Thursday, 14 February 2008

Armchair roost-searching

The holy grail of bat-work is finding roosts. Finding and watching feeding or commuting bats is great but the roost sites are the centre of the network of bat activity. More importantly, if we know where roosts are, we can ensure they are safe from disturbance or destruction.

So how do we find new roost sites? Basically, it involves one of three methods, though all three require a great deal of luck!

Method 1 is to seek out commuting bats and attempt to let them lead you to the roost. Great fun, and sometimes very successful, although hard work.

Method 2 is to simply stumble across one. Bat calls from worried householders can bring new roosts to light. Many bat-workers have had someone say casually "Bats? Oh there are hundreds of them in our attic - you should come and see them." A remarkable number of people have bats in their homes, are perfectly happy and don't make any fuss about it.

Method 3 is to carry out a dawn survey: bats tend to swarm around the entrance to their roost for 20-30 minutes just before dawn, so looking for them can be quite effective.

Whichever approach (or approaches) is used, some homework helps provide the best return for time and effort, and this is the ideal time of year to do it. We're lucky to live in an internet age and the web is stuffed with handy resources.

The NBN (National Biodiversity Network) Gateway houses a lot of records of roosting bats in Scotland, though it seems patchier south of the border. Go to, type a species name into the search box and then select the interactive distribution map. This is a handy (though slow) gadget which allows you to navigate your way around the records held. Unless you make special arrangements with data providers, you can only view the records at an accuracy of 100m, but that's a starting point for a roost search. Don't assume a record means that a site is known about. I recently found six local records of Brown Long-eared Bat roosts, which weren't know about in our local bat group. Remember also that an absence of records may mean a shortage of bat-workers, rather than a shortage of bats!

Maps are, of course essential for this sort of work. The Ordnance Survey have made their mapping available on-line, as an interactive tool. In my view nothing can ever replace a dog-eared 1:25 000 scale map, complete with coffee-stains and ten years-worth of pencil marks and scribbles, but I have to admit that the Get-a-map service is extremely convenient!

Some bat roosts are found in historical man-made structures: old buildings, bridges, mines, lime kilns etc. The Royal Commission on Ancient and Historical Monuments Scotland (quite a mouthful!) have an on-line database of archaeological site records called CANMORE, which can be searched either manually or via an interactive map. This is similar to the NBN Gateway, but faster. It's a terrific resource, which I've been using recently to search for potential hibernaculum sites, such as world war 2 pill-boxes, disused mineworkings etc. Go to and try a CANMORE search. Even if you don't find a potential roost, you'll be amazed what archeologists have found near where you live!

Once we have a site which may be of interest, what can be done next? Taking a close-up look from the air may help. Windows Live Search offers an interactive satellite photograph service, similar to the well-known Google Earth, but with significantly better coverage. Go to and try zooming in to the site of interest. If your site is in a high definition area, not only can you zoom in close and see what it looks like, you can also get a sense of the surroundings habitats, flyways, foraging potential and so on. It's also a damn good toy just to play with! (I know the photographs of York were taken on a Tuesday because my Mum has her washing on the line!)

Knowing my luck, summer will come along and I'll be too busy to follow up these sites, but at least I will have had a winter bat "fix" and being familiar with these resources often comes in handy with all sorts of fieldwork planning.

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