With the availability of good quality bird nesting boxes on the market these days, it is easier than ever before to supply hole nesting species of bird a place to nest.
However, in many situations (particularly woodland, orchard and scrub/tree clearance works) where a skilled chainsaw operator is in use on site, there is a very cheap alternative to traditional nest boxes fixed on tree trunks.
Please note: The following project can in theory be done with hand tools (chisels etc.) but is much easier with a chainsaw and power drill. Chainsaws must only be used by qualified and experienced operatives.
Where appropriate, any good sized tree trunk (approximately 200mm in diameter and above) can be easily transformed into a very natural looking nesting cavity.
First, decide on the final height of the trunk in question. There is no perfect height for this, but it is worth taking into account a couple of important points:
- Depending on the location, nest holes low to the ground may suffer from mammal predation (particularly weasels, stoats and cats)
- The higher the trunk, the more difficult the cavity is to work on safely with a chainsaw and power tools etc.
When you have decided on the appropriate final height, cut neatly with a chainsaw (or bow saw if you are feeling energetic!), creating a nice neat cut that is perpendicular to the trunk (see images below). When this is done, repeat the process at least 50mm below the first cut, effectively taking a nice slice off the trunk, giving you what looks like a large mug coaster.
Next, keeping dimensions fairly approximate, bore down vertically with the chainsaw four times to create an internal square, approximately 200mm to 300mm deep. Take extreme care when undertaking this as chainsaws are obviously very dangerous tools and are prone to what is referred to as 'kick back' when used in this way.
Now cut in the same way diagonally from corner to corner, and side to side. You will create something resembling a union jack flag series of cuts. By now some of these vertical slivers of wood will begin to come loose and can be removed. Continue carefully boring around in the hole until you are left with a square cavity with internal dimensions of ideally about 200mm x 200mm x 200 - 250mm deep. This is only a rough guide, nature is rustic after all!
Now pick up the slice from before which acts as the roof/lid, align it with the trunk the same way it grew before it was cut and drill a pilot hole approximately 5mm wide in the corner somewhere convenient (again, dimensions are only a rough guide here). Fix the roof/lid using a single long screw, say 100 - 150mm long, into the trunk but just tight enough so the roof/lid can be slid to one side for later inspection and cleaning out nesting material. An impact driver used carefully or a drill driver with the correct torque settings are best here. Be careful not to apply too much force driving the screw in and split the roof/lid.
Now drill a second hole through the opposite side of the roof/lid, perhaps up to 10mm in diameter, that goes through the roof/lid and at least 50mm into the trunk. Find a small hard stick just narrower in diameter than the hole, and cut or snap to length at least 50mm longer than the length of the hole. This can be a simple unobtrusive peg to keep the roof/lid in place, and it looks nice and rustic without using metal that will rust. Alternatively a short length of dowel would suffice.
The final and most satisfying task is to drill the hole into the cavity. Site the hole facing between North and East.
The width of the hole depends on the species of bird you are looking to attract:
25mm - Blue tit, Coal tit, Marsh tit
28mm - Great tit, Tree sparrow, Pied flycatcher
32mm - House sparrow, Nuthatch
38mm / 40mm - Starling, Redstart
A great tit can be seen using this windblown hazel coppice cavity a few weeks after it was made. A successful brood of chicks fledged amongst the regrowth.
Dense regrowth in the first year helps conceal nests; the cavity is actually on the left of this image hidden behind leaves!
That's the project complete. All there is to do now is enjoy and monitor any birds that breed (and roost) in your cavity, and if the trunk is alive cut back any regrowth that may pose problems to the birds, outside the breeding season.
We are currently trialing treecreeper nest cavities and hope to have a basic design to show a case study on in the next couple of years.
Whilst carrying out this type of project it is an obvious but necessary point to make not to destroy existing cavities. On the same woodland site where the above photos were taken we discovered this robin nest inside a rotting ash stump.
Text and images by Jim Ashton