Many bats both in the U.K. and many other parts of the world have suffered a tremendous population decline, due to roosting space losses, feeding habitat losses, various ‘pest’ control measures and timber treatment in buildings.
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.
The boxes should be large enough to allow a maternity colony to cluster to conserve heat to keep the babies warm. They may be used throughout the year except during periods of very cold temperatures. How to make your own Bat Box.
The BIGGER box
The BIGGER box – such as Cambs bat group have now errected a few of these slate covered monsters…. Our BIG box some 3 feet high by 2 or so wide. This photo is of the one at Santon Downham (Forestry Com.) 7 Pips there yesterday. There is another in regular use at Ranworth Broad on the side of a house.
Some boxes have been designed that open at the sides, front or base and allow inspection with less disturbance, but may be more complicated to make.
Bat Conservation Trust Approved
In the U.K. the Royal Society for the Protection of Birds sell a Bat Conservation Trust approved bat box which you need to assemble, as it comes flat-packed.
It is however far more fun to make your own – or even design one of your own.
Bat boxes made from cement and woodchips are available. They are black coloured, last much longer than timber ones, are more attractive to bats and resist gnawing by Grey squirrels, but are difficult to make, or quite expensive to purchase.
This is a picture of Natterers bats in an open-bottomed timber slot (pre-hibernation). These are also used by Brown Long-eared Bats.
Two types of hibernation boxes can be provided. The first are the outdoor ones which need fixing to trees or buildings in sheltered locations. They need to provide insulation from cold winter temperatures. They have been made from hollowed out logs or 100mm (4-inch) thick timber or with layers of plywood interspersed with insulating material. These have been insufficiently tested in the U.K. to evaluate their full potential.
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
An excellent booklet that covers the subject in detail is “Bat Boxes” by R E Stebbings and S T Walsh. It is available fromBat Groups of Britain.
Home-made bat boxes are usually made with ‘soft wood’. No timber preservatives should be used, because these may be harmful to bats, although a dark coloured stain or thin coat of emulsion paint can help to warm a box placed in sunlight. Untreated boxes will last up to ten years.
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.
Materials to build a Standard U.K. Bat Box
Tools: Saw, hammer, screwdriver, pencil and tape measure.
These materials make one box:
- Plank of 6 inch (150 mm) by 1 inch (25 mm) 1.2 m. long timber (Larch recomended)
- 1 foot of approx. 25 mm x 20 mm spline
- 13 x 45 mm Bright zinc screws
- 4 x 40 mm panel pinsOnly 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.
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!
Site boxes in areas where bats are known to fly. This may be an urban park, an existing nature reserve – or your own back garden. Areas with few natural roost sites (such as commercial conifer plantations) can be good.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.
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.
Open carefully because bats may be hanging on the top. When a box has been inspected, bats should be removed before the top is replaced, to prevent trapping the bats’ feet. The bats should be placed near the entrance and allowed to crawl into the box. Releasing them by encouraging them to fly in daylight may attract predators such as Sparrow Hawks – be warned!