The Isles of Scilly Bat Group

A brief history...


Knowledge of bats in Scilly up to 2006.

In the last two decades of the twentieth century, it had been feared that bats, once so common, might be disappearing from Scilly. In the first decade of the twenty-first, that is not the case and there is some evidence that their numbers may now be on the increase. Scilly has few mammals and it would be very unfortunate if these lovely animals were no longer with us.

Of the 1,300 species of bats in the world, only 17 are found breeding in the UK and for only one, the common pipistrelle, was there reliable evidence for permanent residence in Scilly. There had been some tantalizing suggestions that there might have been other species present here, but the hard evidence was scanty and remained to be confirmed. The possibility remained that such sightings might have been of temporary migrants.

Workers at the Bird Observatory on St Agnes in the 1950s and 60s had recorded seeing Pipistrelles and Long-eared bats (possibly the much rarer Grey Long Eared Bat) but had not noted numbers or other details. From Tresco Abbey, there were stories of mesh screens being put over windows at night to prevent bat entry and sacks-full of bat droppings being removed from a barn! Rosemary Parslow’s 1988 report (1) had speculated that loss of roost sites through barn conversions was an important contributory factor. However, another report, from the 1980s, of a bat found dead from lindane poisoning suggested that the decline had complex causation. Lindane was used in the bulb industry but its use has now been banned. Whatever the causes, the decline was clearly a cause of concern and Rosemary Parlow’s report (1) warned of a possible trend to extinction. Carol Williams and other members of the Cornwall Bat Group had conducted research on the Islands during the 1990s. Their 1997 report (2) found that the bat population was certainly vulnerable but that measures such as ensuring that there were continuing surveys on all the inhabited islands and that someone should be trained to deal with queries about bats and to promote bat conservation could help reverse the downward trend. English Nature produced a species Action Plan in 2004 (3) that essentially formalized what was in Carol’s report.

The first detailed observations on the bats of St Mary’s were made by David Mawer, Senior Conservation Warden with the Isles of Scilly Wildlife Trust. David recalls that bats had been a regular feature at Porthlow when he was a child but his real interest had begun when he spent a year in New Zealand, when he was able to acquire skills in trapping and radio tracking. On his return to the Isles in 1997, he noticed that there was little bat activity. When he acquired a bat detector, he confirmed their scarcity, although not complete absence. He began collecting information – some recorded, some anecdotal.

By 1998 David was walking regular transects with a bat detector, carefully recording any bat passes and much other information including: time, location and weather conditions but was encountering few bats. An important advance, originating from his stay in New Zealand, was to couple a voice-activated tape recorder to a detector to create an automatic bat detector, allowing the recorder to listen to a full night’s bat activity at a single location in just a few minutes. With support from the Wildlife Trust he undertook an intensive week of training with bat experts on the mainland and obtained a special bat handling licence. Membership of the BCT followed with participation in the National Bat Monitoring Programme.

After a few years observing little activity, things began to change. Bats emerging at dusk from a St Mary’s maternal roost increased from 1 to 7, to 38, to 60, to 98 between 1998 and 2005 and, from a roost on Tresco, from 40 to over 100. Other observers, too, including bird-watchers, began noticing a general increase in activity. As an example of how valuable a detector can be, David describes the identification of a bat as a pipistrelle with the detector, when an observer without a detector was quite convinced that the animal was “too large to be a pip”. David found that virtually all records were of pipistrelles; however a noctule was once recorded by the automatic equipment, demonstrating that migrations do occur. Bat activity recorded on several uninhabited islands suggested regular inter-island bat movements. David’s records can be consulted at the Wildlife Trust.

It was clear that much needed to be learned about the social habits of Island bats, especially the locations of their various roosts. Females congregate during the summer in ‘maternal roosts’ and one such, at Maypole, needed to be studied in detail. Little is known about the location of male roosts or where the animals hibernate in winter. A major roost can be found at Tresco Abbey. Bats are also observed on St Agnes, Bryher (where a small roost is known) and St Martins. Whether they are ‘permanent residents’, or visitors from St Mary’s and Tresco, remained to be established.

The foundation of the Bat Group.

