[Adam Cheeseman]

Hi Laura,

Apologies for the long response, but much of this info comes from some very respected names in the world of bats.

PART 1
Noctules will fly over floodlit areas in London exploiting chafers attracted to light, but they are generally flying above the light cone. I have watched lesser horsehoes take moths from a mercury vapour lamp, pipistrelles and serotines are known to do the same. Bat retinal structures vary across the species, which in turn, may affect their ability to cope with varying light intensity.

It is the Myotis and Plecotus species that we are particularly concerned about and I have given Dave the figures showing the decline of Daubenton's bat in our region (which will not be published until next year and bucks the national trend). I have seen a single Daubenton's bat habituate to monochromatic lighting below a certain level, but not to broad spectrum white lighting.I have never, ever found Natterer's bat in an area where there is lighting.

In short it is the type of lighting, it's luminous intensity, the location of the light spillage (onto river corridors etc) and diffuse range of light sources which may cause problems for bats, depending on the species.This is borne out by research, but the conclusions are usually: that bats avoid light to avoid their predators. This of course must play a part but the weakness is that it assumes that predators cannot see in the dark.

A contribution to the second part of your question, most of which you are probably aware : there has been guidance from government on mitigation for lighting over sensitive areas particularly AONB's. Alan Outen wrote this guidance and it was his case studies that appeared on the former DETR (Department of the Environment Transport and Regions) website.

Jenny Jones has written the guidance (English Nature 2000) applied to SSSI's and other statutory desinated sites.The Environment Agency use guidance of 'less <2lux spillage onto the water course'. Ealing Council website has some very sensible lighting guidance apropos the Clean Neighbourhoods Act. Google Rich and Loncore for details of the American Symposium on lighting now published and available on amazon.


PART 2
I would like briefly to comment on the correspondence below with a 'health warning' of my own.

Dave is of course right that the bats and lighting issue is unresolved and we need some convincing data - but in the meantime we don't and I would like to support the use of the precautionary principle by applying the best knowledge that we have access to at any one time - and Alison's recent London Naturalist paper is a very useful reference for this. Of course, even well-collected data from experimental studies can be overturned later by other studies that expose unforseen methological flaws or 'special case' scenarios. So, one might never choose to act until there have been several robust studies and a review paper with a meta-analysis of those to check that they really all do agree. Within the realms of ecological research, and the current rate of decline of some species, this could well be a long time after the metaphorical horse has bolted.

The effects of lighting are certainly not confined to their effects (real or imagined) on bats, and they may influence the behaviour/ecology of any other nocturnal animals (vertebrate or invertebrate), or indeed diurnal animals confused about when night actually begins or ends, or indeed the growth of plants. The perturbing effect of lighting on many night-flying insects (e.g. moths) is pretty easy to demonstrate and it is reasonable to suggest that being forced to divert course to fly around a light and being exposed to predation and additional energy costs as an alternative to finding a mate or feeding is likely to be a negative effect for those individuals involved. Repeat on a large scale and you get a larger scale effect that might affect species at a population level. For predators of those species there may well be an effect on prey distribution .... and so on.

Returning to bats - individuals or species that appear to be tolerant to lighting and feed on insects around lights may still be losing out. One must not make the mistake of assuming that just because an animal is feeding in a particular location it is 'happy' to do so - it may simply have no (or few) alternatives and is faced with either feeding there (perhaps with added risk of predation or added competition from other bats etc.) or suffering even greater energy losses by trying to feed on a depleted prey population in darkness where it is safer. This would be especially so if preferred prey species were drawn from the surrounding area into the lit area.

My health warning is therefore this, just because a species is observed exploiting a habitat or situation it does not mean that it is in a good state. Years ago my attention was drawn to the example of the Hawaiian goose - found confined to upland areas in which conservationists therefore actively conserved for them. However, disappointingly, the conserved populations were not sustainable, they required constant additions from captive breeding. Further studies revealed the geese to be birds of the lowland coastal areas, from which they had been displaced by human occupation. Once it was realised that they were in suboptimal habitat, their decline was easy to understand. Obviously this is a potted summary, and doubtless one can find flaws with the analogy - but hopefully it makes my point.


PART3
As a novice doing the Daubenton survey in Lewisham for the first time last year, I can only say that my bats were perfectly happy catching the insects that clustered around a lamp on a bridge over the stream. Very adaptable, our inner urban wildlife!


PART 4
Since 1995 there has been a NBMP (National Bat Monitoring Program) which is undertaken by volunteers with the data being analysed by statisticians. The NBMP has shown a substantial London decline in the Daubenton's bat, a Myotis species that requires dark river corridors, as most batworkers know.

We designate rivers as corridors for wildlife but it is a process of ‘designate and forget’. We never actively manage them as dark corridors for birds and mammal movement or retain any of the original vegetation in our new schemes which they or their insect prey find useful.

It is not necessarily the lighting per se which is affecting bat species but the sheer totality of lighting from a diffuse number of sources along with broad spectrum lighting which is replacing the monochromatic low pressure sodium lighting. During a recent survey, lighting on a footpath at Epping Forest SSSI measured 250 lux, , which is the same lux level as my living room. (No, I don’t live in a cave).

Some bat detectors now record lighting levels and many of us carry separate spot or logging light meters. The Environment Agency makes recommendations on the levels of light spillage onto water courses from bridge and pathway lighting.
[b]


PART 5
I'm firmly against light pollution, which has spoiled the tranquility of many of the larger open spaces in London, but I council caution over accepting the evidence of a direct effect of light pollution on bat numbers.

The issue is one of basic methodology. It's quite difficult to establish cause and effect in field ecology. There are two significant problems:

1. Many changes are over time, and all manner of other things also change over time. For example, it's unlikely that mobile phone masts have an adverse effect on bat numbers, but they will surely show a statistically significant correlation.

2. Other evidence comes from spatial comparisons - well lit sites with fewer bats than dark ones. Again, any two sites will differ in many other features, including those that could influence food availability for bats for example. There is also a risk here of selecting the evidence (often subconsciously through lack of interest in places that seem not to fit the preconception). Even in scientific papers there is a well-known "file drawer problem" whereby the uninteresting negative results are not so interesting to the journals.

The solution to these two problems is an experimental approach, but of course it's not easy to experiment with lighting and bat numbers. Long-term monitoring of bat numbers, however, could provide the accidental experiments that we need. By chance, some such monitoring sites will have lighting introduced, whereas others continue dark, and act as "control" sites for the "experimental" introduction of lighting. Of course a large number of monitoring sites is needed for this to be successful, and this is a good area for "citizen science".

The value of such an approach is illustrated by the very effective bird monitoring schemes run over many years by the BTO. The results have increasingly been used for accidental experimentation.

In my view we do not yet have confidence on the bat story, however convincing is the theoretical reasoning. We can apply the precautionary principle, but there's always a risk there of losing it when a good study comes along! It's time that our bat friends encouraged monitoring along the lines of the excellent BBS and does anyone know of published work that meets the requirements of experiment vs control as well as adequate replication?