The Natterer’s Bat Myotis nattereri was first described in Germany in 1817 and was named after an Austrian naturalist called Johann Natterer (1787-1843). Natterer’s Bat was first mentioned in Britain in 1837 (Barrett-Hamilton and Hinton, 1921) though evidence has been found in Neolithic strata (10,000-5,000 years BC) in Dowel Cave, Derbyshire (Yalden, 1986). Natterer’s Bat is found throughout the country up to the Great Glen fault in Scotland with a higher density to the south. They are considered widespread and fairly common in Northumberland and widespread but less common in Durham.
Natterer’s Bat is a medium sized Myotis bat with broad, pointed wings and long light-brown fur on the upper side and white or nearly white beneath. It has a long narrow ear with a sharply pointed, straight sided tragus. The face and snout are pink to light-brown and the wing membranes are mid-brown. The bats have a quiet echolocation when foraging and are quiet in the roost and so are often unobserved by roost owners. The bats emerge when it is nearly dark and they are near-invisible against buildings and vegetation. Natterer’s Bat is an agile flyer with the ability to hover and manoeuvre around foliage to glean its prey; it could be described as the harrier of the bat world with a good turn of speed when needed, often seen when a pair of courting bats are flying fast in tandem.
A wide range of prey species are eaten as the bat can take non-flying prey such as harvestmen, spiders, weevils and earwigs by gleaning them from foliage as well as catching diurnal flies such as dung-flies, crane-flies and blow-flies when at rest or disturbed. Sheltered semi-natural deciduous woodland associated with waterways are the preferred foraging area, but semi-natural deciduous woodland can suffice. Natterer’s Bat has also been seen foraging low over ruderal plants, such as docks, in an open field margin close to Darlington. This versatility of foraging habitat types is an important factor, allowing this species to be widespread. Natterer’s Bats are thought to fly up to four km and occasionally six km from their roost to foraging areas (Smith and Racey, 2002).
The first historical record noted for Natterer’s Bat in the North East was reported in the Tyneside Naturalists’ Field Club publication in 1867 where they stated “We can only record one instance of the capture of this species, but so little attention has been made to the bats of our district that this and other species may probably be more generally distributed and less rare than is usually supposed.” The record was for a tree in Hoffal Wood, Durham by W. Backhouse (Mennell and Perkins, 1864).
George Bolam (1926) states that prior to his records no reports of Natterer’s Bat were known in Northumberland with the closest in Carlisle and Yorkshire, and two suspect records from Dalkeith and Argyllshire in 1880 and 1858 respectively. Bolam first recorded the Natterer’s Bat in 1916 close to Alston both in flight and as a casualty (brought in by a cat), casualties proving the most accurate way of identifying bats at the time, though observation was also used as Bolam noted the differences in the flight between Whiskered Bat Myotis mystacinus and Natterer’s Bat. Other sightings of Natterer’s Bat on the wing were also noted within a short distance of Alston by Bolam.
When the Durham and Northumberland Bat Groups were first formed in the 1980s, more records for Natterer’s Bats were identified, but the quantity of records was low and the Distribution Atlas of Bats in Britain and Ireland 1980-1999 (Richardson, 2000) showed their distribution in the region to be sparse and scattered. However the 21st century has seen the number of Natterer’s Bat records increasing as legislation was enforced and redundant or historic buildings that are also used by this species were surveyed prior to conversion or renovation. This increase in survey effort along with additional methods of bat identification has identified many more roosts and increased what we know of the distribution of the species in the North East.
In northeast England an average sized maternity roost is approximately 23-35 adult bats, based on Northumberland Bat Group Records, but a large roost is known in a church in North Yorkshire with about 150 bats. Natterer’s Bat is versatile when it comes to roosting sites, but crevices are the favoured choice and they roost frequently in trees. Table 1 summarises roost types where maternity roosts have been identified by the author in northeast England, with a bias towards buildings. Natterer’s Bats may use loft spaces as daytime roosts or before they emerge at dusk, however generally they will exit from an eaves/ridge crevice and commute directly to the closest sheltered feeding area. Mean emergence times for these roosts were 22 minutes after sunset for first emergence up to 42 minutes after sunset for the last bat to emerge, based on 20 roosts with counts throughout the season. Two further roosts had first emergence before sunset, but both these roosts were adjacent to excellent woodland foraging areas. Previous research has quoted first emergence times at 31 minutes with median emergence at 60 minutes, but these results are worldwide with no latitude or dates mentioned (Jones and Rydell, 1994).
Table 1. Roosting Positions and Types for Natterer’s Bat in northeast England
|Building Type||No.*||Crevice Type||No.*||Roost Exit Type||No.*|
|House – traditional large built buildings||10||Below the ridge tile and above the ridge board||11||Open doorways||7|
|Barn||10||Crevices in stonework/rubble fill||3||Ridge||6|
|Outbuilding||4||Between stone wall and woodwork||3||Gable Apex||4|
|Castle||1||Hanging from the ridge board||1||Masonry Crevice||2|
|* based on 32 roosts||* based on 23 roosts||*based on 28 roosts|
The most common place that Natterer’s Bat has been observed roosting in the North East is beneath stone ridge tiles where droppings are seen filtering through a gap between the ridge and sarking boards. When this type of crevice is used in barns or outbuildings the bats often exit through open doorways. Roosts of Natterer’s Bats can also be found on any side of the building including the north side, where cooler roosts are located. Maternity roosts are also known in bridges, churches and bat boxes in the region. Natterer’s Bats often roost in the same buildings/roof spaces as other species especially Brown Long-eared Bats Plecotus auritus and Daubenton’s Bats Myotis daubentonii.
One population of Natterer’s Bat is known to use Belsay Castle during warm summers though they appear to seek alternative accommodation in wet cold summers such as those of 2009-2011. The castle roost is between the ceiling timber and stonework of the Great Hall with the exit some distance away via a garderobe. Cooler crevices in stonework and vaulted rooms are used as transitional/hibernation sites. An alternative summer roost is a south-facing masonry crevice in a blocked doorway of a nearby house and this roost is usually active when the bats are absent from the castle as they have been in recent years. A local culvert also has evidence of explorative Natterer’s Bat and may also be used as a swarming/hibernation site. Hibernation roosts are sought in structures where low temperatures remain constant such as culverts, castles, icehouses, caves and mines or wall cavities, and are usually in tight crevices where predators cannot reach them. Very few hibernation sites for Natterer’s Bat are known in Northumberland and Durham. Natterer’s Bats are also known to travel to swarming sites in autumn probably for mating purposes, as high gene diversity has been identified (Rivers et al, 2006). Distances between swarming sites and summer roosts have been shown to be about 24.8 km for Natterer’s Bats (Parsons and Jones, 2003).
Natterer’s Bats are found frequently throughout Northumberland with 100 recorded roosts; however records in Durham are sparser with fewer maternity roosts and only scattered records of occasional or foraging Natterer’s Bats. The distribution in Northumberland becomes sparser in the industrial areas in the southeast and in the upland areas above 244 metres in the west. These parameters may also explain the distribution in Durham, as both counties have low levels of ancient semi-natural woodland compared with the rest of the country and both have a good proportion of land above 224 metres. This species of bat may also be under-recorded due to tree roosts being rarely identified.
Written by Ruth Hadden (last updated Nov 12)