What do bats do in winter?
In Britain there are 18 species of resident bats, 16 of which occur in Devon; they feed largely on moths, flies, beetles and other flying insects and are mainly active from spring to autumn. However, from late autumn to early spring their food – flying insects – is too scarce to meet their energetic demands of high body temperature and flight, so during winter, bats have to reduce their energy demands. They do this by reducing their body temperature to that of their surroundings, resulting in slower breathing and a lower metabolic rate. In this state, known as ’torpor’, a bat may breathe less than once an hour.
Different species of bat choose different winter roost sites. They roost in cool, moist or dry places such as caves, mines, tunnels, cellars, cavity walls and tree cavities; they will also roost in unheated buildings and some roost in bat boxes, or in crevices in rocks or trees. Hibernation lasts from late October through to April, so in autumn bats need to feed a lot in order to build up their fat reserves to last them through the winter. By November most bats are hibernating and starting to use their fat reserves. Later in winter bats may leave the roost on warmer nights to feed and drink. In autumn some species of bat may migrate to hibernate on the continent.
During 2018 and for the next two years, Devon Wildlife Trust is running a survey of bats in Devon using bat detectors placed in different locations in the county. Anyone can apply to take part and the detectors pick up bat calls and record them digitally. When the detector is returned to the bat survey workers, the data is analysed and you get a report on which bats are using your garden (or wherever the detector was deployed). I have a small rural garden and took part in the survey last year; during the three nights it was deployed, the bat detector recorded nine or ten different species of bat. The vast majority of bat contacts were of Common or Soprano pipistrelles, but other bats included Daubenton’s, Noctule, Lesser horseshoe, Long-eared, Serotine and Barbastelle.
The bat detection equipment is very easy to use and there are detailed instructions. If you would like to know more about which bats are using your garden (or park, or meadow, etc.), and how many, see Devon Greater Horseshoe Bat Project – Devon Bat Survey at www.devonbatproject.org and click on ‘Borrow a bat detector’ for further details. It’s free to take part and this year’s bat survey starts again from April onwards. You can also sign up for newsletters with further details of the survey.
In recent years, bat numbers have declined for a number of reasons. Some of Devon’s bats, such as the Greater and Lesser horseshoe bats, are rare and the numbers found in Devon are of national importance. I know of at least one house in a nearby village which has a summer (maternity) roost of Lesser horseshoe bats in the garage. Might you be lucky enough to have bats using your house or garden? You may like to know that sharing your home with bats poses no health hazard. They do not build nests, gnaw wood, or chew cables. They are also not blind and will not get tangled in your hair!
Anthony John