Creating Real Estate for our Avain Friends

Posted on March 3, 2011


It’s not only humans that are struggling to find property in the economic downturn. Our avian friends are struggling too. Our love of over manicured gardens and woodlands together with making those long awaited home “improvements”, such as fitting new eves, leave little room for birds to establish nesting sites and can destroy ones that are habitually visited year after year.

Given that the sum area of our beloved gardens exceeds that of our nature reserves there is huge potential to create wildlife havens literally right on our very doorstep. It’s a tantalising prospect.

A great many of our U.K. birds have seen dramatic population declines for a variety of reasons, namely changes in land management practices and agricultural intensification which have reduced food availability, nesting and roosting sites. Long term change needs to be established if bird populations are to make a wholesale comeback but for birds that are happy to take up residence in nest boxes more immediate help is to hand. Us. Accompanied by a constant and suitable supply of food and water, nest boxes can aid the breeding success of some local bird populations.

Next boxes are widely available to purchase but it’s not all that difficult to make one especially when there are so many instructions about how to do so online.

When buying a nest box there are a few key things to bear in mind:

  1. Building material – Nest boxes need to be made from wood (ensure the wood is certifies FSC to ensure a sustainable future for forests). Plastic and metal can result in overheating and condensation build up.
  2. Thickness of walls – Walls should be no less than 15mm to provide good insulation and prevent warping.
  3. Water drainage
  4. Access for cleaning
  5. Perches – they are not needed and can facilitate access for predators if present2.

Whether you buy or make a nestbox of your own you need to have realistic aspirations about the residents you want to attract. There is no use putting up an extra large nestbox on the wall of a house situated in a very urban location and be disappointed when a pair of barn owl fails to move in. You need to consider what habitat you have to offer then choose according to the requirements of the species you want to attract. A good point to start is by identifying the species of birds you come across in the area you want to put up your nestbox. To help you match your chosen bird species with its requirements below is a table comprising of nestbox size and habitat requirements for the most common species that use nestboxes.

I need to stress at this point that the data in the following table represents generalisations. Some species are notoriously finicky with their requirements so it’s recommended to do some species specific research to be sure you are creating the right home for your potential avian neighbours.

Click for full sized table

For all species entrance holes need to be situated at least 125mm from the floor of the nestbox to prevent chicks from falling out and predators gaining easy access. The inside wall below the hole or panel opening should also be rough or have a series of shallow notches to enable fledglings to leave the nest. Each species has a preference for entrance hole size with the following diameters being advised2, 3:

  • 25mm – blue tit, coal tit and marsh tit
  • 28mm – great tit, tree sparrows and pied flycatchers
  • 32mm – house sparrows and nuthatches
  • 45mm – starlings

The same species differentiation applies for open fronted boxes whereby it is the height of the front panel that is important 3:

  • 60mm – spotted flycatchers
  • 100mm – robins and pied wagtails
  • 140mm – wrens

Commence Construction!

Now you’ve decided who you’d like as a neighbour and know what nestbox they need you’re ready to get down to business and build. The BTO, RSPB, Wildlife Trusts and bird groups have some good blueprints readily available online so the design phase is taken care of for you.

Building Material.

Wood is by far the material of choice with the thickness of the wood being no less than 15mm to prevent warping and provide insulation for inhabitants. Under NO circumstances should metal or plastic be used; these materials afford little insulation in cold weather, overheat easily and allow the build up of condensation within the nextbox. If you choose to build with new wood make sure it is from a sustainable source and look out for FSC certification. This reduces the chances of destroying pristine habitat elsewhere. Hardwoods are more durable than softwoods and therefore last longer. Avoid chromated copper arsenate (CCA) pressure-treated timber at all costs. If you can remember a little chemistry you’ll know from the name this isn’t nice stuff and the leachates may harm birds1, 2, 3.

To assemble the nestbox use galvanised nails or screws which don’t rust and not glue2.

As nestboxes need to be cleaned each year the lid cannot be nailed down. Instead attach the lid with plastic or brass hinges (because they don’t rust) and run a piece of rubber along the join (old bicycle inner tube is great for this). Fasten the lid down with a non-rusting catch1, 2.

Finishing Touches

Now you’ve constructed your nestbox there’s only a couple more things to do.

Nestboxes need to have some water drainage. Drilling a couple of holes into the bottom of the nestbox will allow any excess water to leave. This can be lifesaving if a considerable amount of rainwater happens to get in. Covering the top of the box with roofing felt can further waterproof your box1.

If you’re concerned about predation by woodpeckers or squirrels you can prevent the entrance hole from being enlarged by adding a metal plate. These are readily available in a variety of sizes.

Leaving the nestbox to weather naturally is the best option as it will blend in with the immediate surroundings better, offering some camouflage protectionPied fly-catcher chicks from predators. For softwoods treatment with water-based preservatives is an option but these need to be safe for animals. Sadolin and Cuprinol can be used but NOT creosote. DO NOT apply any preservative to the inside of the box or around the entrance hole even if it is deemed safe for animals. Ensure the nestbox is completely dry and well aired before putting it out for the birds1, 3.

Location, Location, Location

Species are not only fussy about nestbox size and habitat they also have different preferences for height, aspect, vegetation cover and the number of neighbours they will tolerate.

Do not place nestboxes in close proximity to a feeding station; the disturbance created by other birds may prevent its use.


Wherever you place your box the essential take home message is that it needs to be safe from domestic cats and inquisitive humans.

Nestboxes for tits, sparrows and starlings should be fixed at a height between 2m and 4m up a tree or on a wall. House sparrows and starlings will happily nest under eves but need to be away from nesting sites of house martins.

Nestboxes for robins and wrens should be placed below 2m, for spotted fly-catchers 2-4m high and for woodpeckers 3-5m high on the trunk of a tree4.


Nest boxes should be placed facing between north and east unless there is shelter from buildings during the day. This helps to prevent strong sunlight and wind and precipitation from hitting the nestbox. Additionally, nestboxes should be tilted slightly forward to allow rain to run off the lid and away from the entrance hole1, 4.

Flight Path

Always ensure a clear flight-path to the entrance of your nestbox1.


Again, the number of neighbours tolerated is species specific. House martins, tree sparrows, house sparrows and starlings are happy to nest close to one another but blue tits are not. They are fiercely territorial and have an average nesting density of 2 or 3 pairs per hectare1.

And Finally…

You’re ready to put your nestbox up! Huzzah!

However you put your nestbox up make sure you can access it for yearly maintenance. With this in mind it’s better to be able to remove the nestbox.

When placing nestboxes on trees different authorities and landowners have different preferences. Some don’t mind nails but others would prefer wire covered by some rubber tubing to protect trees1.

New nestboxes should be put up in February or March in time for the new breeding season.


Annual cleaning needs to be carried out each year, ideally in the months of October or November. Any old nesting material should be removed and the inside of the box doused on boiling water to kill any parasites waiting for next years inhabitants. Never use flea-powders or insecticides as these are not healthy for our avian friends.

If unhatched eggs are found in the nestbox they are only permitted to be removed from October to January and they MUST be destroyed. Removing eggs outside of the afore-mentioned period or keeping them is illegal under the terms of the Wildlife and Countryside Act (1981).

When you’ve finished cleaning your nest box don’t forget to pop it back into its original place. Nestboxes can protect birds from harsh weather conditions and can be used as roosting sites too1.






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