Nathusius’ Pipistrelle is one of three pipistrelle species known to be resident in the UK. A relatively uniformly coloured small brown bat, it is slightly larger and heavier than both the Common Pipistrelle Pipistrellus pipistrellus and the Soprano Pipistrelle Pipistrellus pygmaeus. Adults weigh between 6 and 10 grams and have longer wings than the other two pipistrelle species, though there is some overlap in forearm length with Common Pipistrelle (Dietz et al, 2009). Morphological characteristics are well described by Dietz et al. (2009) though the dentition characteristics described are not always definitive; a confirmed Nathusius’ Pipistrelle in Northumberland in 2011 did not exhibit the upper jaw, first pre-molar alignment described (Tina Wiffen, pers. comm., 2011).
Nathusius’ Pipistrelle echolocation calls are typical pipistrelle type calls which generally have a frequency of maximum energy (FmaxE) or peak frequency of 35 to 40 kHz. However, caution needs be exercised when identifying Nathusius’ Pipistrelle by echolocation call alone in the field as there can be overlap with the FmaxE of Common Pipistrelle calls depending on the situation. A Nathusius’ Pipistrelle rescued in Northumberland in 2011 and identified by morphology and DNA analysis was recorded shortly after being released from the hand calling with a FmaxE of 43 kHz. The author has also frequently recorded Common Pipistrelles emitting open habitat calls with a FMaxE of 40 kHz or slightly under 40 kHz. The continuing trend for the use of broadband bat detectors and recorders and computer analysis of the recordings is likely to increase the reliability of species identification from echolocation calls and may result in more verifiable records.
The Nathusius’ Pipistrelle is often regarded in the UK as a species very closely associated with water bodies. Water bodies, including relatively small water bodies and wide slow-flowing rivers, are certainly utilised and in Northumberland offer the most reliable chance of encountering the species. However, in Europe the species is also regarded as a bat of deciduous mixed woodland and damp lowland forests, as well as riparian forests, and can also be found hunting in built-up areas, particularly during migration (Dietz et al, 2009), so we should not assume that the species will only be found at water bodies. Typical recorded diet consists entirely of flying insects, dominated by waterborne diptera but also caddis flies, aphids and lacewings (Dietz et al, 2009).
Long running ringing studies have demonstrated that the species undergoes long-distance seasonal migrations in continental Europe between breeding grounds in the north and east and hibernation areas in the south and west. The longest known annual movement is 1,905 km (Hutterer et al, 2005). Major migration routes tend to be along the coast and major river valleys but Nathusius’ Pipistrelles are known to make sea crossings of several hundreds of kilometres (Ahlen et al, 2009; Pravettoni, 2011). It has been speculated that Nathusius’ Pipistrelle migrate between northeast England and Norway (Pravettoni, 2011), but the author is not aware of any research that confirms this to be true. The speculation may stem from an over-interpretation of the known direction of migration on the continent against a map published by Russ et al. (2001) that plots North Sea records of Nathusius’ Pipistrelle found on ships, as a block of records mid-way between Norway and northeast England.
However, it is clear that Nathusius’ Pipistrelle migrate into northeast England in autumn, generally from the east. It is less clear whether these migratory bats remain here for the winter or pass through, or perhaps there is a combination of both. Two Nathusius’ Pipistrelle confirmed in the hand in Durham and Teesside were a female rescued from a Magpie’s Pica pica beak at Hendon Docks on 8 September 2010 and a male found at Hartlepool Power Station on 24 September 2010. The Sunderland individual was associated by date with a weather-influenced “fall” of migratory birds from the continent. This may shed some light on how these bats migrate across wide stretches of sea. Reports received by the author about a site on the Kent coast also note the arrival of Nathusius’ Pipistrelles (detected by automatic detectors) within hours of another weather-influenced fall of migratory birds (Matt Hobbs, pers. comm., 2012). On 17 September 2011 an under-weight and dehydrated male Nathusius’ Pipistrelle of that year was recovered from Newbiggin-by-the-Sea, Northumberland, having been observed by bird watchers to fly in from the North Sea before “crashing to the ground” and then crawling down a gap beside a loose fence post. Wind direction on the previous days had been from the south or east making it highly unlikely that the bat had been blown out to sea from the UK. The bat was rehabilitated and released.
The first confirmed record of Nathusius’ Pipistrelle in Northumberland is of an adult male found under the back door thresh of a house in the village of Throphill in December 2007. The bat was reportedly found when the householder went to investigate why the door thresh squeaked every time it was stood on! The season suggests hibernation in the county. Ruth Hadden also received a downed male from a vet in Northumberland in June 2008 but unfortunately the vet had taken no history when accepting the bat so the exact location of where it was found is unknown.
