First published in 2022 as Five more years of Manx Bat Records 2016 – 2020, Peregrine, 13, pp 241- 245
A previous article (Pinder 2018) summarised bat records collected by the Manx Bat Group (MBG) from its formation in 1990 to 2015, with emphasis on first records for the various species, including the Lesser horseshoe bat (Rhinolophus hipposiderus), identified as a possible vagrant by Selman (2014). This species has now been confirmed as resident (Samson & Pinder 2021) as has one further species, Nathusius’ pipistrelle (Pipistrellus nathusii) (Pinder 2020), although it is migratory throughout much of its range from northern France and southern England to the Baltic states and western Russia (Dietz & Kiefer 2014).
The impact of bat detectors on the collection of records was noted, permitting species identification without the need to catch and examine specimens, and mention was made of a new generation of detectors that show sonograms of the bat’s ultrasonic calls in real-time, increasing the accuracy of species identification. The MGP began to make use of such detectors in 2015, with an immediate impact on the number of records collected. Thus, 2015 was the first year in which more than 200 records were collected that number being in excess of 2,000 by 2020 and overall, generating an additional 3,801 records for the period 2016 to 2020.
Number of Records
As previously, the number of records for pipistrelles far exceeds that for any other species or species group and, perhaps by coincidence, the percentage these comprise of all records is remarkably similar: 45% compared to 47% for the earlier period. Of these pipistrelle records, 1,059 are for the
Common pipistrelle (Pipistrellus pipistrellus) and 504 for Soprano pipistrelle (Pipistrellus pygmaeus) with only 163 undifferentiated Pipistrellus species, a reversal of the earlier picture.
In addition to the much greater number of records each year, the greater accuracy of identification has reduced the proportion of records identified to only family or genus level. Records for Pipistrellus sp. now comprise only 10% of records for all pipistrelles and records for “bats” comprise only 2% of all bat records, compared to 70% and 16% respectively for records between 1990 and 2015. Only records for Myotis species remain relatively unaltered, and in fact have increased slightly, from 19% of all Myotis records to 23%, probably reflecting the difficulty of specifically identifying Myotis recordings even using sonogram analysis.
Number of Species Records
The frequency distribution of records to species level has altered considerably. For records assigned to species level, the Common Pipistrelle has now attained its rightful position as the most frequently recorded species, followed by Leisler’s bat (Nyctalus leisleri). The Brown long-eared bat (Plecotus auritus)has slipped to fifth place, overtaken by Soprano Pipistrelle and Whiskered bat (Myotis mystacinus) which is the most frequent of the three Myotis species. The other two Myotis bats, Natterer’s (Myotis nattereri) and Daubenton’s bat (Myotis daubentoni), come next with the last two places taken by the two recently discovered species, Nathusius’ pipistrelle and Lesser horseshoe bat, with 26 and 2 records respectively.
Car and Pedestrian Transects
The vehicle transects reported in the previous article (Pinder 2018) have not been repeated in a structured way in this later five-year period, only ad hoc transects being conducted in the northern parishes and the occasional transect returning home from an event in the south. In 2019, however, the Manx Bat Group organised Batsearch 19, a volunteer-based survey with 20 participants walking 1km transects with new bat detectors that record bat calls and their location purchased with a grant from the Manx Lottery Trust. Unfortunately, the Covid pandemic prevented the planned annual repeat of these surveys but it is hoped that they will be re-instated in the future. Batsearch 19 contributed 1583 records to the data base and periodic repetition, if not annual, over the long term will begin to reveal trends in the fortunes of bats in the Isle of Man.
Geographical Distribution of Records
It is considered that the species order for the later period more accurately reflects population levels, with the proviso that Leisler’s bat may be over-recorded owing to its strong, loud call and the Brown long-eared bat perhaps under-recorded owing to its quiet call. Nevertheless, both these species have been recorded in every parish or local authority area. In fact, discounting the two recently discovered species, Nathusius’ pipistrelle and Lesser horseshoe bat, most local authority areas have records for all seven of the established species. Only six of the 23 local authority areas, Port Erin, Ramsey, Douglas and Castletown of the built-up districts and Arbory and Marown of the rural parishes have fewer than seven, with between one and five species. The various bat species are therefore well distributed across the Island and there are now bat records for every 10 km grid square on the Island, even SC 36 which comprises approximately 99% sea.
