How to make a bird box
The natural nesting sites which many of our beloved birds depend on are disappearing. You can provide much-needed alternatives by putting up bird nesting boxes.
The following design is ideal for sparrows and small songbirds such as blue tits. Read on to discover when and how to clean your bird box and more ways to help nesting birds.
You will need:
a frost-safe terracotta pot (otherwise it may crack in winter)
a piece of wood slightly bigger than the diameter of your pot
a round file
(optional) a couple of short pieces of hose pipe
1. Turn your pot upside down and use the file to enlarge the drainage hole to a suitable entrance size (see below to find out how big to make it).
2. Put the pot on top of the plank of wood with the entrance hole facing outwards. Hammer four nails halfway into the wood, evenly spaced around the rim of the pot.
3. Twist thick, strong wire around each nail and the pot to hold it securely in place.
4. Find a quiet, sheltered location where you have permission to put up your nest box.
5. Use wire to attach your nest box to a tree, ideally so it faces northeast. Thread the wire that passes around the trunk though some hose pipe and use pliers to twist the ends of wire together. Your nest box is now ready for a bird to move in.
Attaching the pot to the wood with wire rather than glue will allow any water that gets in to drain out and also means you can remove the pot to clean it.
Using wire to secure your bird box to a tree means you can easily remove it to clean it or move it to a different location. It's also better than driving a nail into a living tree. You can adjust the wire each year so that it doesn't cut into the tree as it grows. Using hose pipe provides added protection against wire damage.
If you don't have a suitable tree in your garden, you could adapt our design to attach to a shed or wall instead, but make sure you can easily take it down for cleaning.
Why are bird nest boxes needed?
Fewer natural nesting sites are available to birds. Some species such as robins, blue tits and blackbirds have been badly affected by a loss of hedges and trees from gardens as well as increasing urbanisation. House sparrows, house martins and swifts have all lost out to the repair of old houses, and modern building styles and regulations, which have reduced the number of holes, nooks and crannies where they can build nests.
The number of house sparrows has fallen dramatically in Britain, particularly in urban and suburban areas. The loss of suitable nesting sites is a potential factor.
Museum ecologist Steph West says, 'We think of house sparrows as our ubiquitous town bird, but increasing pressures, such as more predatory pets like cats around and gardens becoming increasingly inhospitable to wildlife over the years, have caused a decline in population.
'Anything we can do to support somewhat beleaguered wildlife like our sparrows is fantastic.'
How big should the hole be in a bird box?
If you're not sure what bird species in your area are most in need of nesting boxes, a diameter of 32 millimetres is good for all common birds that nest in small holes. But smaller species such as blue tits who move in may get ousted by larger, more dominant species. You can help them avoid eviction by providing a smaller hole.
As a general guide, make the hole size:
- 25 millimetres for coal tits, marsh tits and blue tits
- 28 millimetres for great tits, tree sparrows and pied flycatchers
- 32 millimetres for nuthatches, house sparrows and redstarts
Rats and weasels are a threat to young birds. They can chew bigger holes into wooden nest boxes and get to the eggs or chicks. Our design should reduce this risk.
Steph West works in the Museum's Angela Marmont Centre for UK Biodiversity. She has more than 20 years' experience as an ecologist and part of her current role is to help people study and record UK wildlife.
While you can never guarantee a nest box will be used, Steph says there are two things you can do to increase the chances:
- Put it up in a safe position that is relatively close to shelter but not on regular cat routes. Place it as high as you can safely reach.
- Make the wider environment as inviting for birds as possible, with a variety of plants to provide shelter and fruit (which some species eat) and to attract insects (many species feed on invertebrates). Offer water - a bird bath or even a pond, which would also bring in more insects for birds.
Steph explains, 'Birds really need three things: a good food source, a safe nesting and roosting environment and a safe route between the two.
'Particularly in urban landscapes, one or more can be missing. You can help by providing a safe nesting position close to their local food "shops".'
Sparrows are colonial breeders, so they're more likely to choose to nest in a bird box if there are more nearby. Place a few nesting boxes close together - 'putting them up the trunk of a tree like a high rise is fine, or you could put them in a row on a wall or the side of your house,' adds Steph.
Read on for further advice from Steph on the best position for your bird box, when to put it up, how and when to clean it, and more ways to help your local birds during breeding season.
Where to put a bird box
The height of the nesting box isn't critical for many species. There are some exceptions. Coal tits prefer to nest low down, a metre or less above the ground. Sparrows and pied flycatchers prefer their nests to be at least two metres off the ground, nuthatches at least three.
'Most birds will prefer a box at least one metre above ground level,' says Steph. 'If there are inquisitive children or pets around, higher is better.
'As long as nesting opportunities are the element that is missing in the natural environment and birds feel safe enough, they will likely use nesting boxes you provide.'
Steph has these tips:
- Don't position nest boxes too close to bird feeders. All the activity can bother nesting birds.
