Starling boxes and larger entrance holes

Most nest boxes sold for gardens are small-hole boxes for tits and sparrows. Starlings are bigger birds, and they need a bigger hole and a bigger box. This guide is about that step up, and about a confusion that comes with camera boxes: an entrance that is larger than a tit hole but is not a starling hole either.

The figures here come from two BTO pages opened on 14 November 2026: Putting up a nest box and Make a nest box. The starling background comes from the RSPB’s starling page, opened the same day. If a number is not on those pages, it is not on this one.

The starling figure

The BTO putting-up page says: “For Starlings try a box with a 45mm entrance hole.” That is the only starling hole size on the pages we opened.

The make-a-box page does not repeat the 45 mm figure. It says that larger species, “such as Starling and Jackdaw, need a larger entrance hole and a larger box”. It does not give the internal dimensions of that larger box. So this guide does not either. If you are building one, a box designed for a 25 mm or 32 mm hole with a wider hole drilled in it is not what the BTO is describing: they say the box needs to be larger too.

The small-hole sizes on the make page, for comparison, are 25 mm for blue, coal and marsh tits, 28 mm for great tits and tree sparrows, and 32 mm for house sparrows and nuthatches. The full table, and the BTO buying page that puts it slightly differently, are in the nest box guide. That guide covers the small boxes; this one covers the jump to 45 mm.

Why starlings are worth a box

The RSPB says starlings like to nest in cavities in trees and rocks, and often in the eaves or roofs of houses. They put the species on the Red List of UK Birds of Conservation Concern and describe it as an RSPB Priority Species. A garden box is one way to offer a cavity that is not in your roof space.

Starlings and house sparrows are often found in the same places on a building. If you are thinking about the eaves, the sparrow terraces and open-fronted boxes guide covers sparrows, which nest in loose groups, and the RSPB’s height and direction advice for them. A starling box is a single larger cavity, not a terrace.

The RSPB starling page also says their favourite foods are cranefly larvae and worms in short, grassy areas, and that they readily visit feeders for suet pellets and fat balls. A patch of short lawn nearby is part of what makes a site suitable, as well as the box.

Why a 38 mm camera box is not a tit box

Camera boxes are where the larger-hole question most often comes up. The Birdfy Nest Wood, compared in bird-box cameras, is stated by its maker as having a 38 mm entrance. That is the maker’s figure, not a BTO size.

Set it next to the BTO numbers:

• It is wider than 25 mm and 28 mm, the tit sizes on the make page.
• It is wider than 32 mm, which the BTO gives for house sparrows and nuthatches.
• It is narrower than 45 mm, the BTO’s starling hole.

The BTO pages we opened do not list 38 mm for any species. We are not going to guess which birds will take it. What we can say is that it is not the hole the BTO describes for blue tits, and it is not the hole the BTO describes for starlings. If you want a box for a particular bird, choose the hole from the BTO table first and the camera second. A camera you fit inside your own box, such as the 12 V camera on the same page, or a cable-free option in solar and cable-free bird-box cameras, leaves the hole size in your hands.

Where to put a larger box

The BTO putting-up page gives general siting rules for all boxes:

• The front should be vertical or angled slightly downwards, so rain does not get in.
• Shelter it from the prevailing wind, rain and strong sunlight.
• Make sure it is not easily accessible to predators, and that cats cannot get into it.

The page’s height figures (1–3 m on a tree trunk, with a heading that says about 3 metres) are written for small-hole boxes. It does not give a separate height for starlings, and we are not inventing one. Put it high enough to be out of a cat’s reach and clear of branches a cat could use. If a cat patrols the garden, read cats and garden birds.

The BTO says pairs begin to prospect in the latter half of February, and that it is never too early or too late to put a box up, because birds also roost in them.

Cleaning and the law

A larger box gets messier, and it still needs an opening roof or front so you can clean it. The BTO page says the law permits cleaning out nests between 1 September and 31 January. Outside those dates, and whenever a nest is in use or being built, leave it alone. The full rules, with the legislation, are in cleaning a nest box.

What size hole does a starling box need?

The BTO putting-up page says try a 45 mm entrance hole for starlings. The make-a-box page adds that starlings need a larger box as well as a larger hole, without giving dimensions.

Will blue tits use a box with a 38 mm hole?

The BTO pages we opened do not list 38 mm for any species. Their blue tit size on the make page is 25 mm. We are not going to predict who will use a 38 mm hole.

Can I just drill out an old tit box to 45 mm?

The BTO says larger species need a larger box as well as a larger hole, so a small box with a bigger hole is not the same thing.