Nest box maintenance
Bird boxes should be cleaned out in the autumn when there's no risk of disturbing the occupants. Diseases and parasites can easily spread to new occupants.
To clean the box out use boiling water or buy specialised cleaning products from a local garden centre. Ensure the box dries out thoroughly before replacing the panels you removed in order to clean the box.
Do not use insecticides or flea powder. Do not breathe in the dust from the nesting material or dried droppings.
Your box may not be used in the first year, as birds often choose a nesting site during the autumn, winter or early spring. Persevere - leaving your box up in winter may provide a useful roost in bad weather.
If you find unhatched eggs in the box you can only legally remove them between October and January and they must then be destroyed (Wildlife and Countryside Act 1981).