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Noctule

Noctule by Terry Coult

The Noctule is one of the larger British bats, with a length of 3.7 to 4.8 cm and a wingspan of 32 to 40 cm. Typically they weigh around 28 to 35 grams but can be as much as 40 grams. Its fur is dark yellowish-brown (Corbet and Southern, 1977).

This species is normally associated with woodland habitat and with river valleys, roost sites being in most cases in old woodpecker holes (Boonman, 2000) and in rotten trees. Roosts in buildings are unusual, though other structures may be used, as in the case of the Lockhaugh Viaduct in the Derwent Valley. It is generally the first bat on the wing in an evening, often being seen in the light of the setting sun and sometimes appearing as the Swifts Apus apus, which have a similar wingspan, disappear.

Noctule prey consists mainly of larger insects such as beetles (Jones, 1995) and the deep dives observed in hunting contrast with the high and steady flight of animals commuting from their roosts to their hunting areas. Noctules may travel considerable distances to feed; in Europe commuting ranges of up to 26 km have been noted (Gebbard and Bogdanowicz, 2004).

The Noctule is widely distributed throughout Europe up to 60° N, though it is virtually absent from Spain, Portugal and southern France (Schober and Grimmberger, 1989). It is widely distributed in England and Wales, but scarce in Scotland. It is absent from Ireland, where its congener, Leisler’s Bat Nyctalus leisleri, is widespread. In the UK the data from the National Bat Monitoring Programme Field Survey suggests a slight increase in population from the index year of 1999 to 2009, but the trend is not significant.

The earliest known occurrence of Noctule in the North East is a “fine specimen” taken at Cleadon in 1836 and presented to the Natural History Society by W.A. Swinburne. This appears in Mennell and Perkins (1864) as a Serotine Bat Eptesicus serotinus, but the identification was subsequently corrected by W.D. Roebuck in 1884 (Bolam, 1926). Bolam regarded it as a “rare accidental visitor”. He also recorded two sightings from the Tyne Valley (June 1914 and October 1923), but regarded these as fitting into a pattern of migratory vagrancy.

The Noctule may well be under-recorded in the North East, in part because it rarely roosts in buildings occupied by humans. Car transect surveys in Durham have located Noctules in locations in open countryside well away from known roosts. Our map shows a wide distribution, particularly along the river valleys, with occurrences as far west as OS grid references NY66 and NY68.

Most recorded roosts number below 50, although separate sites in the Riding Mill area were counted at 130 and 64 in 1985. Since Noctules do move from one site to another during the breeding season these two counts may refer to the same colony.

More recently, on 2 May 2011, a colony of 69 was counted out of an Oak tree Quercus robur in Gosforth Park Nature Reserve. Three days later there were about 30 in that tree and a similar number in a Birch tree Betula pendula elsewhere in the reserve. By 12 May there were again 69 in the oak, but on 19 May there were five in the birch and none in the oak (T. Wiffen, pers. comm., 2011). In late May 2012 over 40 Noctules were foraging over Bothal Pond. One was caught and radio tagged by Northumberland Nathusius’ Project and led observers to a roost in a Beech tree Fagus sylvatica a little over two km away. An emergence of 49 was counted on the first night and 54 the second. The following day only 26 emerged and did not include the tagged bat, which was re-located on the fifth day in a pine tree some 5.5 km from the first roost; 37 bats were counted out of the pine, but there were then none in the original beech tree (T. Wiffen, pers. comm., 2012).

Tree roosts are typical, but there is a count of 52 in a manor house near Snod’s Edge in May 1986. This site is also associated with an unexplained piece of behaviour when the main part of the colony arrived from elsewhere and entered the roost about 35 minutes after sunset (Strachan, 1986). Lockhaugh Viaduct has been monitored regularly by John Durkin since 1985, the maximum count of 44 being achieved in 1992, though 4-10 is more usual and in some years the species has not been found (J. Durkin, pers. comm., 2012) There is an intriguing January 2010 report from a member of the public of a bat which appeared to be a Noctule alighting on the disused Lands Viaduct near Cockfield, crawling up the brickwork and “investigating holes and cracks” (N. Jackson, pers. comm., 2010).

