Caped crusaders

Each summer an army of volunteers monitors UK bat numbers and, according to Dr Kate Barlow, their recent findings are good news

The Biologist 62(3) p16-19

At sunset on a warm, dry summer's day, hundreds of dedicated people are interested in more than just the view. Some sit in their gardens, carefully watching small gaps in the roofs of their houses. Others wander around towns and the countryside, through streets, fields and lanes, clutching beeping electronic devices. These amazing volunteers are all taking part in the Bat Conservation Trust's National Bat Monitoring Programme.

Since the programme was established in 1996, the Bat Conservation Trust (www.bats.org.uk) has been working with partners and volunteers gathering data on how our bat populations are faring. There are 18 species of bat in the UK, making up about a third of our mammal species. Many of our bat populations suffered considerable declines in the second half of the 20th century, driven by factors such as habitat loss through agricultural intensification and direct loss of bats from the effects of pesticides such as those used for timber treatment in buildings.

There is, however, a lack of quantitative evidence from this period that makes it difficult to determine the full extent of those declines. Then, during the 1980s and 1990s, there was an increase in interest in bat conservation in Britain, at least in part promoted by new legislation providing legal protection for bats from the Wildlife and Countryside Act 1981[1]. This resulted in improvements to the available information on distribution of bat species and locations of bat roosts, but there was still no clear picture of whether bat populations were continuing to decline, were relatively stable or were increasing in numbers.

One of the key problems is that bats are hard to monitor: they are small, nocturnal, often tricky to find and it can be difficult to identify species as they flit past in the dark. Survey methods commonly used include counts of bats in summer and winter roosts, capture surveys and, more recently following the development of bat detectors, acoustic surveys.

There is a general consensus among bat conservationists, both locally and globally, that monitoring bat populations is invaluable. This is not only to ensure their effective conservation and to determine how bats are responding to the unprecedented rates of environmental change, but also to provide a broader indication of the health of our ecosystems. However, there are still no standardised protocols for monitoring bats across countries or continents. In the 1990s, from work investigating habitat use by bats in the UK, researchers demonstrated that volunteers could be coordinated successfully to carry out bat surveys at a national level[1,2]. This work, and the increasing need to be able to report on the status of bat populations, led to the establishment of the National Bat Monitoring Programme, supported by government funding.

Our programme relies on volunteers to take part in different surveys throughout the year, including summer counts of bats emerging from maternity roosts, winter counts of bats in underground sites such as caves and mines that they use for hibernation, and summer bat detector surveys looking at activity levels of bats in different habitats.

Recently, we published our results, analysing data on 11 bat species collected by over 3,500 volunteers at more than 3,200 sites across the UK for a 16-year period from 1997 to 2012[3]. They show a generally favourable picture for the bat species that we monitor: a stable or increasing trend was found for all species over the period of the study from at least one survey type. This suggests bat populations are showing signs of recovery, almost certainly helped by the increasing public awareness of bats and interest in bat conservation in recent decades, combined with the legal protection for these species at a national and European level.

We must not become too complacent, though. While these are positive results, the current increases we are seeing in bat populations are likely to be only a small start in their recovery from previous losses. There is still much work to do, first to unravel the main factors driving the changes and second to expand our monitoring right across the range of bat species we have in the UK: some of our rarer species that are habitat specialists are not included in our monitoring programme as yet, as they are difficult to monitor or are rarely encountered. The National Bat Monitoring Programme therefore mainly shows us what is happening to the more common and widespread bat species and may not completely reflect all of the pressures and impacts on our bats.

What is exciting to me, though, is the success of our citizen science approach to bat monitoring. There has been criticism of citizen science projects and widespread concerns about the quality of the data. However, as the number of peer-reviewed publications emanating from citizen science programmes increases, the value of the data is becoming more widely appreciated, as was recognised last year by the Government in a parliamentary POST Note[4].

Our study has demonstrated how, through providing a structure and training for anyone who wants to get involved in bat monitoring, data collected by volunteers using standardised, multiple survey methods can be used to provide statistically robust population indices for a large proportion of our bat species at a national scale.

Our bat monitoring trends not only help us understand how bats are faring and shape our conservation work, but the data also contributes to EU Habitats Directive reporting and provides one of the 26 UK biodiversity indicators used to assess the UK's progress towards its biodiversity targets. We wouldn't be in a position to provide those key facts without the commitment and enthusiasm of all our volunteers. People power really does make a difference.

To find out more about the National Bat Monitoring Programme (NBMP), visit www.bats.org.uk/nbmp. The NBMP is run by Bat Conservation Trust, in partnership with the Joint Nature Conservation Committee, and supported and steered by Natural England, Natural Resources Wales, Northern Ireland Environment Agency and Scottish Natural Heritage. The NBMP is indebted to all volunteers who contribute data to the programme.

Dr Kate Barlow is head of monitoring at the National Bat Monitoring Programme and joined Bat Conservation Trust in 2008. After becoming hooked on bats during undergraduate expeditions to South America, she completed a PhD on the ecological differences between common and soprano pipistrelles.