Building a bird nesting box for your yard could be something that you are considering.
A nesting box needs to be large enough so that birds can enter easily, exit easily and comfortably nest, so how do you accomplish that when designing one yourself?
This project is a great opportunity for someone interested in creating a bird home, and even if you aren’t skilled in DIY home improvements, there should be no reason that you can’t make a beautiful bird box to attract all types of wild birds to your garden!
There are many factors to consider when building a bird box such as: size of entry hole, box dimensions, etc. If you aren’t careful your box will be too small to accommodate birds!
What Size Should a Nest Box Be?
There is no set size for a bird’s nest box, as it should be designed to accommodate the specific species of birds you wish to attract.
For example, if you want to attract larger bird species, such as pigeons and corvids, your nestbox must be larger than if you are trying to attract smaller bird species, such as blue tits or great tits.
This paper assumes that the target bird species will be small. However, it would be advantageous to look at the dimensions of different types of nest boxes based on the size of the bird species.
However, the size for the actual nestbox will be similar among small birds (robin, tit, nuthatch, sparrow, etc.) regardless of the type of bird.
When creating a nest box for a specific species of bird, it is important to adjust the hole size at the front accordingly. We will discuss this in more detail later in this article.
Additionally, the size of the nest box may vary depending upon the size of the young birds that are typically reared by each individual bird species.
General dimensions for small bird nest boxes are approximately as follows:
- 225mm high by
- 180mm deep by
- 180mm wide
Therefore, small birds should have enough room to create a suitable, comfortable nest for their young and to raise them without the risk of overcrowding.
Larger birds that require larger nest boxes, for example, barn owls, will require larger boxes as well as more room inside the box itself.
A barn owl nestbox should be approximately 670mm high, 570mm wide and 500mm deep, with an entrance hole measuring 400mm high.
As a rule of thumb, larger bird species will require larger nest boxes and their chicks will also be larger than small bird chicks.
At this time, there is no single size fit for all bird species nest boxes that can be supplied by any manufacturer. Nest box sizes are extremely variable across different bird species.
Therefore, before purchasing a ready-made nest box, consider both the bird species you are targeting and their natural nesting preferences, along with their specific requirements.
The following information on nest box sizes by bird species may be helpful; however, it does not include all bird types:
- Wren: 200 high by 200 wide by 180 deep.
- Tawny Owl: 770 high by 220 wide by 410 deep.
- Robin and Spotted Flycatcher: 200 high by 200 wide by 180 deep.
- Tree Sparrow: 210 high by 150 wide by 150 deep.
- Blackbird: 180 high by 300 wide by 150 deep.
- Jackdaw: 410 high by 200 wide by 200 deep.
- Nuthatch: 230 high by 190 wide by 190 deep.
- Kestrel: 340 high by 300 wide by 520 deep.
To stop the box from twisting, choose at least 15 mm thick plywood.
Plywood is also a barrier against heat and cold, providing insulation, thus protecting your chicks during weather extremes. Plywood should allow your bird box to hold up well over time (years) without splitting or rotting.
It is super critical that you do not neglect or disregard the size of your nest box!
How Big Should The Hole at The Front of a Nest Box Be?
When it comes to building your nest box, the size of the entry hole is one of the most important considerations.
That’s because different birds require different sized entry holes, and most birds prefer to have an entry that they can just barely get their bodies through.
By restricting access to their entry, you help prevent larger animals from entering the box after the birds have entered. This helps keep the birds safe as they develop into their vulnerable flightless juvenile stage in the box.
What size do you need for the entry hole?
If you are uncertain what types of birds you want to attract, the entry hole size should be 32 mm for small nesting birds, which is the standard size for domestic nest boxes.
You can create this size with a standard 32 mm drill bit, and this size will work well for many of the most common garden birds that may wish to use the boxes.
If you are looking to design your nest box for a specific type of bird, you may want to consider the space required for an adult bird of that species to get through the opening depending on the size of adult birds and the species of bird you are interested in attracting.
- Robins prefer open fronted nest boxes that are well covered by vegetation; an opening on the front rather than a small hole is better for them, as this will allow the robin to easily enter and exit the box. You may place a piece of wood across the front of the box to keep it securely closed and hold the eggs in, but it is best to leave the top half of the front of the box open in order to provide maximum access for the robin.
- Blue tits prefer a nesting box with a hole of about 25 mm, which is typically the smallest hole available for nest boxes. This size allows blue tits to easily enter the box, but does not leave enough space for the blue tit’s predators to enter the box.
- Next size up is the nuthatch, which prefers to have a hole approximately 28 mm in diameter. Although the nuthatch also prefers a small hole, it requires slightly more room than a blue tit.
- Great tits and house sparrows both like to nest in boxes with holes of approximately 32 mm in diameter because they are larger than either the blue tit or nuthatch and need to be able to comfortably enter and exit the box.
To attract house martins, place a cup-shaped nest under the eave of your home instead of using an actual box.
For starling nesting sites, use a large box that has a 45 mm entry hole.
How High Up Should The Hole Be?
The height of the hole is crucial because if the. height of the hole is not high enough then birds may not use the box
Predators may be able to remove the baby birds (chicks) if there’s not enough space between the hole and bottom of the box
Therefore, the hole should be a minimum of 125mm above the base of the nest box
The higher the hole from the base gives protection from predators (cats) being able to reach in and harm the baby and create a safe environment for the parents.
The hole should not be lower than 125mm, or the babies could get hurt
Roughen up or sand down the wood underneath the hole to give the babies something to grip on when they’re trying to get out of their nest box
Don’t make the hole distance much higher than 125mm or the babies will have trouble getting out
Some birds, like blackbirds and pied flycatchers, need a shorter hole-to-bird-basket depth
Many blackbirds will like 70 mm and most pied flycatchers need around 90 mm to get out of their nest boxes.
In general, a larger gap is safer for chicks. If there is a smaller distance between the hole and the base of the box, you will have to be extra careful where you put your box so it is out of reach of cats.
What Else Should I Think About When Building a Nest Box?
Adding drainage holes to the nesting box is extremely useful for allowing moisture to escape.
By placing the holes at the bottom of the box, the temperature inside will not be affected significantly since no wind will enter through them.
If you do not have drainage holes in the box, there is a possibility that humidity may build up inside the box, causing mold.
You should not treat the wood with any chemicals, however, if you live in an area with consistent moisture, cover the box with leather or add a mini roof to divert rainwater away.
Covering the nestlings from rain will keep them dry and warm inside the box and will also help extend the life of the nesting box.
Additionally, consider having a detachable door on the front of the nest box to allow for easier access.
You may need to remove dead babies from the nesting box or other remains after the parents successfully hatch and raise the young chicks to maturity.
Even though the parents will do their best to keep the nest box clean of any remnants from dead chicks, it is likely that they will not be able to remove them after an older chick has died.
In nature, the dead chick would generally be eaten by a predator, but enclosed in a nesting box will prevent this from happening, so you will want to be able to easily access the inside of the box to remove any remains as needed.
Conclusion
To attract the birds that you want, ensure that your birdhouse is greatly oversized for the species and has an appropriate size entrance.
By providing your birds with a sense of security, you increase the chance that your birdhouse will be used year after year!
At the end of each season check your birdbox to ensure it is still safe for birds to use in the following year.
If any part of the birdhouse is worn or a part of the wood is broken, replace these items, or take the birdhouse down if you have any doubts about it being a safe place for birds to nest, even if you cannot immediately replace it.