Conservation assessments have recently been published for many species of wildlife on the Isle of Man, including an outline for Manx species of bat (Manx Wildlife Trust). It is generally assumed that bats, like so much of our wildlife, declined considerably in the second half of the 20th Century, confirmed partially by the recollections of the older members of natural history societies that bats are not seen nowadays in the quantities that they once were.
While there are no quantitative assessments of the population levels of our various species even today, some support is given to this view by Wagstaffe’s (1975) recollections of seeing 20 to 30 clusters of bats in a church tower near Douglas. One cluster was caught and counted, amounting to 700 Natterer’s bats, a number of Whiskered bats and a few long-eared bats. In 1988 it was reported that three barrow-loads of bats were removed from a church having been gassed some 20 years earlier (Stebbings 1988). From the volume of dead bodies an estimate suggests between 12,000 and 15,000 bats were killed, presumably in the proportions of those same three species counted by Wagstaffe.
Bats have a slow reproductive rate with only one pup per year per adult female, one reason why they were given protection in the UK in 1980, where other threats were felt to be accidental destruction of breeding roosts, inadvertent poisoning by woodworm treatment chemicals and loss of feeding habitat consequent on the widespread changes taking place in the countryside. Again, it is assumed that similar factors were at play in the Isle of Man but some considerations, not least the apparent relatively recent appearance of three species of bat, suggest that might be an over-simplification.
There are currently NINE known species of bat inhabiting the Isle of Man. Most of these are probably of long-standing, if only relatively recently confirmed, but two, perhaps three, species are thought to have colonised the island since 1950 (indicated by a star* below) while one cryptic species was only separated, across Europe, by DNA analysis in 1992.
| A timeline of bat identifications in the Isle of Man | |||
| Late 19th Century | Mid-20th Century | Late 20th Century | 21st Century |
| Brown long-eared bat – (Bride) | Natterer’s Bat – (Ballaugh) | Leisler’s bat*- (Michael) | Nathusius’ pipistrelle* – (Malew) |
| Common bat (=common pipistrelle) | Whiskered bat – (Braddan ) | Soprano Pipistrelle (cryptic species – split from common pip) | Lesser Horseshoe Bat* – (Rushen) |
| Daubenton’s bat (Calf of Man) | Daubenton’s bat – (Braddan & Patrick) | ||
All our species are said to be associated with woodland which was sparse a hundred years ago. Most of these species also live in houses and other buildings, the number of which has also increased by at least 30% over the same period. Bat habitat and habitations would therefore seem to have increased over the last 100 years perhaps counter-acting to some extent the factors reportedly causing a decline.
Bats, and their roosts, have been protected in the Isle of Man since the 1990 Wildlife Act but unfortunately there are no baseline data on population levels from that time on which to judge the success or otherwise of the legislation. It is possible, however, to undertake comparisons in activity levels with sites in the UK using an online app developed by the Mammal Society. Twenty-seven survey sites have been analysed using the Ecobat system, ranging from the Chasms to the Ayres and these results help to inform an assessment of the status of the populations of the various species of bats recorded.
On protected sites (nature reserves, ASSIs and wildlife sites), and on some farms, bat species diversity and activity levels compare very favourably with selected UK sites and score highly in the comparative assessments. It is probably safe to assume that bats in the Isle of Man are now doing at least as well as those in the UK, where a recent assessment by the UK Bat Conservation Trust (BCT) found that three species had increased their population since 1999 while four species were stable. Two more of our species, recent colonists, now have widespread distributions in the Island.
| B CT National (UK) Monitoring Programme: results to date for species also found in IoM | ||
| Increased since 1999 | Stable since 1999 | Insufficient data |
| Lesser horseshoe, Natterer’s, common pipistrelle | Daubenton’s, whiskered, brown long-eared, soprano pipistrelle | Leisler’s, Nathusius’ pipistrelle |
There are still threats however facing Manx bats. Roosts are lost every year to house improvements and re-roofing projects, despite attempts at mitigation. More energy efficient houses may also be less favourable to bats in the future while the new style breathable roof membranes are known to pose a direct threat to bats by entangling them in the finely spun fibres of which they are made. The BCT also estimate that some 250,000 bats are killed annually in the UK by cats. On an area for area basis that would equate to over 500 bats in the Isle of Man, killed each year by cats.
