Tuesday, 11 February 2014

"I know there aren't any bats..."

In my work I meet many bat roost owners, varying in attitude towards "their" bats from delighted to appalled and all points in between. I also encounter many people who are commissioning a bat survey because they have been obliged to do so. Often in the UK this occurs when someone applies to their local authority for planning consent to carry out work on a building. The law requires the local authority to consider protected species, so if there is any possibility for a bat roost to be present a bat survey must be carried out. "I know there aren't any bats there, but we have to have a survey" is often the client's opening gambit. It's not an unreasonable attitude: what little most people know about bats leads them to expect them to be highly visible, extremely rare and likely to roost in caves or gothic castles. Against that background it seems insane for a local authority to request a bat survey of a three bedroom suburban house, a 1970's primary school or a city centre council flat. Yet I and my colleagues frequently come across bat roosts in buildings like these.

This modern primary school is home to 280 Soprano Pipistrelles. They roost alongside the main entrance and most people think the noise is made by nesting birds.

Part of the problem is one of perception - bats are rare, that's why they're protected. Yet some bat species are very common. Here in central Scotland Soprano and Common Pipistrelles and Daubenton's Bats are all common, but have the same level of protection as rarities such as Whiskered Bats or Nathusius' Pipistrelles. Rarity isn't the sole reason for protection - vulnerability is a key issue. Our commonest species (in central Scotland), the Soprano Pipistrelle gather in their hundreds and even thousands to breed. The destruction of one of these roosts could harm the species over a large area. Bats reproduce very slowly - a single female will often only have one offspring in a good year and the need to gain weight swiftly in order to survive hibernation means that many do not survive. Thus bats are usually slow to recover from set-backs. Reducing prey availability caused by pesticides, illegal roost destruction through prejudice and stupidity and a host of other factors all combine to make legal protection essential.

Another factor in the misconception is the expectation that bats are visible in their roosts. We have Hollywood to thank for that. People expect to glance inside an attic and see a host of bats hanging from the ceiling, with their wings wrapped around their bodies. In the case of Horseshoe Bats that genuinely is the case, though bats tend to be a great deal smaller than they appear to be when in flight. Most other bat species in the UK roost in holes or crevices of one type or another, meaning that when they roost in buildings they are less likely to be visible to the uninitiated. Not long ago I surveyed a farm, the owner of which insisted there were no bats around his farm. Not only were there three species of bats roosting in his farm, there was a colony of about 80 Common Pipistrelles roosting alongside his bedroom window.

This colony of Brown Long-eared Bats are tucked into a crevice between two roof beams. If disturbed they tend to move deeper into the crevice, out of sight.

I'm not sure where the popular conception that bats only roost in old buildings comes from. It's certainly true that large country mansions and castles usually do contain bat roosts, but this often has as much to do with the presence of undisturbed spaces and the maturity of surrounding habitat as anything else. Modern house builders are surprisingly good at including loose-fitting fascia boards, poorly attached flashing and many other features which bats find to their liking and it is usually in modern buildings that people are particularly surprised to find bats.

Not a building which fits with the popular vision of a building used by roosting bats, but 800 Soprano Pipistrelles roost under the slates of this house every summer.

I have no doubt that there are many buildings around the country containing bat roosts that the owners are unaware of. Either they don't notice the signs or don't recognise them for what they are. Two years ago I spent a couple of weeks flying (when I'm not working with bats I fly gliders) from an airfield in Leicestershire. The club house there is a single-storey, L-shaped building about five years old. In the shelter of the L-shape are comfy tables and chairs, accessible from the bar. It's a nice place to sit on a summer evening and is well-used by club members. I had only been there a couple of days when I realised that a colony of Common Pipistrelles were roosting  at the wall-head alongside these tables. Each evening as the sun started to go down around ten bats would emerge and fly through the group of people who were sitting drinking and chatting. Nobody ever noticed them! I suspect people occasionally glimpsed a bat and assumed it was a songbird. The club management were entirely unaware of the presence of a bat roost in their recently-build clubhouse. If they applied for planning permission to change it and were asked for a bat survey I expect they would be astonished and annoyed at being asked to commission a bat survey...

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