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Daubenton's Bat

Daubenton’s Bat was first described in 1817 by the German naturalist Heinrich Kuhl (1797-1821). The name commemorates the French naturalist Louis-Jean-Marie Daubenton (1716-1799). Daubenton’s Bat is one of the medium sized Myotis species found in the UK. It has a body mass of 7-15 grams, a wingspan of 240-275 mm and a forearm length of 33-42 mm. The dorsal fur is a uniform red brown, with pale ventral fur. The face is pink with bare skin present around the eyes. Daubenton’s Bats echolocate at between 32 and 88 kHz, with a peak frequency of around 45 to 55 kHz. On a bat detector calls are heard as a rapid series of regular clicks, with many texts likening this to a machine-gun-like burst.

Daubenton’s Bats feed almost exclusively over water and their diet consists mostly of chironomid midges with other insects such as caddisflies and mayflies also taken. Rivers and still waters are both utilised and studies on foraging behaviour on an upland river in northern England have revealed a preference for foraging on stretches of river where the water surface is smooth and both banks are lined with trees (Warren et al., 2000). Flight is fast and direct with the bats foraging within the first one metre of airspace above the surface of the water. Insect prey is taken out of the air, or from the surface of the water. The latter method involves the use of their large hind feet and the tail membrane. The prey is then quickly transferred to the mouth. Daubenton’s Bats usually feed within three km of their roost sites but have been recorded following canals for up to 15 km (Altringham, 2003).

Daubenton’s Bat roosts are normally found close to water and summer roosts are found in tree holes, bridges, tunnels, caves, mines and cellars. Buildings are also used. Hibernation roosts are often underground in caves, mines and cellars. This species will aggregate with others and mixed roosts with Natterer’s Bat Myotis nattereri, pipistrelles and Brown Long-eared Bats Plecotus auritus have been recorded. Studies undertaken on the roosting habits of Daubenton’s Bats have shown that the different sexes tend to roost in different sites. Male bats show a tendency to roost at higher altitudes where foraging conditions are more challenging, with female roosts located at lower altitudes (Russo, 2002). Further research undertaken in the Yorkshire Dales suggests that male Daubenton’s Bats feeding at higher altitudes have been excluded from the better feeding grounds at lower altitudes by females and dominant males (Senior et al, 2005).

Daubenton’s Bats are widespread and common throughout the UK with an estimated breeding population of around 560,000. However the accuracy of this estimate is questionable with Harris et al. (1995) estimating a combined breeding population for England, Scotland and Wales at 150,000. The remaining 410,000 comes from a separate population assessment for Northern Ireland (Bat Conservation Trust, 2012). Latest trend data for this species suggests the UK population is stable and possibly increasing in some areas (Bat Conservation Trust, 2012). This is despite the loss of, and damage to, wetlands and waterways. The species becomes rarer in northern Scotland and is believed to be absent from Shetland, Orkney and many of the Western Isles.

Mennell and Perkins (1864) described what is likely to be the earliest record of Daubenton’s Bats in the northeast of England. The record dates from 1839 of a bat taken from Auckland St Andrew, Durham and subsequently preserved at Durham University. The bat was erroneously identified, by the Rev. L. Jenyens, as a distinct species and named Vespertilio oedilis. However, a later inspection by Keyserling and Blasius suggested that the characteristics of the specimen used to distinguish it from Daubenton’s Bats were the parts most likely to be distorted when the specimen was dried and stuffed. Keyserling and Blasius concluded that there was not enough evidence to separate the specimen from Daubenton’s Bat. A further examination by Rev. Jenyens convinced him that it was a white variety of Daubenton’s Bat.

George Bolam (1926) wrote several accounts of Daubenton’s Bats from the region between 1880 and 1920. His earliest account is from a site one or two miles north of Berwick-upon-Tweed, which may or may not be north of the Border. He recalls that his then young brothers brought home a fishing creel full of bats taken from an old willow tree in 1880, which could be the earliest roost record for the region. The following morning 15 were described as “available for inspection” and all were Daubenton’s Bats. Eight were adults and the others were described as unfledged young in varying stages of development. This confirms that it was a breeding roost. Bolam described Daubenton’s Bats as being well distributed and not uncommon throughout the district where suitable conditions prevail. He states that this species was found in most such places investigated in Northumberland. He recalls bats being found at Alston, Tweedside (both sides of the border), Tillside, and the River Aln. His account also details the measurements of various specimens from Seaton Delaval and Chopwell, dated 1917, and from Houxty dated 1920.

