Second article from Bat Conservation Trust: first published in CJS Weekly Friday 4 December 2015

Logo:  Bat Conservation Trust

Bats are hibernating… but we are not

As you walk along the park or your street you have surely noticed that winter is here; trees are almost bare, you can’t see any house martins or swallows in the sky nor hear the piercing calls of swifts. Bat enthusiasts in particular miss not being able to watch bats during the twilight hours since they hibernate during the winter months.

Natterer’s bat hibernating at Highgate’s tunnels. (c) Jess Barker/
Natterer’s bat hibernating at Highgate’s tunnels. (c) Jess Barker/

Hibernation is an ingenious way for these small flying mammals to endure the cold winter. It allows them to lower their metabolism to save energy as flying insects are harder to find over the winter months. They have prepared for this moment in the autumn by eating as many insects as possible; this increased their fat reserves which they are now using as fuel to survive hibernation. During this torpor period, bats can lower their temperature to an amazing 2°C!

While bats are fast “asleep” the work at Bat Conservation Trust (BCT) does not stop. As they say “The show must go on!” And indeed it does. During winter, our National Bat Helpline still gets an average of 15 calls per day from concerned callers, mainly regarding bat care advice for grounded/injured bats, planning enquiries (i.e. people concerned that building works or infra-structure might affect a roost or bats) and enquiries about repairs and maintenance that could affect bats.

Natterer’s bat hibernating at Highgate’s tunnels. (c) Jess Barker/
Natterer’s bat hibernating at Highgate’s tunnels. (c) Jess Barker/

In addition BCT keeps monitoring bat populations during the winter months thanks to the efforts of volunteers contributing data to the Hibernation Survey as part of the National Bat Monitoring Programme NBMP), which has been in place since 1997. In these surveys, experienced and appropriately licensed bat workers check and count bats in hibernation sites which typically consist of caves, mines and other underground structures such as cellars or ice houses. During the survey these dedicated citizen scientists thoroughly search for any bat species in crevices or open spaces along a standard route.

Last winter more than 120 volunteers submitted hibernation counts from around 500 sites. The data collected enables us to produce statistically robust species population trends for seven species that are widely recorded at hibernation sites. Other species are too rarely recorded toenable trends to be produced, either because they are very rare in the UK (the most extreme example being the UK’s only known greater mouse-eared bat that is found hibernating at the same site each year) or their hibernation locations are not yet known or are difficult to access (e.g. tree holes). Included in the latter category are common and soprano pipistrelles, our most commonly recorded species in the summer, but very elusive in the winter due to their tendency to hide themselves away in places that are inaccessible to people.Hibernation surveyors also look for any signs of white-nose syndrome (WNS) which has killed millions of bats in the USA. While the fungus associated with WNS has been identified on a number of bats in Europe, these observations have not been linked to mass mortalities and therefore WNS has not been confirmed in Europe, but it is important to remain vigilant for any possible signs of WNS.

Hibernation surveys are an important element of the NBMP as they enable data to be collected on a wide range of species, usually with a high degree of confidence in species identification. Through the National Bat Monitoring Programme, BCT also runs a number of summer surveys that anyone can take part in and help us monitor how the UK’s bat populations are faring and inform conservation strategies.

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Posted On: 04/09/2015

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