Mammals found on the trail and the story of the Daubenton bat!
Level 1: The mammal species list for the nature trail is longer than one might expect for a small island in the Broads. Each of these species is seen most years: otter (frequently sighted in both river and Broad), fox, grey squirrel, stoat, Reeve’s muntjac deer, wood mouse, bank vole, common and water shrew, water vole and several bat species: noctule, serotine, common and soprano pipistrelles, barbastelle and Daubenton’s.
So, how do these species get to an island? The bats of course can fly, but the rest? They swim! Yes, even squirrels and deer, both of which have been seen by the wardens capably crossing rivers. A fox has been spotted delicately balancing along the narrow top of a gate across the entrance to the Broad. And although we don’t have any here, we have heard several eye-witness accounts of moles swimming in the Broads too! For these animals, the nature trail and Larkbush Island offer two things: a quieter place in the middle of the Broads to raise a family, and a hunting ground. Foxes eat waterfowl and small mammals, grey squirrels eat bird’s eggs and nestlings, bank voles clear up crumbs dropped by wardens and the bats enjoy the rich invertebrate life that is a vital part of this ecosystem.
Level 2: We have 18 species of bats in the UK, 17 of which breed here. Many species are declining due to loss of habitat and lack of invertebrate food; all bats in the UK eat invertebrates. A little pipistrelle bat can eat 3000 midges in one night, hooray! The larger species eat big moths and beetles, which they can eat while flying in the dark. All our bats hunt using echolocation; they shout out noises as they fly along and use the resulting echo bouncing back to their ears from prey items to calculate where the prey is. Some people can hear the noises bats make, but for most it is easier to use a bat detector, which convert the sounds so they can be heard by people or record them as data points.
Some of the species recorded at the Trail will be the same as those visiting your garden, but there’s one that is associated with areas of slow-moving water, which we will focus on here: Daubenton’s bat.
Its scientific name is Myotis daubentonii: it was named after Louis-Jean-Marie Daubenton, a French naturalist. Myotis refers to the ‘mouse-eared’ bats from the Greek mus = mouse. It is a medium-sized bat with a wingspan of 24-27.5cm and an average weight of 7-12g. It is a species so closely associated with waterways that another name for it is the ‘water bat’. Daubenton’s feed on midges, caddisflies and other small flies, which they can scoop from the water’s surface with their feet or the web of skin between feet and tail. They prefer to roost near the water, in tunnels or bridges, or holes in trees. In the winter, like all other UK bats, they hibernate, choosing caves, tunnels or mines. During the summer the females form colonies to have their pups.
Level 3: There are an estimated 150 000 Daubenton’s bats in Great Britain. They are not a species of conservation concern, however the global biodiversity crisis threatening the mass extinction of invertebrates would surely impact on the status of a predator species entirely reliant on invertebrates for food. The removal of waterside trees and damage to wetlands can also damage populations. (In some locations Daubenton’s bat appears to be increasing, possibly due to the creation of artificial water bodies such as flooded gravel pits and their ability to support invertebrates.)
If you use a bat detector to search for them, their echolocation calls peak at 45-50kHz and sound like 5-10 second bursts of machine gun fire. The best way to find them is by watching a stretch of calm water, like a slow-moving river, canal or lake at dawn or dusk. The ‘water bat’ flies in fairly straight lines low over the water, with a slower flight speed than some but still reaching up to 25km/h When we host ‘bat walks’ at the Trail, we usually see Daubenton’s at the end of the walk, about 9:30pm, when we arrive back at the river. Looking along the stretch of water, using red-light torches to cause little or no disturbance to these bats (which show avoidance of white light sources but appear unaffected by red light), we can watch them fly just above the surface picking off prey.
We do not know of any colony sites or well-used roosts near to the Trail, but Daubenton’s will fly 6km in a night searching for food. A colony is most likely to be in a tree hole, with an average 20 to 50 bats suckling young for 6 to 8 weeks. They are also known to breed in bat boxes occasionally. Males and non-breeding females will sometimes join these maternity colonies, but more often roost separately, sometimes with other species such as pipistrelle, brown long-eared or noctule.
Top Bat Facts!
Bats generally: 18 species in Britain.
Daubenton’s bat. Myotis daubentonii. Myotis refers to the ‘mouse-eared’ bats from Greek mus = mouse. Named in honour of Louis-Jean-Marie Daubenton, a French naturalist.
Wingspan 240-275mm. Weighs 7-12g. Lives 4-4.5 years. Closely associated with waterways, where they feed on midges, caddisflies and other small flies. They can scoop these from the waters’ surface with their feet or the web of skin between feet and tail. They prefer to roost near the water, in tunnels or bridges, or holes in trees. But in winter they go underground to hibernate, in caves, tunnels or mines. During the summer the mothers form colonies to have their pups.
If you use a bat detector to search for them, their echolocation calls peak at 45-50kHz and sound like 5-10 second bursts of machine gun fire. The best way to find them is by watching a stretch of calm water, like a slow-moving river, canal or lake at dawn or dusk. The ‘water bat’ flies in fairly straight lines low over the water seeking prey.
There is an estimated 150 000 Daubenton’s bats in Great Britain. They are not a species of conservation concern, however the current extinction event affecting numbers of invertebrates globally has the potential to impact on bat populations too.