Do different species prefer different apertures of access hole?
Yes they do. This one has a 30mm diameter hole so it’s a versatile size that will suit a wide variety of birds. However if you want to target specific species then it’s possible to alter this. BTO has detailed information about how to make nest boxes suitable for a wide range of our native species. A 25mm hole will be suitable for blue tits, coal tits and marsh tits. They will use boxes with larger holes but there’s a risk they’ll be pushed out by larger, more dominant birds. If you want to adapt your box to be suitable for these species, you can use the detachable front panel as a template and cut a section of wood to the same dimensions, then bore a smaller hole.
Great tits and tree sparrows select nest box openings that are 28mm or greater. According to the BTO house sparrow and nuthatch select boxes with holes 32mm or greater. They know what they are talking about, they’ve been around since 1932. Some birders state that nuthatches and sparrows will go through the 30mm hole but if you want to be sure of making it suitable for these species then you can enlarge the hole a little.
Does it matter about the shape of the open-fronted nest box?
The main thing is the size of the opening. If you are sure you want to attract robins, blackbirds, wrens and wagtails then select the open fronted bird box. However if you want to have the option of open or closed, then this style is ideal, especially if you are buying it for someone else.