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British bats: What's happening to their habitat?

Updated Tuesday 11th September 2012

Bat expert John Altringham discusses his fascination with bats and the implications of habitat destruction

In this extended interview from Saving Species, Professor John Altringham from the University of Leeds gives an introduction to the life, habitat and territory of bats—and the effect of road construction.


Bat flying Creative commons image Icon Veins In The Membrane / Taro Taylor / CC BY-NC 2.0 under Creative-Commons license A bat spreads its wings Copyright open university



Interviewer:  Well I’m now joined by John Altringham who’s a Professor of Animal Ecology and Conservation at the University of Leeds, and he’s involved in research on the effects of roads on bat populations, and indeed a great deal else to do with bats.  John, first of all, you’d better explain the fascination of British bats and in fact bats from all around the world.

Professor John Altringham:  The fascination for me is just two things: one the sheer diversity, you know, 1,200 species and growing; and their amazing biology, ecology, physiology.  The only echolocators, the only flying mammals, there’s just so much that’s fascinating about them. 

Interviewer:  And am I right in thinking almost one in three species of mammal is a bat isn’t it in the world?

Professor John Altringham:  It’s about one in four.

Interviewer:  Is it, oh right.

Professor John Altringham:  Yes.

Interviewer:  But it’s still a huge amount.

Professor John Altringham:  But numbers fluctuate, it changes.

Interviewer:  How does that compare with the UK, we’ve got a pretty impoverished bat fauna compared with say tropical areas?

Professor John Altringham:  Well, we have got an impoverished bat fauna, but again as a proportion of the total number of mammal species they’re up there at a quarter to a fifth.

Interviewer:  Many people, they see bats flitting about, they don’t really understand them a great deal.  You know, they’re things that flit by in the night if we’re lucky.  Some people who aren’t naturalists are a little bit worried about them, even frightened of them indeed.  There’s a mysteriousness still attached to bats even in the 21st Century.

Professor John Altringham:  I think there is, and I think it’s just because in many respects they are so difficult to observe and to study.  You’ve got to be a bit of a fool to try and understand the ecology of these things.  All these late nights and working in the dark, you’re chasing a small highly mobile elusive animal.

Interviewer:  And when you see bats in the hand it’s then you realise just how small they are, some of them are remarkably small.  I was looking at Bechstein’s bats recently and again, you know, you read about them being medium sized bats; they’re not, they’re tiny.

Professor John Altringham:  That’s it: it’s a medium sized bat that is a quarter the weight of a mouse.

Interviewer:  So when it comes to conservation of bats in the UK, what do you think are the most pressing issues?

Professor John Altringham:  The pressing issues, I don’t think they vary much from those of other animals.  It’s habitat destruction, habitat degradation, fragmentation; what really is accounting for the loss of biodiversity in many other areas, and bats are very much the same.  I think one of the big things about bats is they may be very small animals but they have delusions of grandeur; they think they’re very much bigger.  And so they have, they operate over very large areas of the landscape and they reproduce very slowly and live for a very long time.  So you get a big crash in the bat population and it doesn’t recover in the way a rodent population could do, it takes very much longer.

Interviewer:  And the habitats that bats like, they are remarkably specific some of the species aren’t they?

Professor John Altringham:  All bats love water and they love woodland, to varying degrees.  The rarer species are very much tied to those habitats, but all species like water and woodland.  They’re the two things that we’ve probably lost most of in the last century.

Interviewer:  And obviously bats require different roosts at different times of year.  Many of them use special maternity roosts for bringing up young, and they’ll use winter roosts for hibernation as well.  Again this makes conservation of them a little bit more complex.

Professor John Altringham:  That’s right, because you can’t simply protect what they need at one time of the year if you’re not looking after what they need at other times.  So you’ve got to look at them in the round, across the very large landscape and across all the seasons.

Interviewer:  When I think about bats, I often think about people being nervous about moving them out of their houses because they know that bats are highly protected.  I mean would it be fair to say that bats are pretty well served when it comes to legal protection in the UK?

Professor John Altringham:  I think they’re extremely well served when it comes to legal protection; I think there are issues about how effective that protection then is in practical terms.

Interviewer:  What do we have to do?  I mean for example if we find bats in a house or we find a tree roost with bats in, what are our legal obligations as citizens?

Professor John Altringham:  As citizens do nothing at all.  Obviously if there’s a conflict of interest in some way, if there are bats in your roof and you want to do a loft conversation, then that needs to be discussed.  It doesn’t exclude the bats, it means, it doesn’t stop the work; it just means it has to be done in the right kind of way.  But if you’re not doing anything then all you need to do is let somebody know that you do have bats to help put the bats on the map, and then leave them to it because they cause no damage.  They’re of no concern really to the average householder.

Interviewer:  Now we’ve talked generally about conservation and our duties towards bats, but I know recently you’ve been involved in research on the effects of roads, particularly road building on bat populations, so give me some idea of the evidence that you’ve got for the way roads and traffic affect British bats.

Professor John Altringham:  In essence the evidence is that as you walk away from a road with a bat detector and record the number of species and the overall activity of bats, they just rise and rise and rise to something like threefold what they were at the roadside by the time you’re 1,600 metres away - this is the M6 and the M5.  We suspect there are probably effects of other major roads.  To establish the result obviously we looked at the most extreme case and looked at a motorway.

Interviewer:  And what’s actually happening, how are the bats’ lives being impacted by this road?

Professor John Altringham:  I think it’s lots of way.  I think light and noise and mortality on the road itself are factors, but the fact that it’s operating over 1,600 metres suggests it’s probably acting on bat demographics.  You build a road that cuts a bat’s habitat in half say, so that it’s excluded from foraging in half of its home range, the bat has two choices: it moves away from the road and the colony re-establishes somewhere more distant; or the bats have to run the gauntlet of the road.  Either way you’re likely to get a reduction in bat populations close to the road.

