How to attract bats to the garden

Posted by on April 23, 2016

Pru Baker recently contacted me regarding Bat boxes made by Dr. Roche. That prompted me to do a bit of  research which I would like to share with you.

Dr. Roche's bat box

Dr. Roche’s bat box

If  any of our  club members  are interested in a “bat box”Dr. Roche can be reached on 044 343 3004 for further information.  They are thin and fit easily under the eaves. Apparently bats are excellent mozzie eliminators and when he erected his, the bats moved in within a few days.

Article by Ken Thompson – The Telegraph

22 APRIL 2016 • 7:41PM

It’s not difficult to persuade birds to use nest boxes – heck, even I can do it. When it comes to bats, however, we are in different territory altogether. In his 2007 book Garden Natural History, Stefan Buczacki devotes one short paragraph to bats, observing effectively that no one knows anything about bats  in gardens.

Once again, the Conservation Evidence Project (conservationevidence.com) rides to the rescue – up to a point. Its new synopsis of what works – or doesn’t – in bat conservation brings together all the evidence it could find, not just on bat boxes but on other measures intended to benefit bats.

There is quite a lot on bat boxes, but let me start with two warnings. Not much has changed since Stefan Buczacki’s despairing comment: there has still been little scientific research on bat boxes in urban areas, and hardly any in gardens.

And second, even in the woodlands where bat boxes are usually tested, reported occupancy is often low. Partly this is because bats are just harder to keep track of than birds.

Birds tend to use a single nest box, but bats typically move around a group of roosts, using each for a different purpose – nursery colonies, bachelor pads, night roosts, mating roosts.

But first the good news. In the two studies that looked at trends over time, numbers of bats using boxes increased, so it looks like bat numbers may often be limited by the availability of roosts. There is also surprising unanimity about box location and colour. Boxes in sunny locations were more likely to be occupied than shady ones, and darker-coloured boxes (which absorbed more sunlight and got warmer) were used more than pale-coloured or white boxes.

It looks as if bats  or temperate ones anyway, like to be warm. Also, perhaps surprisingly, on the few occasions the comparison had been made, boxes on buildings tended to be used more than those on trees.

So, if your bat box is the right colour, and in the right place, does it matter what shape and size it is? Yes it does, but not in any simple way.

As the synopsis says, the 10 studies that looked at bat-box design produced “varying results”. To try to bring some order to the situation, let’s look at the most useful UK study, carried out in a woodland in Buckinghamshire.

This compared four woodcrete boxes made by Schwegler (2F, 2FN, 1FS, 1FF), which I won’t try to describe – you can find pictures and descriptions on the Schwegler website (schwegler-natur.de). They also used an “Apex” wooden box with a triangular top covered in tough, plastic mesh to allow the bats to grip onto it, and a slit entrance at the bottom, running across the back of the box.

The results were clear: the common brown long-eared bat, perhaps the second most likely bat to turn up in gardens (after thepipistrelles), strongly preferred the 1FS design, which is the largest of the Schwegler boxes, described by them as a “colony” box, providing “plenty of space for a large number of individuals to congregate”. Bats are sociable animals, so maybe this isn’t too surprising.

However, this result is complicated by the fact that, during the bird nesting season, birds rather liked the 1FS box too, and competition from birds at this time forced the bats to use their second favourite, the 2FN box. Very clear is that the wooden Apex box was never used at all.

Another UK study also found competition from birds for bat boxes, but showed that providing plenty of bird boxes reduced this competition.

A huge study of more than 3,000 boxes by the Vincent Wildlife Trust (vwt.org.uk) came to broadly similar conclusions. South-facing boxes were better than north-facing, and woodcrete better than wood. The bats encountered most often by far in its survey were pipistrelles, which is also the bat most likely to turn up in your garden. Conveniently, pipistrelles much preferred the Schwegler 2F “starter” box, recommended if you’re not sure whether there are bats in your area. If it’s not occupied after a number of years, it’s easily converted to a bird box by simply changing the front panel.

That is my final recommendation; buy a Schwegler 2F box, put it up somewhere sunny and settle down for a potentially long wait. Don’t panic if nothing happens at first – when it comes to bat boxes, patience is a great virtue.

All the evidence shows that boxes that have been up for a few years are far more likely to be used than recently installed ones. So give it four or five years before abandoning hope, but if there are still no customers, convert your box to a bird box, which is almost guaranteed to work, since birds prefer woodcrete too.

Ken Thompson is a plant biologist with a keen interest in the science of gardening. He writes and lectures extensively and has written five gardening books, including Compost and No Nettles Required. His most recent book is Where do Camels Belong? The Story and Science of Invasive Species.

 

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