Durham’s earliest accepted record dates from 1999 when Geoff Billington recorded Nathusius’ Pipistrelle over the Tees at Cotherstone and near Bowes (Durham Bat Group, 1999). There is also a record from a small ornamental lake at Whitworth Hall near Brancepeth on 3 May 2000. While this was an identification by heterodyne detector in the field it is regarded as robust by Durham Bat Group because several members were involved in the observation of at least three bats foraging. There is another confirmed record of one bat at Wolsingham in July 2009 where a recording was taken. Nathusius’ Pipistrelle has also been recorded in County Durham at Tunstall Reservoir in 2009 and in Cleveland at Crockfoot and Lockwood Beck Reservoirs in 2009, at Scaling Dam reservoir in 2010 and at Lockwood Beck Reservoir in 2011. All these were recorded in September as part of the annual Bat Conservation Trust’s (BCT) Nathusius’ Pipistrelle survey. Other “possible” Nathusius’ Pipistrelle records come from Stewart Park, Middlesbrough in 2008 and Ormesby Hall grounds, Middlesbrough in June 2009.
Teesside boasts the earliest North East record with Wardhaugh (1994) reporting that a Nathusius’ Pipistrelle was found at Teesport on 26 April 1991 though he notes that “it seems highly likely that this animal arrived in Britain by ship”. Arrivals of Nathusius’ Pipistrelle into the UK by ship are probably not uncommon. Giles Manners recovered three Nathusius’ Pipistrelles found in a load of timber in a yard in Shildon, County Durham in December 2011. The timber originated from near Hanover in Germany and was transported by road via a timber yard in the Market Harborough area of Leicestershire. There are similar reports from elsewhere in the country. Not all ship-borne arrivals of Nathusius’ Pipistrelle may have joined ship in continental ports. Some may have joined mid-crossing as migratory birds sometimes do. Sander Lagerveld reported a Nathusius’ Pipistrelle alighting on a boat in the North Sea 100 km north of Den Helder, Netherlands in September 2006. The bat arrived from the east and remained for half an hour before continuing to fly west (Sander Lagerveld, pers. comm., 2012). Though the location is fairly far south of this publication’s area of interest, this anecdotal record further illustrates the potential for these bats making long distance sea crossings from Scandinavia to the UK. Records of Nathusius’ Pipistrelle found on oil rigs in the North Sea certainly point to those bats having arrived there under their own steam. Records of the species being found on ships and oil rigs in the North Sea increased significantly between the mid-1980s and 2001 (Russ et al, 2001) and this trend has continued after 2001 (Russ, pers. comm., January 2012).
As well as an influx of migratory bats, there is undoubtedly also a resident population of Nathusius’ Pipistrelle in the North East. Targeted survey work by Northumberland Bat Group, BCT and The Northumberland Nathusius Project during 2011 and 2012 has recorded Nathusius’ Pipistrelle present in coastal areas of south Northumberland in every month between March and October. The species has been recorded at Bothal, Wansbeck Riverside Country Park at Ashington, Queen Elizabeth II Country Park near Ashington, Ladyburn Lake at Druridge Bay Country Park, Druridge Pools, East Chevington, Cresswell Pond, Low Hauxley and Warkworth. The species has been recorded throughout the year at several of these sites and co-ordinated surveys on one night in September 2011 found the species present at seven different sites up to 13.5 km apart at the same time. Whether this is a breeding population remains to be proven. Currently there are only two known maternity roosts in mainland UK, the nearest of which is in Lincolnshire, though Nathusius’ Pipistrelles have been recorded in bat boxes in East Yorkshire in 2008 and 2010 (Russ, pers. comm., 2012).
The Nathusius’ Pipistrelles in the North East may be part of a mixed gender breeding population, though to date this can not be confirmed. Equally, the possibility that there is a resident male population supplemented by females at certain times of year can not be discounted, though again neither can it be proven at present. That male Nathusius’ Pipistrelles are present in autumn and at least attempting to mate in Northumberland is known. Social calls which are understood to be male mating calls were recorded in Northumberland in 2011 at several locations, including by the author near Bothal, by Hazel Makepeace at Ladyburn Lake, by Lee Miller at Queen Elizabeth II Country Park and by Tina Wiffen at Low Hauxley. Whether these attempts to attract a mate were successful is unknown.
It has been suggested that Nathusius’ Pipistrelle is undergoing an expansion in range in response to climate change (Lundy et al, 2010). It may be that Nathusius’ Pipistrelle has been under-recorded in the past or it may be that the species is becoming established in the region as this account is being published. While we still have much to learn about all bat species, perhaps Nathusius’ Pipistrelle offers the greatest scope for new discoveries over the next decade or so?
Written by Graeme Smart (last updated Nov 12)