Giving bats a home

Once in a while you meet someone who takes your understanding of a subject forward in leaps and bounds. Last week, it was the turn of bats.

The revelation came from a conversation I had with Matt Dodds, a leading light in the bat world in the Midlands. And he was able to share with me some emerging results from in-depth studies of the roost and nest sites of bats.

The advice that is normally meted out is to have a range of boxes at different aspects, for example putting three boxes in a ring around a tree. And, unlike birds, the advice normally says to include a box on the south side as bats need the warmth that birds would find unbearable.

But studies are now showing something rather different. What bats appear to prefer are:

• Boxes to be in shade. This is perhaps the most important element.
• Boxes don't need to have a southerly aspect. Maybe a lone male Pipistrelle will use it, but it is much too warm for most, especially for groups of females rearing the pups.
• Boxes should be as large as possible - bats like to feel they are a long distance from the entrance, and the interior climate will be much more stable.
• Nor do boxes need to be at great height - they can be fine a couple of metres off the ground, although they still need a good flight path in..

It means that boxes such as these above are probably very unlikely to be successful.

It has also been shown that traditional methods of counting bats emerging from boxes using bat detectors underestimate totals, often considerably. New, expensive thermal imaging technology is showing that large roosts can hold dozens of bats.

Bat boxes will still only provide a home for a small number of species; trees, caves and buildings (if they can access the lofts and cavity walls) will still provide most of their homes. But for me, the new advice is still very relevant as I am just planning where to put bat boxes in my new garden.

Of course bats still have their other Home Needs if they are to find a home, plentiful small insects being the key. Having a chemical-free, plant-rich garden complete with large pond, shrubberies and tall trees should do the trick. In combination with the box advice, I will have every chance of successfully giving some of my local bats a better home.