- Avoid locations where foliage would conceal the entrance hole - the birds using this style of nesting box like to be able to scan for predators.
- Artificial lighting can disturb birds and affect their circadian rhythms. Bear this in mind if you have a security light, for example, and put your box somewhere that the light won't reach, or consider more wildlife-friendly approaches to lighting.
- Avoid placing your nesting box near areas where cats are likely to perch, such as the top of a wall.
Steph adds, 'If you own a cat, you can help your local wildlife by keeping your pet indoors at certain times of day when they are most likely to hunt - particularly in the evening and early morning, ideally overnight.'
Which way should a bird box face?
In the UK, our wind and rain typically come from the southwest. To help protect nesting birds and chicks from the rain, try to position your nesting box so that it faces northeast.
Avoid placing it in the direct Sun or facing a southerly direction. It would catch the strongest Sun and there is a risk that chicks inside will overheat.
When is the best time to put up a nesting box for birds?
It is best to put up your nest box as early in the year as possible, to give birds time to find it before they start breeding in spring.
National Nestbox Week, organised by the British Ornithological Trust (BTO), runs from 14 to 21 February every year. But some species will already be looking for suitable places to nest before this date.
Birds may also use nesting boxes as sheltered spots to roost in during cold periods or bad weather, so it's worth putting up new boxes as soon as they're ready.
Cleaning bird nest boxes
Nesting boxes can get a build-up of mites, particularly in places that don't experience freezing temperatures.
To clean your bird box, simply use boiling water and scrub it. The boiling water will kill viruses that can be spread between birds. It's a good idea to wear surgical gloves and a dust mask to protect yourself from any fungi and parasites present.
Don't use general-purpose cleaning products as these may contain substances that are toxic to wildlife.
Steph says, 'Nesting boxes don't have to be pristine before birds move in. They can also provide a good site for invertebrates to shelter in over winter, such as hibernating snails or certain butterfly species, including commas and peacock butterflies.'
When to clean out bird nest boxes
As soon as birds are nesting they mustn't be disturbed - they are legally protected by the Wildlife and Countryside Act 1981. Before moving your nest box to clean it, you must be certain nesting has finished and fledglings have left.
Steph adds, 'While the normal breeding season is March to September, some birds may keep going for longer. So it is a good idea to leave cleaning until winter. Monitor the box for several days to be certain that nothing is using it.'
It is illegal to keep or sell any abandoned unhatched eggs.
Should I put anything in my bird box?
No - allow birds to source their own nesting material.
How can I tell whether my nest box is being used?
The most obvious sign is seeing birds going in and out regularly. Droppings underneath are another clue and, as chicks get bigger, you might hear chirping.
How best to watch your new avian neighbours
Make sure you don't get too close - watching from behind a window is best. If you do watch from outside, stand against vegetation so that you don't have an obvious silhouette. Try using binoculars. It's also a good idea to wear earthy tones and avoid blue, which can stand out more to wildlife.
You may wish to install a trail camera outside your nest box so that you can record birds coming and going. Do this before birds move in or you risk disturbing them and the nest being rejected.
What to do if your nest box isn't used
Make sure you've chosen a suitable location following our guidance above.
Leave the nest box up for a few years, as it can take time for birds in the area to get used to it and consider it a safe option.
If it still hasn't had any inhabitants after three years, try moving it to a new position.
Steph adds, 'Don't get disheartened: it may mean there are plenty of good nesting spots in your local area for the number of birds present. Instead you could look for other ways to improve the wider environment and increase the bird population in the area - by growing plants that will increase the shelter and food (fruit and insects) available to birds, for example.'
You could also try putting up different styles of nest boxes to attract different species.
Different styles of nest boxes
Some birds, including robins, wrens and pied wagtails, prefer open-fronted boxes. Others such as barn owls, swallows and house martins need much larger holes or have special requirements.
You can find out more about suitable nests for these birds on the official National Nestbox Week website, and the BTO nest box guide PDF (3MB) includes an open-front design for robins. The RSPB also provides useful guidance on nesting boxes for birds as does the Wildlife Trust.
More ways to help birds during breeding season
Steph advises, 'If you rake moss from your lawn, leave it somewhere for birds to collect. Many species use it as nest material, including robins, blackbirds and various finches.
'Birds will also use dead leaves, lichen and twigs, so don't be too tidy in your garden.
'You could even provide wool (not artificial fibres) or horsehair. Don't put it in netting as birds can catch their feet.'
Leaving areas of damp mud will help house martins, if there is a building with eaves or an overhang nearby. Blackbirds and song thrushes will use it too.
If you can, grow shrubs and trees - these offer cover for birds to hide and shelter in, as well as potential nesting sites. Hawthorn, ivy and wild roses provide the thick vegetation ideal for house sparrows to hide, rest and socialise in.
In spring and summer, birds will be searching for insects and grubs to feed their chicks. Wild areas filled with native plants will help to ensure there are plenty to eat. You could also supply mealworms.