. Schmid
Copying with source reference is desired.

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