Daubenton's bat (Myotis daubentonii) is a medium-sized species. It occurs throughout Europe up to about 63ºN, across to Korea and Japan. It is though to be increasing in numbers in parts of Europe. In Britain it is fairly widespread up to northern Scotland, in Ireland and the Isle of Man.

Despite severe loss of and damage to wetlands and waterways, Daubenton's bat seems to be increasing in parts of its range. This may, in part, be associated with increasing numbers of artificial water bodies, including gravel pits, reservoirs and flooded quarries. Also a low level of pollution may encourage a more consistent supply of certain chironomid midges.

However, the loss of diversity of aquatic insects has a detrimental effect on other animals and without the very careful control of pollution Daubenton's bats would be affected. the removal of waterside trees and disturbance to hibernation sites could also lead to a decline in this species.

flight & ultrasound

It has a steady flight, often within a few centimetres of the water surface and is reminiscent of a small hovercraft. Daubenton's bats take insects from close to the water surface. They have even been seen taking prey directly from the water surface, using their large feet as a gaff or the tail membrane as a scoop. They fly at about 25kph (15mph). 

They usually feed within about 6km of the roost but have been recorded following canals for up to 10km. It is thought that they need to drink more frequently than other species, hence the old name of 'water bat'  is quite appropriate. They often travel across land and occasionally feed away from water.

Like most bats they can eat copious amounts of insects each night. A 7-gramme Daubenton's bat often returns to its roost after an hour's feeding weighing 11 grams. That is a 57% increase in its body weight!

Daubenton's bat ultrasound calls range from 35 - 85 kHz and peak at 45 - 50 kHz. On a heterodyne bat detector the calls are a machine-gun like series of regular clicks for bursts of 5 to 10 seconds.

breeding

Mating takes place in the autumn and active males will seek out females throughout the winter. Maternity colonies, numbering between 40 to 80 bats but sometimes exceeding 100 individuals, consist almost entirely of adult females and are occupied from late spring sometimes until October. Young bats are suckled for several weeks and are fully weaned and able to forage for themselves at 6-8 weeks. Males or non-breeding females may aggregate during the summer to form their own communal roosts but sometimes join maternity colonies.

summer roosts

In England and Wales, the majority of known summer colonies are in humid, more or less underground sites near water. These may be tunnels or bridges over canals and rivers, or in caves, mines and cellars. They are only occasionally found in buildings, usually old stone buildings such as moated castles and waterworks. In Scotland colonies more frequently occur in houses.

Tree holes are probably much more widely used than the recorded evidence suggests and one individual was even observed entering a small hole in an earthen roadside bank! They also have bred in bat boxes.

Summer colonies are often quite noisy throughout the day, especially at sites where they are close to human activity. A variety of temporary night roosts are used, often in trees or tunnels close to their feeding sites. Daubenton's bats have been found clustering with Pipistrelles, Noctules, Natterer's and Brown Long-eared bats.

winter roosts

Many Daubenton's bats hibernate in caves, mines and other underground sites. In extensive tunnels systems with large numbers of bats present, Daubenton's are often the most numerous. They enter these winter sites in October but only small numbers are present in the early part of winter.

Numbers can increase dramatically towards the end of January and in February, and individuals often remain at these sites until the end of March or early April. Most are found in the warmer more stable environment within a site, although they can be found close to the entrance, particularly later in winter.

Although usually solitary, small groups of 3 or 4 are not uncommon. Individuals are often lodged in tight crevices; many being barely visible and it is likely that others are hidden away. They may also hide among rocks and scree on the floor of caves and tunnels. Thus, finding Daubenton's bats can be very difficult and it is likely that the numbers counted in many sites are a considerable underestimate of the numbers actually present.