The method used to attach the box to the tree should keep the nestbox rock steady and safe from falling. Several methods are used, and they're described here.

Single back bar

Probably the most often used, this form of attachment has the advantage of simplicity. A plank of wood 3-4 in wide fixed to the back of the box is nailed or screwed to the tree trunk. The plank should be thicker than the wood used for the box (say 3/4 inch) and extends above and below the box. The upper extension should be longer as it takes most of the strain, and should therefore have more screws put through it (at least three, as shown in the photo) than the lower extension. This form of attachment is not suitable for roping or wiring. (Illustration from photo by John Baker)

Disadvantages: prone to side-to-side rocking, e.g. in a strong wind. To minimise this the horizontal pairs of screws or nails should be placed as far apart as possible. A further problem arises here in that on a narrow trunk screws placed away from the centre line may not go far enough into the tree trunk to be secure.

Double back bars or battens

A method I came up with to get round the problem of rocking by having two lines of contact with the tree trunk. The battens are placed about 4 inches apart. Suitable for roping or wiring.

Disadvantages: extra carpentry. A camber on the battens is recommended to give a better fit to the curvature of the trunk, and to find the best angle of camber for the tree may require a scale diagram based on the trunk diameter. (More on this on Page 7 in Section 11.)

Direct screwing or nailing through back panel

As shown here with this chimney box, this method is not recommended as the side screws or nails are going to go through a lot of air before they bite wood. A simple way to get round this would be to place the outer screws closer together. The attachment is then essentially the same as the single back bar method above.

In one well-known owl cam box the nestbox is screwed through the back panel from the interior of the box. This has obvious aesthetic advantages (no fixing bars needed) but requires a large entrance opening if it's to be done easily.

Disadvantages: as for single back bar. A further problem is that the 9-mm ply in the example on the right could lose its integrity with age, weakening the attachment.

Platform mounting

An intriguing method illustrated here with a nestbox from Devon. This is a method for placing the box between two branches. The advantage of this method is that it provides a fixture that's completely steady in high winds and is also probably quite easy to set up.

Disadvantages: only suitable for low-profile boxes like the one shown. Might get a little fussy in the detail. For example one needs access through the box to be able to screw it down onto the platform, and the supports might be too far apart, requiring cross-supports.

Cross bars

Another suggestion of my own, this is another method for fixing a box between two branches. Suitable for screwing (or nailing) and roping.

Disadvantages: can be fiddly! The branches have to offer four points that all lie in the same vertical plane or padding will be required. Worth considering but not recommended unless the type of position shown in the photo is the only option.

Roping and wiring

Attachments using cord and wire have two advantages: they don't damage the tree, and no screws or nails have to be removed to undo the fixture. On the other hand they may need extra fitments on the box, like eyebolts (below), to make the attachment. I've tried two types of cord: nylon and polyester. Nylon tends to come in white only, but it's more flexible and longer lasting than polyester. Polyester is slightly stiff and slippery and so knots attempt to unravel themselves. As nylon doesn't have these problems I much prefer it. Wind the cord more than once around the tree trunk or branch to get a completely secure (non-slipping) attachment, as shown in the pics below. Knot ends can be secured with garden wire.

Double back battens with roping

The method used on our main nestbox. Rather complicated to engineer, but it's proved to be an excellent and totally reliable fixing. I used this method because the tree is not our property and must not be damaged. Note also the polyester suspension cord. This goes through a ring tied to a branch above and is used to haul the box up. It's left in place for extra security.

Disadvantages: time-consuming carpentry and bolt-fixing; can also take longer than other methods to set up in the tree.

Wire is often suggested as the means of attachment for chimney boxes when they are slung at an angle under a branch. As I've not used wire (and probably never will) I can't really comment.

A hybrid method: metal band with screw holes

Available from the Wheatear accessories page, the MP07 Band Pack is a 5-m length of galvanised metal with 5-mm holes along its length. 1-in screws are used to attach the band to the box and 2-in screws to attach the band to the tree. The £3.99 pack includes screws and washers. (Wheatear sells one of the few letterbox nestboxes with reasonable dimensions for tawnies -- see Page 9: Commercial box review.)

Comment: This looks an interesting and possibly convenient attachment, but its long-term security depends entirely on how long the galvanisation stands up to the weather. Once that goes and the band starts to rust, catastrophic failure is on the cards. Regular inspection at close quarters would be essential, especially after a year or two in place.

There's more on single and double battens on Page 7 in Step 11: Tree-fixing battens.

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