Bat boxes

bat boxes at Coombe Country Park Bats have suffered a serious decline due to loss of habitat, timber treatment and pest control. To help ensure the future of the species you could put up some bat boxes.

These pages list only a few of the numerous designs available (including some prototypes) and concentrate on boxes most likely to be used by bats in the summer months.

all wooden boxes should be constructed from preservative-free wood

If you are making your own then use rough-sawn wood so that the bats can get a grip on the various surfaces. The boxes also need to be rainproof, draught free, and the wood should be no less than 25mm thick. They can be assembled using bat-friendly waterproof glue, screws or nails. A well-built box should last about 10 years.

To avoid damaging your trees when fixing the boxes, you can use headless nails or use a strap but then you will have replace the strap as the tree grows. Only stainless steel or aluminium nails should be used to attach boxes to trees as other types can poison the tree.

siting your bat box

plan view of 3 boxes on a tree positioning boxes on trees The boxes should be sited on trees and walls as high as possible (no lower than 2 metres) and clear of any overhanging branches so that the bats have direct and easy access to them. Avoid putting a box on a tree trunk where ivy is actively growing as this can quickly block the entrance. On buildings the boxes should be placed as near to the apex as possible as bats prefer to roost at the highest point. Ideally place the box on a wall where the late afternoon sun will warm it, such as a west or south-west facing wall. Only use a south facing wall if it is not in full sunlight all afternoon, to avoid overheating the bats (this is also true for bird boxes). Ideally you could put up several boxes facing different directions so that if one box gets too hot or cold for them the bats can move to another.

signs of use

Look for bat droppings or slight staining immediately below the exit hole or on the landing plate. The droppings look similar to mouse droppings but are dry and crumble to dust. The best way of assessing whether bats have moved in is to watch your boxes at dusk to see any bats leaving to feed and by looking for droppings or urine stains at the entrance.

Bats may use several different roost sites throughout the year and your boxes could only end up being used for a short time, if at all. However, bats are 'ancestral' in their use of roost sites and should return for roughly the same period in following years once they have chosen a site. Of course, the more bat-friendly your local area and garden is the more bats you are likely to attract to your boxes. To see how you can improve your environment see gardening.

bax boxes on treeOnce or twice a year, if it is practicable, give the slotted opening a brush to remove any build up of dust, dirt or cobwebs that could block the opening. Also prune back any plants or tree branches that may have grown across. The best time to do this work is when the bats have left for their winter hibernation, which is from about late autumn to early spring. In particular avoid the period between June to mid-August when female bats are normally giving birth and lactating.

The pictures below show a design which is proving very successful in attracting both Pipistrelles and larger bats including Barbastelles. It is quite large and has a number of vertical baffles to mimic tree trunk or branch splits.

PLEASE NOTE that these pictures show a box that can be opened for inspection but it is illegal to open a bat box if it is being used, unless you hold the appropriate licence from Natural England.

bat box with vertical bafflesbat box with baffles - side view

And here's some views of the inside showing the baffle arrangement.

bat box with lid openbat box from underneath

The plans to build the original, non-opening version of this bat box can be downloaded from the Vincent Wildlife Trust.

There are numerous designs for bat box 'kits' and on this page you'll find just a couple......
the 'finnemore' bat box

This bat box was designed by Mick Finnemore, one of the founder members of Warwickshire Bat Group. From our experience it is a very successful design, especially liked by Pipistrelles probably due to its slim internal dimensions. Because it has such a narrow internal space it avoids the problem of birds trying to nest inside it.

Finnemore batbox design

Download a pdf of this bat box design.

the pete maule 'wedge'

Pete Maule Wedge batbox

Download a pdf of this bat box design.

Bats and their roosts are protected by law meaning that as soon as any box is being used by bats, whether they are there or not, it is protected and both the bats and the box need to be left undisturbed. So unless you have an appropriate licence from Natural England you should not inspect bat boxes where bats are known to be roosting.
further reading

"An analysis of the usage of bat boxes in England, Wales and Ireland" by the Vincent Wildlife Trust (pdf, 1.4Mb) May 2006.