That was the situation in late 2006, when the Bat Group was formed. The inaugural meeting was held in December 2006 with 15 people present. This has stimulated more general interest in bats on the Islands and increased the number of people with an interest in and a capability of studying Island bats in more detail. Three members have become licensed bats wardens and are consequently able to play an important part in helping to conserve bat roosts and discourage developments that will lead to a repeat of the decline seen at the end of the twentieth century.

The detailed progress of the Group since its inauguration in 2006 can most conveniently be followed by consulting the annual reports. Briefly, the highlights can be summarized as follows.

Public engagement.

An important aim of the Bat Group in aiding bat conservation has been to engage with and educate the public about bats. In particular, people have needed reassurance that bats are not harmful, do not get entangled in one’s hair and are, when you get to know them, delightful little creatures. The knowledge that each bat needs to consume thousands of small insects per night goes some way to convincing us of their services to mankind! Regular interviews on Radio Scilly by members of the Group have helped in this objective. The work of the licenced bat workers has been particularly effective. It involves visits to private homes and business premises to ascertain whether bats are present, when a application for building work that might affect bats, if present, has been made. The opportunity has always been taken to discuss with applicants why the survey is needed and to provide them with useful information about bats. Over the years, the bat workers have been encouraged by the general interest shown in bats, improving attitudes towards them and high levels of cooperation. 

Our programme of bat walks, held monthly between April and September, has also been a pleasurable and effective means of public engagement. These walks have been popular among visitors, who have expressed great appreciation of the events and their greater knowledge about bats. Several members of the Group have also organized activities, including bat walks and making bat boxes, for local school children. Finally, the Group’s meetings have been widely advertised and those that have attended have contributed some excellent discussion and gained greatly from the experience.

Bat recording and research.

The Group has been committed to developing a programme of research to discover where bats roost, where they feed and how their numbers and behavior have been changing over time. Members have been encouraged to report bat sightings and to take part in more formal long-term projects. Chief among these has been participation in the Bat Conservation Trust’s (BCT) National Bat Monitoring Programme (NBMP), which covers the whole UK. Two aspects of this are followed in Scilly: regular counts (twice in June, twice in July) of bats emerging from a specified maternal roost (‘Roost Counts’) and also observations of bat passes as we walk around a specified circuit with a bat detector (‘Field Surveys’). One roost count site, at Maypole Farm, St Mary’s, has been studied regularly since 1999 and another, at Tresco Abbey, has been studied more intermittently. Since 2013, mainland members Lotty and Lyn Packman and Ian Barr have enabled us to make many more observations (including those for the NBMP) on Tresco during their summer holidays there. Data from these surveys are sent to BCT, which coordinates national records and publishes trends in bat numbers and activity all over the country. Details of the NBMP surveys in Scilly can be found in the Annual Reports of the Isles of Scilly Bat Group.

Several small surveys have been done by members (sometimes in collaboration with visitors) using automatic detector/recorders (‘Anabat’, ‘Songmeter’), which can be left at a specific location for various periods of time. These instruments can be programmed to record sonic calls from bat passes on to a memory card. The information can be analysed using specialist software to display a sound profile (frequency vs time) and the date and time of the recording. Such analyses provide information on bat activity and allow species identification. One such project picked up a noctule, a Nathusius’ pipistrelle and a soprano pipistrelle as well as the usual common pipistrelles, which dominate the bat population here. The most detailed information on bat activity in Scilly to date was obtained in the summer of 2011, when 10 bats were tagged with miniature radio transmitters and then their movements tracked each day for two weeks with radio receivers tuned to a different frequency for each bat. These studies indicated how far bats travelled each night, the locations of their feeding grounds and revealed that they often relocated to different roosts for short periods before returning to the point at which they were trapped. The Group is grateful to Dr Fiona Mathews and colleagues at the University of Exeter and members of the Avon and Wiltshire Bat Groups for providing the expertise for trapping and tagging bats and locating the signals and also to the IOS AONB for grants to purchase the transmitters. The results of the study were presented as an MSc Thesis to the University of Exeter by Katie Goodman (4). An exciting find of this study was that one of the tagged bats was a pregnant brown long-eared bat. Attempts to follow up this species have been unsuccessful so far, as their low intensity sonic calls cannot be picked up on our detectors.


