Daubenton’s bat, often called the water bat because of its predilection for hunting over lakes and rivers, is a medium-sized bat, weighing up to 12 g and with a
wingspan of up to 250 mm. It is not
dissimilar in appearance to whiskered and Brandt’s bats. The redbrown fur on the back is uniform in colour and smooth in appearance, the chest and belly are paler. The rounded face is pale and hairless
around the eyes. The pointed ears are low on the side of the head. Daubenton’s bats have proportionally larger feet than other British bats, with bristles on the toes. They
use these specialised feet to grab insects from the surface of the water.
Daubenton’s bats echolocate using
frequency modulation from 30 to 90kHz. On a heterodyne bat detector set to about 50 kHz this sounds like a series of short clicks, often described as a ‘machine-gun rattle’. The bats can be seen flying low and slow, close to the surface of lakes, ponds, canals and rivers.
Although usually associated with slow-flowing water courses, they are still found over smoother sections of some of Cornwall’s fast flowing rivers. Daubenton’s bats roost in trees and buildings and often within the structure of bridges, conveniently close to their feeding grounds. In the winter they hibernate in caves and mine workings where they may lodge themselves into cracks in the rock or cluster together.
One Daubenton’s bat had to be rescued from a house in Truro when it decided to set up home on a clothes rack.
© Paul McNie
The droppings of the Daubenton’s bat, when fresh, are noticeably moister than those of other similar-sized species, and may be found near roosts in tunnels or under bridges.
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Daubenton’s bats prefer to hunt over smooth water. Ripples may interfere with their echolocation. In captivity they have been seen to catch small fish from near the water surface.
Daubenton’s bats mainly hunt across the surface of water, using echolocation to identify emerging water insects such as midges and mayflies. The bat catches these by trailing its large feet across the surface, and also by scooping up prey with its expanded tail membranes.
The bats roost close to their hunting areas, frequently in old trees close to the river bank, or under bridges or tunnels. They are often found sharing roosts with other species, especially pipistrelles and noctules. Roosts can be quite raucous during the day, especially in urban settings.
The bats mate in the autumn and may continue to mate in hibernation roosts. The females ovulate in the spring, giving birth to a single pup in mid-summer. Although all females do not breed every year some tagged females had pups in every year that they were studied.
Maternity roosts may have as many as 100, or as few as 15, nursing mothers, while males roost singly or in small numbers during the summer. Bats often move roost sites during the summer. They leave the roost between 10 and 80 minutes after sunset and move together to hunting areas where individuals may defend small feeding areas.
In the autumn, swarms of Daubenton’s bats may be seen around hibernation sites, these are mainly males and the reason behind this swarming is unclear. From December onwards they move into hibernation roosts in caves and tunnels, where they may be the most common species present. They are normally found individually or in small groups, wedged in cracks and gaps or even on the floor under rocks.
Disturbance of roost and hibernation sites has a direct impact on populations of Daubenton’s bats. Their use of bridges and tunnels as roost sites mean they can be disturbed when repairs take place. Their numbers seem to be stable or increasing possibly as a result of greater areas of open water, and improvements in water quality over recent years. However, they can also take advantage of nutrient-enriched water, feeding on pollution tolerant insects.
Daubenton’s bat is recorded across Cornwall, although it is not common and is thought to be under-recorded. It is strongly associated with open water. Daubenton’s bat occurs throughout the UK and Ireland and from Western Europe to Japan.
Subject to the extensive legal protection of all British bats, the barbastelle is also included on both the UK and local BAPs. It has also been identified as globally threatened and decliningA widely
distributed bat which is not regarded as being at risk of extinction, althoughit is subject to extensive legal protection in the UK. Work by the Bat Conservation Trust indicate that the population of Daubenton’s bats in the UK is stable.
Monitoring of summer maternity roosts and hibernation roosts by licensed bat
workers. Mist net trapping by licensed bat workers. Emergence surveys. Bat detector monitoring. Cat kills and incidental reports.