Bat Brick

THE NORFOLK BAT BRICK

A BRIEF DESCRIPTION AND GUIDE TO A BAT CONSERVATION AID

The Bats 

There are sixteen resident species of bat in Britain of which thirteen have been found in East Anglia in recent years. Of these, six species prefer damp undisturbed underground (or at least semi-underground) sites in which to hibernate, for at least part of the winter.

A protective grill positioned over a bat cave

 Hibernation

All British Bats have to hibernate during the winter months when there are no flying insects for them to feed upon. Species like Daubenton will start to sleep from about mid-September until mid-March or later, depending on the prevailing weather conditions. To achieve this sound sleep enabling survival until the spring they typically require:

 Darkness, with little or no disturbance

 High humidity – over 90% for most species

Suitable Structures

Many kinds of underground or semi-underground sites may be used by bats, including natural caves, cellars, ice-houses, brick and lime kilns, disused railway tunnels, old army buildings and a whole range of natural and man-made tunnels of many different kinds.

 A steady temperature, above freezing, but below ten degrees C. with a gradient, or range of temperatures

 Freedom from potential predators

 Crevices to hide in (that’s where our Norfolk Bat Bricks fit in!)

Why “Bat Bricks”?

During research on hibernating bats in East Anglia during the 1980s it was observed that some underground sites seemed environmentally suitable, but lacked cracks and crevices conducive to hibernating bats. The installation of some experimentally designed brick crevices in two sites during the autumn of 1984 quickly produced results. Development has continued in order to find the best combination of materials and aperture size.

A Norfolk Bat Brick with single Daubenton hibernating inside

 Suggested Placement Points

 Installation

These bricks would typically be used to replace an existing perhaps crumbling brick in a brick-built vaulted tunnel. The old brick should be carefully removed using a grinder, drill or cold chisel, taking proper safety precautions, then inserting the bat brick using an appropriate mortar (e.g. a soft lime mortar for old brickwork, or 6:1 sand:cement for modern brickwork). Modern resin-based mortars can be used, but they should be used sparingly, only in the summer when no bats are present, with extra ventilation and so placed to provide a water soluble ‘wick’ with the original substrate. Prop the brick in place with a length of timber or an “Acro-prop” for a day or so until set, then carefully point-up around any gaps.

They are NOT ‘entry bricks’, neither were they designed to be used facing into the cavity wall of modern houses and are considered unlikely to be used by bats in this situation.

 What is a Norfolk Bat Brick?

These are brick-sized objects approximately 200mm x 100mm x 70mm hand-made from an absorbent clay, roughened with sand and fired to about 1100 degrees C. to make them frost-proof. They have a series of slits of the correct size for Daubenton’s, Natterer’s, Brown Long-eared, Brandts, Whiskered and Barbastelle to hide in.

These are of a registered design and are onlyproduced by The Norfolk Bat Group.

 

 Alternative Fixings

In existing concrete tunnels or sites where it is considered difficult or undesirable to excavate or damage the existing surfaces, then surface attachment is acceptable, though may not give quite such good results. Embedding the bricks into the concrete roof of a new tunnel also works well. Simply place the bat brick on the surface of the shuttering ply, having first filled all the holes with sharp sand or grit, allowing a little to spill out when placed. This stops wet concrete entering the holes and gives a rough gripping area around each bat brick after the shuttering is removed. Do seek the advice of a structural engineer before doing this, as these units may influence the structural integrity of a cast concrete tunnel roof.

How Many?

In East Anglia our largest hibernation sites contain perhaps 400 bats at peak. However at most sites one typically finds less than a dozen bats of two species. Since only 10% of bats, from a given population, are seen at any one time, each of these small sites could be ‘home’ to over 120 bats!

1 – 3 bats per bat brick have been seen in most occupied sites during December – February, since the first experimental ones were installed, but occasionally up to seven bats of three species will occupy a single Norfolk Bat Brick. Obviously they are going to work best where there are plenty of bats, but a shortage of suitable hibernating holes. Over 3000 of these items have now been placed in the UK, with considerable success.

Our experience is that our most densely occupied underground hibernating sites have less than one sleeping bat per 3 cubic meters of air space, so something the size of say a World War II air-raid shelter with about 30 cubic meters of air-space might need no more than ten bricks set in a variety of locations.
Cost and Delivery

There has been a heavy demand for these bat bricks, but they are now available again. The price is currently £10.50 each (with discounts for quantity) plus transport at cost (please phone or fax for quote – or arrange your own transport). They weigh c. 2.5 kg each, so cost just over £1 to post, but can be sent by carrier at cost. Delivery times for small quantities are typically within 21 days, when in stock. Please allow 12 weeks for larger quantities and also note that drying and firing times may be further extended during the winter months.

 Ordering

Please fax your order to: 01508 550850 – or telephone 01508 550784 to discuss your requirements. You may also post your order to: The Norfolk Bat Group, The Barn Cottage, Wheelers Lane, Seething, Norwich, Norfolk. NR15 1EJ. Invoices will be sent to recognised firms and bat groups, on the understanding that payment will be within 30 days, but small orders should ideally contain a cheque for an agreed amount.

INFORMATION CORRECT AS OF APRIL 2015.