What makes a good nestbox?
It’s no surprise that shelter and security are the main hallmarks of a proper nestbox.
The best boxes are made from either wood or Woodcrete, a super-tough combination of sawdust and concrete. Both materials provide great insulation, ensuring that eggs and chicks don’t become too hot in the midday sun or too cold at night.
If you go down the wood route, boxes should be made using good quality timber that’s either new or recycled. The exact type isn’t vital, but a box made from hardwood like cedar, oak or beech will outlive one made from pine. Make sure the wood comes from a renewable source. There’s no point improving the habitat for your local birds at the expense of even more endangered habitats elsewhere.
The wood itself should be at least 15mm thick to offer sufficient insulation and prevent warping. Apart from the size of the entrance hole, box dimensions are not critical so adapt your plan to the wood available. Just ensure the hole is at least 120mm above the floor and that the box is large enough to accommodate your hand so that cleaning out nest material is easy to do.
Wood that is exposed to the elements needs to be protected. Use a water-based preservative, normally sold for sheds and fences on the market.
Perches aren’t necessary. They may even give squirrels and weasels a foothold as they reach into the box to grab eggs and chicks.
A hinged or removable nestbox lid is essential so that old nesting material can be easily removed at the end of the nesting period. It also allows easy access if you want to record the box’s contents.
Lastly, don’t choose a box that’s incorporated in a bird table. The nesting pair may spend too much time chasing off intruders and not enough catering for their own offspring.
Woodcrete is a tough and long-lasting alternative to wooden boxes.