That depends on the type of nestbox you have. If you have a ‘traditional’ type of nestbox then it depends on the size of the entrance hole: Blue Tit and Coal Tit will use nestboxes with a 25mm diameter hole, Great Tit and Tree Sparrow will use it if it has a hole of 28mm and House Sparrows use nestboxes with entrances of 32mm diameter. House Sparrows will also used ‘terraced’ nestboxes – which are essentially two or three nestboxes joined together. Starlings will use nestboxes if they have an entrance of 45mm and are around 25-30% bigger than the average nestbox.
If you have an open-fronted nestbox then it might attract Blackbirds, Robins or Wrens to nest. Blackbirds require a mostly-open front, Robins are okay with something half open, and Wrens will use something a bit more closed up.
In addition to the ‘traditional’ style of nestbox there are specialist nestboxes available for species like Treecreeper, Jackdaw, Barn Owl, Kestrel, Grey Wagtail, Dipper, Swallow, House Martin and Swift.
See the BirdWatch Ireland shop here for a variety of different types of nestboxes.