Interviewer:  And you mentioned earlier on that bats have delusions of grandeur when it comes to their size compared with the sort of habitat they need, so this division of territories, is it crunching bats together or is it just simply reducing the overall numbers of bats, or reducing their territory size?

Professor John Altringham:  I think it starts by obviously reducing territory size.  This may cause displacement and in fact there is evidence it causes a reduction in reproductive success if the bats stay next to the road.  If the bats move they’re obviously then in competition with another colony.  We assume that the landscape is pretty much at carrying capacity, so if bats are forced to move into the territory of another colony then they’re competing for food and overall you would expect a loss in population size again.

Interviewer:  What about direct collisions?  We know bats are equipped with wonderful ultrasound, which enables them to detect objects coming towards them, that presumably doesn’t apply to fast moving traffic?

Professor John Altringham:  That’s it: they didn’t evolve alongside cars; they evolved to pick up, to look at stationery landscape and small moving insects.  And so even if they pick up a car, the car is moving much too quickly and they have no evolutionary response to it.  And even if they tried to get out of the way of course even a fast bat is flying at 20km, maybe 25km an hour, that’s not going to get it away from traffic.

Interviewer:  Now I've never seen a bat in a gutter, I wouldn’t know if I’d hit a bat or whatever, are they common as road casualties?  I mean if what you’re saying is true mortality of bats must be huge across the whole country?

Professor John Altringham:  It’s potentially very large, and certainly for the stretches of road that have been looked at, particularly in Europe and North America where most of the work has been done, if you extrapolate those numbers up to the entire road network then yes it’s very large numbers of bats are being killed.

Interviewer:  When I hear about species being killed on roads, I think of barn owls and toads and badgers, so how widely recognised is this a problem for bats?  Are we just taking enough notice of it?

Professor John Altringham:  I think we’re only just beginning to wake up to the issue of roads.

Interviewer:  What are we doing about it?  Is anybody making any efforts to make roads slightly more passable for bats?

Professor John Altringham:  People are trying to make roads more permeable and more safe by taking bats under roads or taking them over the road but over the road at a height which takes them above the traffic.  But the evidence we’ve got so far is that it’s very mixed success.

Interviewer:  Just explain to me John, how do you take a bat over a road?  You’re giving them guidelines are you?

Professor John Altringham:  You’re giving them guidelines.  What you’re trying to do is where there used to be a hedge that they followed you’re now placing pylons at either side of the road and stretching wires with balls or discs on them, and so the idea is that the bat sees these as a surrogate hedge.  My belief is that the hedges fulfil many more requirements than a simple echolocation guide, and the bats simply don’t really acknowledge their existence.

Interviewer:  So the theory behind these bat bridges or gantries is that bats will follow existing hedge lines and they’ll cross the road at a safe height.  How effective are they according to your studies?

Professor John Altringham:  Very ineffective, we’re not protecting more than maybe a few percent of the bats at most.  It’s hard to be even sure that they’re doing any good at all. 

Interviewer:  Well bats have been seen around these gantries haven’t they?  They’ve been observed around them.  Does that mean that they’re being used or that they’re effective?

Professor John Altringham:  We put a definition of if the bat flies within two or five metres then we would make an assumption it was using it, and on that criterion we still only found something like 2%, 5%, 9%, depending on the gantry, were flying close enough to the gantry to suggest it was being used.  All the rest were flying, crossing the road at some other point and crossing the road unsafely, they were flying at traffic height.

Interviewer:  Now quite a few people are advocating gantries aren’t they, professional ecologists for example, they’re being used in new road constructions to a small extent -

Professor John Altringham:  That’s right.

Interviewer:  - and there are others planned, they must believe that these work.

Professor John Altringham:  Well I’m sure they do believe they work, I think the problem is that there is this distinction between use and effectiveness.  They need to know that they protect a large percentage of the population otherwise they’re ineffective.  Basically they’re not collecting the evidence to support their effectiveness, and that was a gap that we identified and therefore set out to fill.  And I think that’s what we need more of.  When we build structures, whatever these structures are for mitigation, we need to test them, we need to be very objective in saying have we got the evidence that they actually work?

Interviewer:  Well they’re relatively new aren’t they these bat gantries, so is it a case of giving them a bit more time?

Professor John Altringham:  Well one of the gantries we looked at has been there nine years, and it’s on an existing commuting route, and after nine years the bats have not adjusted to it; they still cross the road at an unsafe height.

Interviewer:  So you’re an academic with a special interest in bats, what do you think would make roads more bat friendly?

Professor John Altringham:  It’s a tricky, I think the thing we need to do, underpasses are one.  I think underpasses have the potential to do a better job because the bats feel more secure going under the road.  Green bridges, much wider bridges with vegetation on top of them, which connect the landscape more effectively also have potential.  We could, because what we’re doing is dividing habitat up, we could simply when we take a piece of territory out by building a road, we could just improve the habitat on either side of the road to try and compensate for that.

Interviewer:  Now all this is research isn’t it, and we could plan the routes I suppose as well to help bats cope a little bit more with the road passing through their territory.  This is all going to cost money, is it more expensive than the gantries?

Professor John Altringham:  I do suspect that one of the reasons gantries are used is because they’re a relatively inexpensive option.  But to put that into perspective, if the money spent on an average gantry was used in study, in research, we would have had the answer as to whether or not they worked a long time ago.  So it’s all relative.  Everything costs money but I think research is actually one of the cheaper things, and in the long run it could save us a lot of money. 

Interviewer:  John Altringham, thank you very much.


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