Hibernation normally remains undetected, but in January 1986 an Elm tree Ulmus minor was felled on farmland on the outskirts of Darlington, knocking a hollow branch off a neighbouring Beech. Twenty-one Noctules fell with the branch; two died, but the remaining 19 were cared for and hand-fed for just over a week before being returned to the site in a hibernation box which was strapped to the tree. When the box was re-checked in May there was one dead bat inside, but 47 live Noctules in the Beech tree. By late June they had moved on.

Other hibernation records come from Fenwick, near Matfen (one found on the ground in January 2008), the Hart to Haswell Tunnel (singles in March 2005 and in February 2012) and from Croft Bridge (singles in March 1989 and in winter 1989/90).

The Hamsterley Forest bat box scheme provides evidence of use, with Noctules found in seven out of 22 years, 1987 to 1996 and 2000 to 2011. On one occasion, in July 2000, nine were present in one box, while two males were found together in July 2006. Other occurrences were of single occupancy of boxes and there are a number of other occasions over the years when droppings thought to be from Noctules have been found. The pattern may suggest opportunistic, rather than strategic, use of boxes; it might be noted that a typical bat box slit is rather different from the species’ preferred woodpecker hole.

Evidence of movements between roosts and feeding areas is provided by an observation in May 2008, when at least 41 Noctules were around the Houghton Gate area (Evans, 2008). A follow-up visit three days later showed fewer bats, but they were leaving Lambton Park, which contains mature woodland, and heading just west of south. This direction would lead in an almost direct line to three areas where feeding has been noted in the past (Durham Bat Group records). In the 1950s and 1960s large numbers were reported feeding over the North Tees marshes, where there is no suitable roosting habitat, but numbers are much reduced in recent years. They seem to arrive late here when little light remains, but may commute down Greatham Creek and may also arrive from other directions.

Insect prey varies over the course of the summer. Cockchafers Melolontha melolontha may be popular when available. In a note on Cockchafer emergence from grassland which had once been an ancient lawn at Ryhope, one observer recorded that “they were being munched in their hundreds by a bunch of Noctules” (Lupton, pers. comm. to Durham Bat Group, 2011), while on 27 May 2009 at Crimdon Dene Noctule feeding was associated with “large beetles flying around and … one … was positively identified as a cockchafer beetle” (J. Jones, pers. comm., 2009). On 6 August 2007, 50-75 Noctules were noted in a “ball” about 10 metres across feeding on “hairy legged juicy flies” just above head height in the Druridge Bay area (R. Hadden, pers. comm., 2012). On 27 June 2011 six Noctules were noted feeding on ghost moths at a fairly low level over a small plantation on Cowsley Lane, near Lanchester.

In the North East most other feeding groups are relatively small, though 50+ were watched over the surface of the river at Wylam Bridge on 25 May 2007 (R. Hadden, pers. comm., 2012), and over 20 have been noted at Drinkfield Marsh, Darlington and at Crimdon Dene (I. Bond, pers. comm., 2012.). In 2008 24 were recorded commuting along Thorpe Bulmer Dene, which connects to Crimdon Dene, but numbers were lower when the survey was repeated in 2011. John Durkin’s maximum for Shibdon Pond is 16 (pers. comm., 2012) There is a mid-November record of several feeding over Stapleton Pond, about one km south of the Durham/North Yorkshire county boundary, around noon on a mild day (I. Bond, pers. comm., 2012.).

Near Witton-le-Wear on 31 August 2010 several Noctules were foraging, but “quite a bit higher and moving across from the south to the north were a group of what were definitely Noctules. There were about 10 bats flying in a fairly tight group and their flight was not as purposeful as you would normally describe commuting. They were not foraging and it looked like there was some interaction between bats within the group.” (Gilchrist, pers. comm. to Durham Bat Group, 2010).

MARS Noctule

What appears to have been a Noctule carrying a young bat in loops over a 10 metre stretch of stream in Billingham Beck Country Park was recorded and photographed by Ian Forrest in 2008 (Bond, 2008).

There are fewer large roost counts in the North East now than there were in the 1980s and 1990s. There is some anecdotal evidence of lower numbers feeding at two sites in northwest Durham, though this could be governed by changes in prey abundance. There are also fewer Noctule roosts reported but there is a much more widespread distribution of recent field records. In the additional light of the fairly stable trend suggested by the National Bat Monitoring Programme it is difficult to draw firm conclusions on the health of our population of Noctules.

References

Written by David Sowerbutts (last updated Nov 12)