I’ve been reading about the movements of bats named like hurricanes; Alex, Brenda, Carol, Dan. They were caught in the summer and tagged with radio-transmitters which allowed their positions to be triangulated throughout a night by surveyors moving through the landscape.
Tropical cyclones are monitored by satellites and radar, allowing scientists to interpret their likely path and point of landfall – similarly these bats require specialist techniques to monitor their movements and predict their patterns of behaviour.
The maps which result are like Google Maps for these animals which occupy the same space as us and use the same landscape, but do so under the cover of darkness, using a sense we cannot readily interpret, on a plane above us.
The roosts were found during the daytime – these are their places of rest and shelter, their equivalent of our homes. They might even be located in the same houses we inhabit, or in trees or culverts or caves.
Watching the bats leave the roost at night and then spread out into the landscape, their commuting routes were identified – these are the roads and footpaths they use to navigate around their environment. For the bats, these could be hedgerows or watercourses, tree lines or woodland edges; the vertical structure of the vegetation is important to allow their echolocation to guide them.
The bats were tracked to lakes, fields, woods and hedgerows where they spent time swooping and diving to capture their insect prey. These foraging areas are their retail outlets, supermarkets, restaurants and cafes.
A bat’s use of the landscape is complex and often individual; of the fourteen bats followed, no two were alike in their nightly habits. Some bats flew up to 20km in a night to reach their favoured foraging grounds, whilst others fed all night in the woodland they roost in. Species differed, sexes differed and individuals too, but some features could be highlighted as of the highest importance; nearly all the bats foraged over the lakes at some point – rather like we might all visit a supermarket – and the canal proved to be as busy as a motorway. Loss of these key resources could impact hundreds of individuals.
Bats also move house more frequently than we do and so the importance of different routes and foraging areas to an individual or colony will change throughout the year to as they seek the conditions they require – just as the roads in Devon and Cornwall swell to bursting in the summer whilst the shops and cafes can be dead in the winter. The same bat may occupy hibernation roosts, transitional roosts, maternity roosts, mating roosts, night roosts and others in between, but each is vital to a different stage of its life cycle.
Bats are a protected species, but their survival is dependent on much more than simply preserving a given roost. They are dependent upon an array of roosts, routes and foraging grounds which make their conservation much more complex than first sight might suggest. Take away their homes and they have nowhere to live; rip out tree lines and hedgerows, and they become isolated or dislocated; remove their foraging areas and they will starve.
The tension between conservation and development is often presented as a black-and-white choice – it’s people or wildlife. Do we allow species such as bats and newts to take precedence over people? This is generally a false dichotomy – both can be accommodated provided the needs of these creatures are understood, rather than simply assumed, and measures are put into place to protect natural infrastructure whilst developing our own.
If we simply supposed the paths of hurricanes and tornados, we would frequently get it wrong and the results could be catastrophic. Studies into the behaviour, structure and dynamics of our more enigmatic species allows us a chance to predict the impacts of our actions and take steps to minimise or avert their death and destruction. With our increasing understanding, we can hope to maintain the parallel landscapes of homes, roads and shops which overlay and intersect our own. We can then hope to preserve the species which rely upon them.
A lesser horseshoe being measured before release. Capturing and radiotagging bats provides us with valuable insights into the behaviour of these enigmatic creatures
Another Country Diary 