Current field records of Daubenton’s Bats are numerous throughout the region and our maps unsurprisingly show a pattern of distribution along all of our major water courses from the River Tweed in the north to Easington Beck on the Cleveland/North Yorkshire border. Records exist from the upper reaches of the rivers, such as upstream of Kielder and Cow Green reservoirs, down to the east coast at Alnmouth, Lynemouth, Castle Eden Dene and the Tees Barrage. However the current distribution maps clearly show that the middle reaches of the rivers hold the most records. There do appear to be some gaps in the distribution, notably the absence from many of the smaller water courses in the Hartlepool area (Ian Bond, pers. comm., 2012). Sightings of Daubenton’s Bats are not restricted to large water bodies; several members of the Durham Bat Group, including the author, have witnessed Daubenton’s Bats feeding over a small isolated pond near Butterwick, Sedgefield. With the exception of seasonally dry ditches this pond lies over one km from any other water courses and two and a half km from the nearest major water bodies of Crookfoot and Hurworth Burn reservoirs. Radio tracking undertaken near Morpeth in May 2012 revealed Daubenton’s Bats feeding over a pond approximately one km from the nearest river. The bat was caught feeding over the pond and eventually found roosting in a church almost eight km away (T. Wiffen, pers. comm., 2012).

A trip along any of the region’s major waterways is likely to reveal the presence of Daubenton’s Bats, with anglers frequently encountering them when fishing into the late evening. One record, which could probably be attributed to this species, comes from an angler night fishing above the Rose Tree Bridge at Shincliffe around 2007. The angler, known personally to the author, stated that a bat bumped into the side of his head and attached itself to his scalp, screeching in his ear as he tried to remove it. Perhaps there is a little truth behind the old wives’ tale after all! In the moments leading up to the incident, which left him rather shaken, he reported that numerous bats were seen near the remains of an old bridge and flying along the stretch of river.

MARS Daubenton's bat

The first modern recorded roost in the region was from the Durham/North Yorkshire border at Croft-on-Tees. The roost was found under the A167 road bridge in 1985. Since then a further 15 roosts have been identified across County Durham including one in a bridge over the River Leven near Yarm. Further south a hibernation roost has been recorded in a tunnel at the Boulby potash mine in South Cleveland. Roost sizes vary from single bats to a count of 118 in 2004 from a road bridge at Piercebridge. Maternity roosts of 71 bats and 85 bats were discovered via radio tracking by the National Trust at Gibside, Gateshead, in 2009 and 2010. One roost was found in a bridge over the river Derwent and the other in a relatively modern house.

In Northumberland 11 roosts are known with modern records dating back to 1986. Northumberland can certainly claim the largest known roost in the region with a count of 419 from a church at Brinkburn. This roost was the subject of a study by Newcastle University into the effects of a music festival on the emergence behaviour of breeding bats. The study revealed that while the festival did not significantly affect the numbers of bats emerging from the roost, it did impact upon the time of emergence; with bats leaving up to 47 minutes later on festival nights (Shirley et al, 2001).

Roosting sites vary. The majority of known roosts in County Durham are found in bridges, but in Northumberland the majority are known from buildings, including dwelling houses. A single roost is known from a bat box. The Boulby roost in Cleveland is located within a tunnel. This variation in roosting sites appears to be consistent with the national picture although very few tree roosts are known from our region. It is unclear whether this is due to roost selection by the bats or whether it is down to surveyor effort: bridges and buildings are generally easier to locate and survey than tree roosts.

The majority of the known roosts in the North East are summer roosts. Only four hibernation sites are known: three of these are from upper Weardale and one is from Boulby. Surveys in upper Teesdale between 1997 and 1999 revealed high numbers of Daubenton’s Bats in August. The possibility that this was part of a migratory pattern to upland, underground hibernation sites cannot be ruled out.

References

Written by Barry Anderson (last updated Nov 12)