Nestboxes

The plot on Ardnamurchan is south facing hillside and was originally probably a mix of scrubby birch and oak woodland with dense ground cover of bracken. Over the years rhododendron have infested the site and, despite being cut back severely 10-15 years ago, still predominate.

I’m working hard to clear the rhododendron with the long-term goal of planting more native woodland. In the meantime I’m keen to improve the habitat in other ways that will benefit the local bird population.

Trees

As well as the dense and dreary understory of rhododendron, there are quite a few substantial trees around the plot. These include a number of mature (perhaps 40+ year old) larches, some Scots pine, quite a bit of birch and a few scattered rowan and hazel.

With the exception of the conifers, most of the trees are relatively small. Very few offer hole-nesting birds any real opportunities.

The future tree planting will be aimed at improving the pollen and nectar sources for pollinators (like bees, which need ample early season pollen for brood rearing) and the insect population. Caterpillars and larvae of the latter will boost the food available for the birds.

However, none of these new trees will provide any suitable sites for hole-nesting birds. At least not in the foreseeable future or, in the case of hazel and willow which will probably be coppiced, ever.

Nestboxes

Fortunately, the majority of hole-nesting birds readily use artificial nestboxes. In the ‘18/‘19 winter I’ve put up about ten in likely looking sites.

There are a huge range of nestboxes available to purchase, though many are pretty hopeless and are little more than garden ornaments. A nest box has to fulfil a couple of relatively simple functions:

• Protection to birds and nestlings from predators
• Protection from extremes of weather, in particular rain and excess temperatures

The physical and environmental protection is best served by using nestboxes made from robust materials, like 1" thick wooden planks. However, because of the high rainfall on Ardnamurchan, I’ve opted to use boxes made from a composite cement and sawdust mix. These are marketed under trade names like Woodcrete (from Schwegler) and Woodstone (from Vivara).

Woodcrete and Woodstone

If you mix sawdust and cement in the correct proportions (apparently about 3.5:1) and press the mixture into a suitable mould you end up with a hard stone-like material that offers excellent protection to birds and nestlings.

Woodcrete and Woodstone are essentially indistinguishable in terms of suitability for nest box construction and - for all I know - might come out of the same factory. They are completely impervious to water and, being stone-like, offers excellent insulation from excess temperatures. It won’t ever rot (and usually comes with a ten year guarantee) and it should be immune to even the most determined woodpecker.

Schwegler manufactures nestboxes from Woodcrete in a variety of designs. The majority of UK suppliers appear to have had low or non-existent stock for the last year. I therefore ended up buying Vivara boxes which are sold by CJ Wildlife and other suppliers, again in a wide range of designs.

I purchased a mix of nestboxes with 28mm, 32mm and 32mm oval entrance holes. These should suit the majority of hole-nesting birds in the area - blue, great and coal tits and possibly redstarts, though I have yet to see them in the area.

I’ve used Woodcrete-type boxes before and they’re widely used by biologists studying nesting birds. The front of the box is removable for easy cleaning, there are well-placed drainage holes in the base of box and they have a secure hook at the back for attachment.

Siting

All of the boxes were firmly fixed 2-4 metres up on the NNW to NNE face of birch, Scots pine or larch trees. There are few cats in the area and the partly-arboreal pine marten could reach them however high I placed them. I therefore chose positions that gave good flight lines for the birds, and reasonable sight lines for me to observe them without disturbing them.

The boxes will need annual cleaning and this is much easier if they’re not high above the ground.

The boxes are about 6kg in weight … another very practical justification not to place them too high.

Apparently the only way you know if there are too many boxes in an area is if a proportion are always unused. I’ve put up 10 in about 2 acres, with the option of increasing this if needed.

At the time of writing (late March) birds are establishing their territories. Some of the boxes were being irregularly visited, but it was too early for any to be occupied.

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