Commercially available nest boxes come in a huge range of shapes and sizes, but beware: while some provide a perfect breeding cavity for birds, others are far from ideal. Here are our guidelines to help you choose wisely
- Only choose a box made from an insulating material such as wood or a special waterproof wood/concrete compound like WoodcretePLUS™ used for the National Nest Box Week “Official” Box.
- Don’t choose a box made from dense materials like metal or ceramics as the interior can become too hot or too cold for chicks to survive.
- To provide insulation and be durable, the walls of wooden boxes should be at least 15mm thick. Wooden boxes can be safely treated on the outside with a preservative provided it is non-toxic and water-based. A box made from cedar, oak or beech will far outlive one made from softwood such as pine
- Choose a box with a 32mm entrance hole as this is the ideal size for all small hole-nesting birds such as sparrows and tits. Choose a smaller 26mm hole only if you want to restrict the box to Blue Tits.
- The box should not be too small inside as birds may lay fewer eggs in smaller boxes. The internal floor area should at least 130 square centimetres (20 square inches).
- Perches are not necessary and may even act as a foothold for squirrels or weasels as they reach into the box to grab eggs and chicks.
- A good box should provide easy access for human observers who wish to record the contents and to clean out the disused nesting material at the end of the season.
- Don’t choose a box which is incorporated in a bird table as the nesting birds may come into conflict with the feeding ones.