Bird Box Installation AcrossSurrey And Kent:Fitted Properly While We're Already Up There

Hole size is the single biggest factor in which species will use a box. A 25mm entrance suits blue tits and excludes larger competitors; 28mm opens the box to great tits as well; 32mm is sized for house sparrows, which nest in small loose colonies and often prefer boxes grouped a short distance apart rather than isolated. Robins and wrens will not use a hole-fronted box at all, they need an open-fronted design, sited lower and better hidden in cover such as ivy or a dense hedge line rather than in the open canopy.

Across gardens in Oxted, Caterham and Godstone, a mix of hole sizes on mature trees plus one or two open-fronted boxes tucked into hedging usually gives the widest range of species a reasonable chance. We talk through what is already visiting the garden before recommending a mix, since there is little point putting up a sparrow terrace where sparrows are never seen.

The general rule is 2 to 4 metres up, facing between north and east, so the box avoids the strongest afternoon sun and the worst of the prevailing rain from the south-west. A slight forward tilt helps rain run off the roof rather than in through the hole. Where possible, a clear flight line to the entrance, not screened by dense twigs right in front of the hole, makes it easier for adults to approach quickly, which matters once chicks are being fed.

Spacing matters for territorial species: blue tits and great tits will defend a nesting territory and do better with boxes spread around a garden rather than clustered on one tree, while house sparrows are the exception and are often happy with several boxes close together. Getting this right at the planning stage avoids boxes competing with each other for the same birds.

Nails and screws driven directly into a trunk or branch create a wound the tree has to compartmentalise, and as the wood grows in girth each year, a rigid fixing becomes buried, sometimes only two or three years later. That buried metal is a genuine hazard for anyone using a chainsaw on that tree in future, and it is one of the reasons we avoid nails entirely.

Instead, boxes are fixed with wide webbing straps or wooden battens that allow the branch to keep expanding without girdling, and that can be loosened or repositioned as the tree grows. It takes slightly longer to fit than a couple of nails, but it protects both the tree and whoever works on it next, including us, on a future visit.

Under the Wildlife and Countryside Act 1981, it is an offence to intentionally damage, destroy or take a wild bird's nest while it is in use or being built, or to disturb the birds while nesting. The practical nesting season runs from roughly March to August, though it can start earlier in a mild year, so any tree work or box fitting within that window means checking for active nests first. If a nest is found, the work is delayed until the birds have fledged.

This is one reason autumn and winter are the best time to fit new boxes, it gives them a full season to weather in and lose any strong scent of new timber before birds start prospecting for nest sites the following spring, and it avoids any risk of disturbing an active nest elsewhere in the same tree while fitting.

A well-made box in a reasonably sheltered position typically lasts several years before the timber needs replacing, but it needs an annual clean-out regardless of how sound it looks. Old nesting material harbours parasites that can put off the next occupants or harm chicks in a following brood, so each box should be opened and cleared in autumn, once the nesting season has fully finished and any young have fledged.

While cleaning, it is worth checking the fixing has not started to bind against the growing branch, that the roof still sheds water properly, and that the entrance hole has not been enlarged by a squirrel or woodpecker looking for an easy meal. A box that fails on any of those points is better replaced than patched, and if we are already doing other work in your trees, replacing a tired box costs very little extra.