National Mammal Week 2020: Day 5: Broadleaved Woodlands
I am currently a second year PhD student at Sussex University, studying the conservation ecology of the rare barbastelle bat (Barbastella barbastellus). I am particularly interested in developing our understanding of barbastelle distribution at the landscape-scale and how these bats select the broadleaved woodland in which they form their maternity colonies. My research is being conducted as a collaboration between Sussex University and the Vincent Wildlife Trust.
Many of our UK bat species have adapted well to an urban lifestyle, roosting in buildings, bridges, tunnels, and artificial bat boxes. Some have adapted so well we may be tricked into thinking that they no longer require their natural habitat to persist… However, most of these species evolved to roost in trees and are still heavily reliant on areas of woodland habitat, at least for foraging. Whilst all our species may utilise woodlands, six are considered woodland specialists: Bechstein’s, Natterer’s, noctule, lesser horseshoe, brown long-eared, and barbastelle.
Broadleaved woodland, especially ancient woodland, is of particular value to bats as foraging and roosting sites. The comparatively high proportion of standing deadwood and mature trees provide opportunities for roosting, whereas the rich and diverse invertebrate communities provide an excellent foraging environment. It is our most complex terrestrial habitat, where soils have been left undisturbed for centuries and decaying wood has been left to rot to the benefit of both invertebrates and fungi.
The barbastelle is one of our rarest mammal species, partly due to its heavy reliance on ancient broadleaved woodland, which currently only covers around 2.4% of the UK. Agricultural and urban expansion are the leading causes of the loss of this habitat, but mismanaged woodland can also have a huge impact on woodland bats. Decaying, rotting, dead, or fallen trees are typically removed in order to maintain the “tidiness” of woodlands. It is a process that can have a significant effect on the woodland ecosystem, where up to a fifth of woodland species may be reliant on dead or decaying wood as part of their life cycle. Studies have demonstrated that there is typically more life in a dead tree than a living one!
Barbastelles have taken advantage of this unique ecosystem, coming together to form maternity colonies in the spring before giving birth to a single pup in late June to July. These colonies typically form under loose bark plates or within narrow cracks and fissures of standing dead oak trees (Quercus spp.), which are abundant in roosting opportunities. The scarcity of standing deadwood, even within ancient woodlands, may mean barbastelles require large areas of woodland to support their population given their tendency to switch between multiple roost trees. In August, juvenile barbastelles will become volant, initially flying in the local vicinity of their roost, where they will start to forage for themselves. Gradually, juveniles will follow their mothers further afield towards her foraging grounds, which may be up to 20km away!
The dark silky fur, pug-like nose, and large ears (that meet in the middle) of the barbastelle give it its distinctive appearance. Whilst its rarity may mean the chances of spotting it is low, new sites for these bats are still being discovered. Barbastelles are perhaps most easily identified from their distinctive “two-part” echolocation call, which can be recorded with the aid of an acoustic bat detector. Visiting ancient woodlands, especially those with streams and wet woodlands, will maximise your chances of spotting this elusive mammal.
Broadleaved woodland is also a sanctuary for many other rare bat species, such as the Bechstein’s bat (Myotis bechsteinii), which has a similar reliance on ancient woodland. This bat will generally roost in characteristically different cavities to that of the barbastelle, in particular deep cavities and woodpecker holes, and hence avoid any direct competition for space. Foxes, badgers, and hedgehogs are all familiar mammal species that also thrive within broadleaved woodland. However, the UK remains one of the least-wooded countries in Europe (covering just 13% of the total land area) and a collective effort is now needed to protect and restore these habitats before they deteriorate further.