Bats are recognised as indicator species and can tell us much about the health of their, and our, ecosystems. Every effort must be made to continue to monitor our bats and attempt to assess possible changes in population and, for example, Biodiversity Action Plans have recently been drawn up for the lesser horseshoe bat and the three species of Myotis bats.
The Manx Bat Group now has data from over 730 surveys of one night’s duration, or longer, on which to base an assessment of the fortunes of our bat species.
Common Pipistrelle Pipistrellus pipistrellus
A ubiquitous species, recorded during 94% of all surveys, all over the Island and from sea level to over 400 m altitude. It can be encountered in towns, over beaches, in degraded or pristine habitats and while it is not possible to give an estimate of numbers, activity levels at surveyed sites can be assessed from the number of recordings made during acoustic surveys. Nine per cent of 744 acoustic surveys recording common pipistrelle show then being present once per minute on average, all through the night, throughout the survey, be it of one or several nights’ duration. There are a further 14 surveys with common pipistrelles recorded more frequently and, at one location, up to seven times per minute.
Counting bats emerging from their maternity roosts is another way of estimating numbers, or at least keeping track of trends in population levels. Unfortunately, common pipistrelles have a habit of switching roosts rather frequently, even when they have dependent young, and the Bat Group knows of one modern estate on the outskirts of Douglas where five of the 70 or so houses have bats at some time or other during the summer. Nevertheless, of the 150 or so active, or assumed to still be active, maternity roosts known to the Bat Group nearly half are likely to be of this species (53 identified to species level, 15 classed as pipistrelle genus). These range in size from 10s and 20s to 200 or so in one or two cases.
The Ecobat results show that out of 119 survey nights common pipistrelles scored in the High or Medium/High categories (ie activity was is in the 60th percentile or greater compared to all the comparison sites) on 70 occasions, equating to 59%.
While the available data is incompatible with the official IUCN Red List system it can be concluded that common pipistrelles in the Isle of Man are of Least Concern.
Soprano pipistrelle Pipistrellus pygmaeus
The soprano pipistrelle was accorded the status of a separate species in the mid 1990s on the basis of DNA analysis after bat workers noticed that pipistrelles seemed to call at two different frequencies. Manx Bat Group members had been recording both sonotypes but were now able to record them as two separate species. Unfortunately, several roosts had been previously located and identified as Pipistrelle and have yet to be re-checked to determine which species is present. Some of these have since been lost but there remain 15 or so that need to be checked. There are only four maternity roosts identified as soprano pipistrelles, one of which is the largest known roost on the island with over 200 individuals emerging. This is located in the north of the Island, where this species is most frequently encountered. Soprano pipistrelles have been recorded in 55% of the surveys and their recordings make up 10% of the total number of recordings made to date but there are one or two sites where the number of recordings of soprano pipistrelles outnumber those of common pipistrelles.
Soprano pipistrelles were present in 78% of the surveys analysed by Ecobat, 29% of them above the 60th percentile and the species is not considered endangered.
Nathusius’ pipistrelle Pipistrellus nathusii
Despite being only marginally larger than the other two species of pipistrelle found in the Britiah Isles, Nathusius’ pipistrelle is known to regularly make migrations of ca 1000km south-west from the Baltic countries to the Low Countries and north-east France, returning again the following spring. During the second half of the 20th C it began to be recorded from Scotland and North Sea oil platforms until a breeding colony was found in Northern Ireland. It was first detected in the Isle of Man in 2018 and has since been detected in 34 of the Bat Group’s surveys, 7% of the total. It has been detected at widely dispersed sites across the Island, from Castletown to the Ayres and Glenfaba to Garff. Interestingly, most recordings are only brief with the number of calls in single figures indicating that the bat is just passing through and there is only one site where the number of calls is in the hundreds, indicating feeding activity. No breeding roosts are yet known for this species but increasing numbers suggested by the records, and presence throughout the summer would suggest that breeding is taking place.
