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.
- The wood should be about 19mm thick (but no be less than 15mm). 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.
- Don’t choose a box made from thin wood, plywood, corrugated cardboard, plastic or solid ceramic materials. Although birds may occupy them if no other nest sites are available, they are unlikely to be successful. Also, boxes made from dense materials like ceramics can be dangerous since they are likely to be too hot or too cold for chicks to survive.
- 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.