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Bats & Bat Boxes

A Wildlife Tip Sheet™ from Jacobi Jayne & Company

by ecologist Andrew McLeish

It often surprises people to hear that there 16 species of bat in Great Britain. They represent between one quarter and one third of all the British mammal species and yet are probably the least well known.

The use of bat boxes to attract bats was first tried in the early part of the 20th Century in Europe and Russia. Today hundreds of thousands of boxes are erected every year and they vary enormously in size and design.

Bats are social animals and often congregate in very large numbers. The largest colonies in Great Britain number several thousand bats but in other climates millions of bats can be found in a single cave.

What type of box ?

It is important to provide the type of box which is likely to be used by bats in your area. A few species of bat, like the Pipistrelle and the Brown long-eared are found throughout the British Isles. Fortunately, both of these species like to use bat boxes so wherever you are as long as you site your box correctly you should have a good chance of attracting bats.

A basic wooden bat box can be constructed from rough sawn timber. A bat box of this sort looks very much like a tit box but instead of a hole at the front it has a narrow slit of up to 1.5 cm in width on the underside of the box. This slit allows access to bats but not to birds.

Schwegler 'woodcrete' bat boxes offer considerable advantages over normal wooden boxes. Firstly, they have excellent thermal insulation properties. Many bats like to live in a stable temperature, warm or cool depending on the time of year. Wooden boxes fluctuate in temperature a great deal and conditions inside the box can quickly become unsuitable for bats.

'Woodcrete' boxes are also extremely long lasting, do not rot and are predator proof. Bats can return to the same roost year after year so the advantages of having a bat box which will still be there in 20 years' time are obvious.

Choosing the right Schwegler Bat Box

There are seven different types of 'woodcrete' bat box. Each one has been designed to encourage particular species, to use at a particular time of year or in a particular environment.

2F Bat Box. This is one of the simplest designs. It is a free hanging box with a narrow entrance slit on the front. The box is hung either from a branch close to the trunk of the tree or is fixed to the trunk with the supplied aluminium nail. It is a general purpose bat box attractive to the smaller British bats. Diameter 16cm. Height 33cm.

2F Bat Box with double front panel. Externally similar to the 2F, it has a roughened wooden panel inside the box which simulates a crevice. This box is particularly favoured by Daubenton's bat and Nathusius' pipistrelle. Diameter 16cm. Height 33cm.

2FN Special. A larger box with both a wide access slit at the base and an access hole on the underside. Whilst attractive to many species it has been particularly successful in attracting Noctule and Bechstein's bats. May be free hung or fixed to the trunk. Diameter 16cm. Height 36cm.

1FF. A recent design which is rectangular in shape rather than round making it suitable for attaching to the sides of buildings or in sites favoured by bats such as bridges. May also be used on trees. It has a narrow crevice-like internal space which is preferred by many different species. Has been particularly successful in attracting Pipistrelle and Noctule bats. Width 27cm. Height 43cm. Access slit 12-24mm.

1FW Hibernation Box. A monster of a box! Weighing 27kg this box is designed to provide a protected environment for bats throughout the year but particularly through the cold winter months when bats hibernate. The box can be sited outside or in places used by bats (e.g., caves, converted pill boxes). Comes complete with special fixing brackets and has three internal wooden panels imitating crevices. It is important to fit this box very securely if mounting above ground and away from areas used by the public. Diameter 38cm. Height 50cm.

1FS Bat Box. A small and lighter (10kg) version of the 1FW with lower insulation properties. Diameter 28cm. Height 44cm.

Type 27 Bat Box. A box designed to be built into brick walls. This box is particularly useful for incorporating into new buildings to attract bats or when renovating existing buildings with bats and there is a desire to provide new roost sites. The box should be cemented into the wall. Contains a single internal wooden panel The removable front panel allows for easy cleaning. Width 18cm. Height 29cm. Depth 23.5cm.

Where to site your box. Your box is much more likely to be used if it is sited near to somewhere where there is a source of food. Bats feed over gardens, fields, water and in woodlands. Find a tall mature tree in your garden and fix the box at a height of 4 metres above the ground with the access facing south west or south east. If you do not have a tree of 4 metres in height you can place it lower but you are less likely to attract some species such as the Noctule. You can also put a box on the side of your house. If you do this, try and put it somewhere which is not too exposed so it will not experience extremes of heat and cold.

If you are providing bat boxes in woodlands or other natural habitats place them where you have easy access for checking them from time to time. Often, good results can be obtained by putting a number of boxes in one area. For example, you can site 6 boxes over a 20 by 20 metre square with each box facing a slightly different aspect. Again, avoid siting boxes in areas which are very exposed, in frost pockets or where there is a chance of vandalism.

Once you start siting boxes at a height of 5 or 6 metres or even higher your chances increase of attracting Noctule bats.

Bats can discover bat boxes within hours of being put up. They may start using boxes as overnight roosts within weeks. However, it can be some time before a box is used regularly or as a breeding roost. If there appears to be no use of the box within the first two years then it would be wise to try re-locating it.

How do I know when bats are using the box? Once there is a roost in the box it will become obvious when they come streaming out at dusk to feed. The box might hold up to 50 individual bats. However, a lot of boxes are used by a smaller number of bats and unless you check inside the box you may never know if it is being used. Once the box has been up for a few weeks or months open it to look for bats or bat droppings. Bat droppings are very much like mouse droppings except that they crumble in your hand. Mouse droppings are very hard and do not crumble. If you find bats inside the box put the cover back on very carefully and then do not disturb it again. (Once you have found bats in a box you should not disturb them again unless you have a licence to do so.)

Maintenance of the bat box. Sometimes birds may successfully occupy a bat box. Do not disturb the birds whilst they are nesting. Once they are finished you can open the box and clear the old nest out. Sometimes bat droppings can build up in a bat box and it might be necessary to clean it. The 1FF and 2FN boxes are self cleaning as the droppings can fall out of the bottom.

How else can I attract bats? Bats need two things in life: somewhere suitable to roost and somewhere good to feed. Bats in Britain feed exclusively on insects and you can attract more insects to your garden in many ways. For example, you can build a garden pond or grow scented plants which attract insects. The Bat Conservation Trust publishes a leaflet Bats in Gardens which gives further information on suitable plants.

Andrew McLeish

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