The UK National Grid is the basis for mapping the distribution of all biological records, at various scales down to 1 x 1 km squares. Manx bat records can now be viewed in atlas form on https://isleofman.nbnatlas.org/ giving a better indication of the geographic distribution of species than hitherto. However, the data set still suffers from the observer effect since records can only be obtained from locations visited by bat workers with detectors or where static detectors are left in place. Survey effort is not random and is frequently dictated by required response to planning applications as well as directed effort to obtain records for nature reserves and specific habitats.
It is probably premature to attempt to construct distribution maps for our bat species and viewing the various species on the NBN Atlas usually shows a scattering of points throughout the low ground of the Island. There is a very interesting indication however, that the distribution of the Soprano pipistrelle is not as uniform across the island as is the case for the Common pipistrelle or any of the other bat species. Within the seven northern parishes the average proportion of Soprano pipistrelle records to all pipistrelles is 37% and for the 15 other local authority districts it is 13%. There appears to be a distinct bias towards the northern plain whereas common pipistrelles are as frequent in the south as they are in the north.
The Soprano pipistrelle is considered by all authorities to favour riparian woodlands and according to Dietz & Kiefer (2014) it avoids agricultural areas and grassland. Yet the northern parishes from Lezayre round to Michael comprise largely grassland with only the Sulby River providing riparian habitat. Elsewhere, the lowlands of the east, west and south contain rivers such as; the Dhoo, Glass, Laxey, Santon, Neb, Co;lby and Silverburn rivers all with associated woodlands but apparently not many soprano pipistrelles. It is tempting to speculate that the extensive beaches around the north of the island provide a foraging habitat lacking elsewhere, with hatches of seaweed flies regularly appearing at the strandline. Allen Moore has suggested that this may be a reason that choughs do comparatively well in the Isle of Man but this idea has not yet been tested thoroughly for bats. There are, however, a few records from surveys conducted at the Ayres and Lhen beaches indicating almost equal activity of Common and Soprano pipistrelles.
Winter records
The hill land appears largely devoid of records on the distribution maps for all species, although there are some records from vehicle-based transects over the Mountain Road and Round Table, plus an intriguing single record of a hibernating Brown long-eared bat in the old Murray’s Motorcycle Museum at the Bungalow. There are 169 records in what might be considered the hibernation period for bats, November to March, though in actual fact the majority of records in this time period are of active bats flying past a detector during surveys. Only twenty records could be said to pertain to hibernating bats including five of bats in bat boxes. The MBG has renewed and extended its bat box scheme in recent years, partly thanks to a grant from the Manx Lottery Trust enabling the purchase of durable (non-timber) bat boxes, and now operates bat box schemes in four locations and monitors five other locations for DEFA and private landowners.
Breeding Records
The MBG also monitors known summer breeding roosts of bats, of which there were 239 in the database. There are known maternity roosts of six of our nine species, Daubenton’s bat being one of the missing species along with the Lesser horseshoe bat and Nathusius’ pipistrelle. There are currently insufficient volunteers within the bat group to monitor every roost every summer though, in recent years, the MBG has started contributing to the UK National Bat Monitoring Project Roost Monitoring Scheme, leading to an increase in the number of roosts for which counts of emerging bats are obtained from an average of 17 roosts per year to an average of 55.
Most roost counts are conducted by MBG members, although a small number of householders volunteer to count their own bats. Similarly, most records are submitted by members of the Group though members of the public can, and do, submit records using a form on the web site, www.manxbatgroup.org and the MBG hereby places on record its appreciation for any and all records submitted. It is only through the accumulation of records that a definitive picture of the distribution and population levels of our various bat species will be acquired.