From its foundation in 2006, the Group has held several meetings each year, starting with one in March to plan its programme, followed by others on topics such as the making, siting and yearly inspection of bat boxes, the use of detectors and discussions on the results of surveys and projects. The twenty or so bat boxes on St Mary’s have generally been inspected in October. Few have been found to be occupied but a small programme of renewal of old boxes continues and several householders have been supplied with a box for their premises. In 2010, we started what have now become yearly visits by a member of BCT staff, who talks about some aspect of the work of BCT or about general aspects of bat biology. Originally, the group had an in formal affiliation with BCT but in 2012, following an extensive reorganization of BCT’s relationship with Bat Groups, a Partnership Agreement was adopted and signed. This has given the Group access to the considerable educational resources of BCT.

Between 2007 and 2013, an AGM was held in November or December to review the year, elect officers, present accounts and discuss ideas for future work. The last formal AGM was held in November 2013. It was then agreed to cease the practice on the grounds that very few members were ever able to attend. It was proposed that there should be one main meeting per year on some aspect of bat studies, which would incorporate a brief business meeting that would cover some aspects previously included in the AGM. As this meeting would take place in the summer but the financial year did not end until 31 October, it was agreed that the Treasurer would prepare the accounts, have them audited and send them out to all members with an invitation for them to direct questions to her if they wished.

This system has been in place since 2014, when the main meeting was on the topic of bat detection and sound analysis. A full report can be found in the Annual Report for 2014.

In the years since the founding of the Group, members have attended meetings on the mainland, which have not only been educational but have served to advertise the existence and activities of the IOS Group. In 2008, the secretary and treasurer attended the BCT Annual Conference at Reading University and presented a short account of the formation and activities of the Group. In 2013, they attended BCT’s South-West Region meeting at Exeter University, attended workshops on ‘sound analysis’ and ‘bats in trees’ and presented a short paper on the apparent discovery of soprano pipistrelles on Bryher but not on other Islands. A full account can be found in the report Sopranos on Bryher. There are some published studies on the differences in habitat preferred by common and soprano pipistrelles (5,6) but these do not satisfactorily account for why soprano pipistrelles should prefer Bryher. The solution of this mystery will no doubt occupy some members for years to come!

Grants and other income.

The Group was fortunate in obtaining several grants in its formative years. In 2009, a small grant from the NHS provided for the purchase of reflective jackets, used mainly during bat walks but also by volunteer bat workers in survey work. Grants for the IOS AONB’s Sustainability Development Fund (SDF) in 2009, 2011 and 2012 enabled the purchase of small bat detectors (used on bat walks and by members to make routine observations) and automatic detecting/recording equipment (‘Anabat’ and ‘Songmeter’) for more structured research projects. An endoscope for looking for the presence of bats in boxes, trees and in building structures, night vision glasses, a web-camera and a Roland recorder to attach to small bat detectors have also be purchased on SDF grants, for which the Group is most appreciative. The increasing need to seek grant aid caused us to amend our original very informal ‘Aims and Objectives’ document into a more formal Constitution in 2011 (see Constitution) as recommended by BCT.




  1. Parslow, R. (1988). Bats on the Isles of Scilly. Report for the Bat Groups of Britain Support Fund.
  2. Williams, C. (1997). Bats of the Isles of Scilly. Report for the Cornwall Bat Group.
  3. Clitherow, J. & Mc Dougall, A. (2003). Species Action Plan for Bats on the Isles of Scilly. English Nature, Truro, Cornwall.
  4. Goodman, K. Species diversity, roost sites and habitat use of bats on the Isles of Scilly: implications for conservation. MSc thesis, University of Exeter, 2011.
  5. Davidson-Watts, I, Walls, S & Jones, G. Differential habitat selection by Pipistrellus pipistrellus and Pipistrellus pygmaeus identifies distinct conservation needs for cryptic species of echolocating bats. Biological Conservation, 133, 118-127, 2006.
  6. Nicholls, B & Racey, P. Habitat selection as a mechanism of resource partitioning in two cryptic bat species Pipistrellus pipistrellus and Pipistrellus pygmaeus. Ecography, 29, 697-708, 2006.