The site referred to above scored highly on the Ecobat system and the species was present in 6 of the 27 surveys analysed by Ecobat. Although only 2% of the surveys were above the 60th percentile this is seen as an encouraging figure for a species only to known to have been present since 2018.
Whiskered bat Myotis mystacinus
It is unclear when the whiskered bat first arrived on the Island since Wagstaffe’s reminiscence (1975) does not give a date for his observation of the species in the church outside Douglas, despite his earlier call, shared by others previously, for naturalists to look out for this species. Several roosts were discovered quite soon after the formation of the Manx Bat Group in 1990 but few in recent years. Of the even fewer that have been counted numbers have been quite modest. Nevertheless, whiskered bats have been recorded during 60% of the MBG acoustic surveys and although the recordings only account for 6% of the total recordings on occasions they indicate high activity levels. In fact 38% of the Ecobat analyses show this species to have activity above the 60th percentile, second only to common pipistrelle.
While more roost monitoring is required to gain a better understanding of population trends, the widespread distribution and occasional high activity levels indicates that there is little concern for this species.
Natterer’s bat Myotis nattereri
Despite the apparent population crash in the 1960s, which Stebbings (1988) considered might have represented most of the animals of that species on the Island, Natterer’s bats are again widespread, present in nearly a third, 31%, of the acoustic surveys. They are regarded as a quiet bat which need to be close to the detector, <10m, for their calls to be recorded so it is perhaps not surprising that their recorded calls represent only 1% of the total recordings. Despite this, Natterer’s bat calls are in the 60th percentile or above in 29% of the Ecobat analyses, the same figure as for Soprano pipistrelles, although at least three of these occurrences are for a winter hibernation site. All of the recorded roosts appear to be in the north, two of which were known to be occupied for 15 or more years up to 2010 but have not been checked recently. A large roost was discovered in 2022 and autumn swarming sites in 2024 and 2025.
The widespread distribution of the species and number of known roosts would suggest that this species is recovering well from its disaster in the 1960s.
Daubenton’s bat Myotis daubentonii
First recorded on the Calf of Man in 1961, caught in a bird net, it was not until 1990 that the species was recorded on the main island and by 1993 it was being recorded in several different locations, usually by its favoured habitat of still or slow-moving water. The more recent programme of acoustic surveys has now begun to record it away from water, and it appears in 25% of all surveys and comprising 5% of all recordings. In favoured localities it can exhibit high activity but makes only fleeting appearances in other habitats. Although present in 52% of the Ecobat analyses in only 22% of the survey nights are the number of recordings above the 60th percentile. No breeding roosts are known for Daubenton’s bats although a number of hibernation sites have been found, usually in masonry such as bridges but also mine buildings and underground features. Autumn warming sites were found in 2024 and 2025.
Without knowledge of its breeding localities the species might be considered vulnerable but it is present at all suitable localities that have been investigated, even newly created sites such as Ballanette Nature Reserve and the Manx Birdlife reserve at the Ayres showing that it can colonise new areas.
Leisler’s bat Nyctalus leisleri
The Leisler’s bat is another species first recorded in 1990, despite previous generations of naturalists searching for it. It has since progressed to be the second most frequently recorded species, occurring in 84% of the acoustic surveys, although accounting for only 6% of the recordings. The reason for that is probably that it is a strong, high flier with a loud call, picked up from up to 100m distance but it rarely stays in a locality for long as it hawks for insects at tree top level. It is present in 89% of the surveys analysed by Ecobat and has a High or Medium/High rating (>60th percentile) in 33% of those surveys.
Only seven roosts are known for Leisler’s bats, all bar one on the western side of Douglas. Nevertheless, as a relatively recent colonist (Pinder 2019) it seems that the population is still expanding.
