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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.

The Biologist guide to British bats

Common and widespread

Brown long-eared bat (Plecotus auritus)

Long-eared bats are known as 'whispering bats' because their echolocation is so quiet. They have very sensitive low frequency hearing and often locate prey from the sounds made by an insect's movements.

Common pipistrelle (Pipistrellus pipistrellus)

Pipistrelles are the most common British bats. They mainly roost in buildings and trees, and feed over water, marshes, woodland, farmland, along hedgerows, in suburban gardens and urban areas.

Daubenton's bat (Myotis daubentonii)

Daubenton's bats look like small hovercraft as they fly over water, and can even be seen taking insects from the water's surface with their feet or tail. They roost in trees, tunnels, bridges and, occasionally, buildings.

Soprano pipistrelle (Pipistrellus pygmaeus)

The 'new' pipistrelle species was separated from the common pipistrelle in the 1990s. It is distinguished by its higher frequency call and pale facial skin. It roosts in larger colonies than the common pipistrelle.

Uncommon but widespread

Brandt's bat (Myotis brandtii)

Whiskered and Brandt's bats were only separated as distinct species in 1970. Brandt's bats mainly roost in buildings and trees, and feed in woodland, often near water.

Nathurius' pipistrelle (Pipistrellus nathusii)

Until 1997 this bat was known only as a migrant, but there are now a few breeding colonies in England and Northern Ireland. In Europe they roost in trees, but in Britain they roost in buildings.

Natterer's bat (Myotis nattereri)

This bat's broad wings enable it to fly slowly and prey on a variety of insects. They roost in old buildings, large-timbered barns and tree holes, and feed in open woodland, parkland, hedgerows and along waterside vegetation.

Noctule (Nyctalus noctula)

The second largest British species and usually the first to appear in the evening, the noctule has long narrow wings and flies in a straight line, very high and fast. They roost in trees, usually in woodpecker holes or rot holes.

Whiskered bat (Myotis mystacinus)

Whiskered and Brandt's bats are very similar species with shaggy fur, but the whiskered bat is slightly smaller than the Brandt's. They roost mainly in buildings and trees, and feed along woodland edges and hedgerows.

Rare

Barbastelle (Barbastella barbastellus)

A very distinctive bat with a pug-like face and large, wide ears that are joined together at the forehead. Only found in southern and central England and Wales.

Bechstein's bat (Myotis bechsteinii)

A woodland specialist, which roosts in tree holes, rarely in buildings, and feeds in woodland, from high in the canopy to near the ground. Found only in south east Wales and parts of southern England.

Greater horseshoe bat (Rhinolophus ferrumequinum)

The horseshoe bats can be distinguished from other British bats by their horseshoe-shaped noseleaf, which is related to their particular type of echolocation system. Found in south west England and south Wales.

Greater mouse-eared bat (Myotis myotis)

The mouse-eared bat was declared extinct in Britain in 1990. However, a single individual has been found hibernating in the south of England since 2002. There are no known summer roosts in Britain at present.

Grey long-eared bat (Plecotus austriacus)

This bat is similar in appearance to the brown long-eared bat, but is a little larger and greyer with a dark face. They roost in older buildings, barns, churches and trees. They are very rare, found only in southern England.

Leisler's bat (Nyctalus leisleri)

Similar to the noctule but smaller and with longer fur. They roost in tree holes and buildings, and feed over woodland, parkland and suburban areas. Rare, but locally common (up to southern Scotland), particularly in Ireland.

Lesser horseshoe bat (Rhinolophus hipposideros)

You can tell the two horseshoe species apart by the position of their wings at rest: the lesser horseshoe bat wraps its wings around its whole body, while the greater horseshoe bat's face can usually be seen.

Serotine bat (Eptesicus serotinus)

One of our largest bats, the serotine has broad wings and a leisurely flapping flight. They feed over pasture, parkland, woodland, tall hedgerows and gardens. Found mainly in southern England and south Wales.

Unknown

Alcathoe bat (Myotis alcathoe)

This new species, very similar in appearance to whiskered and Brandt's bats, was first described in 2001 in Greece. In 2009, they were recorded in Sussex and Yorkshire, but distribution across the UK is unknown.

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.

References

1) Mitchell-Jones, A. J. et al. The growth and development of bat conservation in Britain. Mammal Review 23, 139–148 (1993).

2) Walsh, A. L. & Harris, S. Foraging habitat preferences of vespertilionid bats in Britain. Journal of Applied Ecology 33, 508–518 (1996).

3) Barlow, K. E. et al. Citizen science reveals trends in bat populations: the National Bat Monitoring Programme in Great Britain. Biological Conservation 182, 14–26 (2015).

4) POST Note Number 476. Environmental Citizen Science. The Parliamentary Office of Science and Technology. www.parliament.uk/business/publications/research/ briefing-papers/POST-PN-476/environmental-citizen-science (2014).

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