Providing a bird box in your garden is a great way to support nesting birds, but choosing the right hole size is essential. Different bird species require different entrance hole sizes to ensure their safety and comfort. A hole that is too large may attract unwanted visitors or predators, while a hole that is too small might not be suitable for the birds you want to attract.
In this guide, we will explain the importance of bird box hole sizes and help you determine the best size for different bird species.
Why does the hole size matter?
The entrance hole size of a bird box determines which birds can use it. Birds select nesting sites based on their natural preferences, and the hole size plays a key role in this choice.
The right hole size ensures that:
- The intended bird species can enter and nest comfortably.
- Larger, more dominant birds do not take over the box.
- Predators such as larger birds or squirrels cannot access the nest.
- Competition between species is reduced, helping to maintain biodiversity.
By choosing the correct hole size, you increase the chances of attracting the right birds to your garden while keeping their nests safe.
Recommended bird box hole sizes
Here is a general guide to bird box hole sizes and the species they attract:
| Hole Size | Suitable Bird Species |
| 28 mm |
Great tit, tree sparrow, pied flycatcher, blue tit, coal tit, marsh tit |
| 32 mm | House sparrow, nuthatch, great tit |
| 45 mm | Starling |
| oval or open front | Robins, wagtails, spotted flycatchers |
| open front | Blackbirds, thrushes |
Note: These are general recommendations, and slight variations can still be effective.
How to modify an existing bird box
If you already have a bird box but want to change its hole size, you have two options:
- Use a hole reducer plate: These are metal plates with different hole sizes that can be attached over an existing entrance to adjust the opening. They also help prevent woodpeckers or squirrels from enlarging the hole.
- Drill a larger hole: If your current hole is too small for the species you want to attract, you can carefully enlarge it using a drill. Ensure the edges are smooth to avoid harming the birds.
Where to place your bird box
The placement of your bird box is just as important as the hole size. Follow these tips to ensure birds feel safe and comfortable:
- Height: Place the box at least 2-4 meters high for small birds and 3-5 meters for starlings.
- Direction: The entrance should face south-east or east to avoid strong sunlight and heavy rain.
- Shelter: Avoid placing it in direct sunlight or exposed locations. A tree or wall provides good protection.
- Distance: Keep boxes at least 3 meters apart to prevent territorial disputes.
- Accessibility: Ensure the box is easy to clean by providing a hinged side or removable front panel.
How to maintain a bird box
To keep your bird box safe and attractive to birds, regular maintenance is important:
- Clean the box annually after the breeding season (autumn is best).
- Remove old nesting materials to prevent parasites and disease.
- Check for damage and repair any cracks or loose fittings.
- Avoid disturbing the box during nesting season.
A well-maintained bird box will be used year after year, helping local bird populations thrive.
Choosing the right bird box hole size is essential to attract the right bird species and provide them with a safe nesting environment. By following the recommended hole sizes and placing your bird box in a suitable location, you can create a welcoming space for birds in your garden.
If you want to encourage biodiversity and support garden birds, consider adding a suitable bird box to your outdoor space today.