The felling of dead, old and hollow trees along with the advent of "Dutch Elm Disease" and the hurricane of 1987 in southern Britain, has considerably reduced the availability of natural roost sites for bats. Some modern building practises and the associated building regulations implemented during extensive development and building repairs have not helped either! Bat boxes provide artificial roosts sites for bats and are important for conservation and research. They cannot however, entirely replace or substitute for natural tree holes and crevices in buildings.
In the U.K. twelve bat species have roosted in bat boxes. Six of these (Pipistrelle, Noctule, Leisler's, Natterer's, Daubenton's, and Brown long-eared bats) are said to have produced babies in them. Bat boxes are also widely used as autumn mating roosts and by individuals and groups throughout the whole year.
In order to help the future of bats in your area, you may wish to put up some bat boxes and encourage others to do likewise.
It is however far more fun to make your own - or even design one of your own.
The second type is a thin box - of variable dimensions, made with a rot-resistant wood, which can be affixed near the top of a wall or near the ceiling of a damp underground tunnel or cellar. These have attracted species such as Pipistrelle, Brown Long-eared, Natterer's and Barbastelle in situations where there are suitable hibernation conditions, but a lack of crevices in which the bats can - and prefer, to hide. See also Bat Brix
Boxes must be rainproof and draught free, and made from a rough-sawn long-lasting timber such as Larch or Sweet Chestnut at least 25mm (one inch) thick. Assembly can be accomplished using screws, nails or waterproof glue. The lid can be snapped into a groove on the back plate or hinged and secured with wire or a hook and eye.
These materials make one box:
Only attempt this with adult supervision and take all reasonable health and safety precautions.
Cut timber by diagram - you should have 6 pieces. The back plate can be groved with saw-cuts to help the bats to crawl up into it. Assemble with the screws as in the diagram - pilot drill the holes first to stop the wood splitting. Check the access slit in the bottom is at least 15 mm and less than 20 mm before tightning the screws. Adjust if too wide or too narrow.
Nail 2 panel pins either side of the base plate to prevent it swiveling. Cut a piece of spline to secure the lid and use two screws to hold it. Another piece of spline is nailed inside the lid to act as a stop - to keep the lid tightly in place. A plastic, rubber or metal hinge to secure the lid could be used instead.
Make any adjustments needed to produce a rain-proof solid finished box as you proceed.
Your bat box is now finished and ready for occupation!
Where to put your bat box
Avoid damaging trees when fixing your boxes. You can use copper or aluminium nails or straps on commercially grown trees - steel nails or screws of an appropriate length, may be fine on trees that will not be harvested. Always obtain permission from the landowner!
Ideally bat boxes need to be sited in a south-facing direction on trees, but walls or posts at least 5 M (15 feet) high will also be used, but they must be clear of overhanging branches or wires making flying access easy for them.
Place boxes as high as possible in sheltered or wind- free areas exposed to the sun for several hours per day. It is often suggested that up to three boxes per tree is suitable for a project, but just singles can be used. Woodland rides and glades are ideal, particularly if situated close to a marsh or river valley.
Inspecting your bat box
Bats and their roosts are protected under the Wildlife and Countryside Act 1981, so it is an offence in the U.K. for members of the public to disturb, handle or kill bats.
The occupancy of boxes can be checked by watching at dusk during the summer, and by looking very carefully for the small black droppings underneath. It is also sometimes possible, on some designs, to check for bats from below, with a torch through the slit.
A licence should be obtained from English Nature (in the U.K.) and training undertaken, before any regular inspections, involving disturbance, are carried out. Even then, boxes should not be looked at during the months of June, July and August (in the U.K.) when bats are giving birth and lactating.
It may be some months or even years before boxes are regularly used. In some areas almost every good box can be used at some time during the year - in other places less that one in twenty boxes may be occupied. A good rule of thumb is that if your box has not been used within 5 years, try re-siting it.