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Blackbird perched near unsuitable nest box mounted in tree

Blackbird nest box size guide

Blackbird boxes are far larger than those for small common garden birds, but the size is easier to work with for attracting Blackbirds to nest.

Blackbird nest box size should have a maximum 300mm width with a 200mm height - with a depth that measures up to the height. Larger boxes adopt the height and depth, but it can be as little as 200mm in width if need be. That then means the entrance hole height would be just 100mm.

While there's no guarantee what size a bird box should be, one for use by a Blackbird is far larger, more open - but easier to access for cleaning out.

Shoot for a wider Blackbird box as I've primarily explained in detail using these dimensions as my recommendation.

That is not to say it can be a smaller,a more square shaped bird box overall.

Blackbirds are medium size garden birds so need the space, I therefore believe going for the biggest possible size can only attract more Blackbirds to it.

What is important to a Blackbird is its a safe bird box to nest in, so they will be the ones to make the final decision.

Its important the depth and height is identical for design purposes only, but the width can seem more than what is needed.

Its not but a more square shaped nest box can be used providing it uses that large bird box hole size that Blackbirds require.

300mm wide rectangular shape

When setting out to build or buy a blackbird nest box, make it one with a minimum internal width of 300m wide.

This minimum width would in turn correlate to a rectangular shape box.

Far larger than any bird box for small garden birds for sure, but remember as a common bird, the Blackbird is not classed as a small garden bird, but more so a medium size.

Internal measurements only mind so in building or locating a bird box for a Blackbird, you can add as much as 30mm to the width to take into account of the insolated side walls.

Blackbird nest box sizes can vary greatly, and be just as effective from one box to the next. To go for a more rectangular box are more common to buy, whereas a smaller square, yet taller box is made available.

200mm height allowance

Minimum height of a Blackbird nest box is important as this bird species is large after all, so needs the room to spread his or her wings.

Make it a minimum height then of 200mm if buying or building a bird box with a flat or slanted roof, but to use a bird box with an angled roof - you'd need to add as much as 45mm to it, where the extra height could be open or closed.

Height relates to an approximate 100mm entrance hole height, with a corresponding 100mm panel below it where birds nest behind on the other side of it.

That then gives us the total 200mm height figure, but to give or take several millimetres is perfectly within reason.

Height allowance is not a number that has to be matched, it completely depends on the bird box design.

200mm minimum depth

What applies to a bird box for Blackbirds is the all important depth needed to make sure its a spacious, comfortable wooden bird box where birds can nest in season.

No exact measurement needed but an approximate size must be considered - as you don't want to run the risk of it being too small or to large.

Play it safe then with a minimum depth of around 200mm, give or take a millimetre.

What you would find with the larger than normal bird box, is the one that is a more square shape to have more depth - whereas the much wider, rectangular shaped Blackbird nest boxes to have less depth.

Its probably to do with the design only, while not really serving a nesting purpose.

And that's why this 200mm minimum depth matches up to the height of the bird box.

Shape or size difference

Rest assured, Blackbirds nest in boxes regardless of shape, but size can have a say as too small can be restricted, or to large can invite predators.

Blackbird nest boxes can therefore be built or bought in all shapes and sizes.

First there's the more square shaped bird box which is more restricted for sure, but can look more pleasing if setting up in the garden.

Whereas a larger bird box for Blackbirds would usually go wider, up to twice as big - so rather than a larger square shape - it would be far wider.

All this of course means a more open bird box style so human observation is done so a little easier.

Bird boxes for Blackbirds that use a shallow base, with only 2-3cm high panel to secure their nest behind, should probably be avoided for the nesting birds sake.

100mm only front-panel

While the size of the front would usually measure up to the sides and rear of the bird box, remember there must be an wide, open fronted entrance hole made available.

Its therefore imperative there's a generous hole size for Blackbirds of 100mm, so this 10cm high hole can be used as a place to enter and exit.

And while this entrance hole is larger than a Robins or Wrens bird house, it can be used by either species - so don't be surprised if they do indeed use the Blackbird nest box.

Design is different with a Blackbird bird box too, as the wide open entrance hole can indeed carry on around the sides, up to 40mm - so the box is completely open to the elements, just as Blackbirds like it.

As the nest box has a total height of 200mm, it could then have an entrance hole size as wide has 300mm - or 200mm wide for a square ratio.


Minimum Blackbird nest box size can be approximately 300mm wide by 200mm tall, but only if using the largest boxes.

Large Blackbird boxes usually adopt the height, but width can be as much as 300mm, with a depth corresponding to the height only - if not a little deeper in smaller boxes.

Shape and size can vary from one box to the next if bought, but the aforementioned dimensions can very if building it yourself.

Bare in mind Blackbirds, much like any common garden birds; prefer to nest in a minimum size box to feel safe and secure - so success on its use can depend, but other species could end up using it instead.

Entrance hole size is an important factor, as its used for the hatchlings and parents to come and go. Make it a 100mm entrance hole height then, but the hole size width would normally correlate to the full bird box width.

Sitting below the entrance hole would be a 100mm or so panel, so in total the full height of Blackbird nest box would be 200mm.

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