Brown long-eared bat Plecotus auritus
The brown long-eared bat has been known to be present for a long time, the first record being in 1885. It is a conspicuous bat, often seen roosting in attics and large roof spaces and it is second only to common pipistrelle in terms of known maternity roosts, with 32 in total at present while more are discovered each year. Long-eared roosts are much smaller than pipistrelle roosts with the highest count being 33 and numbers in the teens or twenties being more common. The brown long-eared bat forages in a completely different way to other species, relying less on echo-location to find insects and more on direct hearing using their large ears. They fly closely round trees and bushes and pick insects off the foliage. It is said they can hear a beetle’s footsteps on a leaf from a metre away. It is not surprising then that they are almost at the bottom of the list in terms of the number of acoustic recordings made, at 1%, despite being recorded in 48% of the acoustic surveys. Similarly, they are present in 52% of the survey nights analysed by Ecobat but in only 4% do they achieve the 60th percentile or greater.
The large roof spaces selected by Brown long-eared bats are used for pre-emergence flights. Loft and barn conversions thus pose risks for the continuation of roosts and several roosts are known to have been lost in recent years. Mitigation is always proposed for those cases which pass through the planning process but it is not known how successful this often is. Consequently, brown long-eared bats could be considered under threat.
Lesser horseshoe bat Rhinolophus hipposiderus
Our most recently discovered species, confirmed as a resident in 2020. Until recently all records came from Rushen covering both winter and summer months. It has been detected during 5 of the acoustic surveys some of which have taken place in winter at a hibernation site where calls have nevertheless been recorded such that 4% of survey nights are above the 60th percentile. In March 2025 the species was confirmed as being present at a site in Maughold where it has since been recorded in every month of the year.
As a recent colonist with a small population its future cannot be said to be secure. It is not known even if there are enough bats to form a maternity colony but the Manx Bat Group will continue to monitor known sites and search for new ones in the hope of finding a maternity colony. Meanwhile, at least the known wintering site is secure.
The above analysis permits a table to be drawn up, along the lines employed by the BCT above, showing which categories the different species belong to. By definition the populations of Lesser Horseshoe bats and Nathusuis’ pipistrelles have increased but remain at a very low level, possibly perilously so for the Lesser Horseshoe. Population levels of Leisler’s bats have increased dramatically and also, arguably, those of Natterer’s bats and, possibly, Daubenton’s bats. Population levels of Whiskered bats, and Common and Soprano pipistrelles, have probably remained stable and, for pipistrelles at least, are large enough for the populations to be considered secure. While Brown long-eared bat populations could also be considered stable continued loss of roosts might put them at risk of future decline. The lack of knowledge of maternity roosts for Natterer’s and Daubenton’s bats is also of concern.
| Assessment of populations of Manx bats (using BCT categories) | |
| Increased | Stable |
| Leisler’s bat – secure with widespread distribution and reasonable population size | Common pipistrelle – secure with wide distributions, many known roosts and good population sizes Soprano pipistrelle – secure with wide distributions, many known roosts and good population sizes |
| Increased but at risk | Stable but at risk |
| Natterer’s bat – at risk from unknown population size, patchy distribution and very few known roosts Daubenton’s bat – at risk from unknown population size, patchy distribution and very few known roosts Nathusius’ pipistrelle – at risk because of low population size and no known roosts | Whiskered bat – at risk because of unknown population size and very few known roosts Brown long-eared bat – possible risk from continued loss of roosts from building developments |
| Insufficient data | |
| Lesser horseshoe bat – at risk because of extremely low numbers | |
Accordingly, it is probably safe to say that our bats are doing at least as well as those in the United Kingdom, if not better, although continued monitoring is required to ensure that all bat species in the Isle of Man continue to prosper. The Manx Bat Group will hope to achieve that, in part, with the recently drafted Biodiversity Action Plans for lesser horseshoe bats and the three species of Myotis bats.
References
Manx Wildlife Trust, https://www.mwt.im/state-nature-2024-bats, accessed 17/02/2024.
Pinder, N.J., 2019, Is the Leisler’s bat a come-over? Isle of Man Studies, XVI, pp 125 – 129.
Stebbings, R.E., 1988, Conservation of European Bats, 246 pp., Christopher Helm, London.
Wagstaffe, R., 1978, Looking for bats, Proceedings and Natural History Notes for the Area; The Liverpool Naturalists’ Field Club 1970 – 1978, pp 6 – 8.