Bat Boxes
Making and Siting Bat Boxes in your Garden
By 'Sarah'

 

bat.gif (2402 bytes) Bats are some of Britain’s most fascinating mammals, yet sadly, their numbers are declining. Loss of habitat and a decline in food availability are probably the principle causes of their decreasing numbers, due to the effects of human activity. The felling of old trees, the in-filling of cavities in buildings and the stopping-up of caves and mine shafts have drastically reduced the availability of roosting sites for bats. Food shortage is a problem too, partly due to the widespread use of pesticides, which kill off many of the insects that form the bats’ diet, and also the destruction of insect habitat. Avoiding the use of pesticides in gardening can help provide the bats with food, and the correct construction and siting of batboxes can help to provide important roosting sites for Britain’s only winged mammals.
bat anim.gif (3918 bytes) We have seen bats flying over our garden at dusk every summer since we came to our present neighbourhood, eleven years ago. However, it has become evident that bat numbers are diminishing despite an apparent abundance of insect food; providing batboxes seemed a practical solution to redressing the loss of roosting sites. A lot of thought must go into the making and siting of batboxes. As bats do not like cold and wet roosting sites, boxes need to be damp-proof and draft-proof. They must be sited out of the reach of cats and in a reasonably quiet position.

Forest Stewardship Council

We decided to make two batboxes using the plans on a leaflet published by the RSPB. The wood used was a 2.5m plank of untreated larch, cut from wood approved by the Forestry Stewardship Council. It is important to use untreated wood as the bats might be put off by the smell of preservative, or even poisoned by it.

RSPB plan here! A new window will open.

Both boxes each had: a back plate (33cm x 15cm), two side pieces (each 15cm wide, with a short side of 14cm, and a longer side of 20cm joined by a diagonal), a front plate (14cm x 15cm), a lid (20cm x 15cm) and a base (9cm x 15cm), which partially covered the opening at the bottom, leaving a 15-20mm gap for the bats to enter and leave by.

These pieces were marked out using a T-square, then cut with a small handsaw. Each finished box had the following dimensions: 33cm high, 15cm wide, and 15cm deep.

The inner surface of every cut piece of smooth wood needed to be roughened to allow the bats to grip it. At first we used a wire brush, but this was not very effective so the teeth of a saw were used to finish the job.

RSPB Plan here! A new window will open.

Next a chisel and mallet were used to bore a groove on the back plate of the box, 5cm from the top, for the lid to rest on. To do this, the edges of the groove were defined with the chisel, 28mm apart and 3mm deep. Then slits, 2mm apart, were made in the wood between the two edges; the wood then flaked away easily when tapped with the chisel, to leave a neat groove.

Each lid was planed to allow it to fit flush with the backboard. A strip of wood (2cm wide) was then screwed to its front edge to keep it in place atop of the box. Each box was screwed together, using 1-inch wood screws. The finished boxes looked like bird boxes, except that the entrance slit was underneath instead of at the front.

 

A pyrography iron was used to name 'The Bat Shack'.

Just for fun, we then used a pyrography iron to burn names onto the boxes. Box 1 was called ‘Bat Corner’ and Box 2 ‘The Bat Shack’. All the nearby trees are within too easy a reach of cats, so the boxes were fixed on the side of the house, just below the level of the first floor windows. ‘Bat Corner’ faces southwest, and ‘The Bat Shack’ faces northwest, as bats like a choice of boxes that face in different directions, for use at different times of  the year.

 

'Bat Corner' The position of the bat boxes. 'The Bat Shack'

Figure 1. ‘Bat Corner’

Figure 2. The Position of the Boxes

Figure 3. ‘The Bat Shack’

 

Postscript

Three months after putting up the boxes, bats were noticed leaving the boxes at dusk. Since then, we have on several occasions glimpsed them emerging; when the weather turned colder the bats apparently vanished, suggesting that they are hibernating in the boxes. However, we cannot look directly into the boxes as this would disturb the bats, which is both illegal and cruel.

Some sources criticise batboxes in general, arguing that an isolated, ill-made batbox, which is leaky and draughty, will not be of any use in helping to protect these creatures. We feel that although this may be true, it is not a cause to dismiss batboxes altogether. If there are several well-made and well-sited batboxes, particularly in an area where there are inadequate roosting sites, bats may well take up residence.

So why did the bats chose to live in our batboxes? In the village where we live there are lots of trees, however, few of them are old and large enough for bats to live in. Our batboxes were carefully cut, planed, and put together, to ensure that they provided a snug haven from the elements. These things may provide the answer to this question.

It certainly seems that our batboxes have got the bats’ ‘stamp of approval’. Hopefully, it will prove to be a step forward in protecting our local bats.

 

 

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