The Cumbria Bat Group kindly let me come along on a hibernation survey at Easegill Caves in January 2017. We hiked up to Upper and Lower Kirk Caves to see what we could find, then descended using ropes and caving ladders into Link Pot to explore an underground cave network some 15m down.
We found good numbers of myotis species including Daubenton’s, Natterer’s and whiskered/Brandt’s/Alcathoe – these last three are grouped as it’s very difficult to distinguish these three without disturbing the bats. We also found a small number of brown long-eared bats hibernating too.
It’s important to note that disturbing hibernating bats is illegal without a licence from Natural England – this survey was led and supervised by licenced bat workers who ensured that disturbance was kept to a minimum whilst allowing the bats to be identified and counted. If you find a bat in roosting you should take great care not to disturb it especially during the winter as they may rouse from torpor at an inappropriate time and be unable to then survive the winter. If you do find a roosting bat – let your local Bat Group know! More details at the bottom…
The video below shows a summary of the seven hours we spent out in the hills, in just under three minutes!
The following photographs show a few of the hibernating bats we identified on the surveys.
It’s not only bats we found in the caves – plenty of cave spiders and hibernating moths too including herald and tissue moths.
If you would like to get more involved with your local bat group and help out on hibernation surveys such as these, you can find your nearest here. Many thanks to the South Cumbria Bat Group, and Rich Flight in particular, for a great opportunity to explore the caves and see plenty of roosting bats!
It’s very nearly Halloween – what better time to introduce you to the bats which haunt Grantham Canal when darkness falls…
I spent several nights this September cycling along Grantham Canal with an EM3 bat detector connected to a GPS unit, recording the bats in flight between the A1 to the east and Hickling Basin to the west. Bats use echolocation to navigate and hunt and the bat detector converts this ultrasonic sound into something we can hear. The sound emitted by the detector tells you when a bat is there, often which species it is and sometimes even what it is doing.
You might imagine that this is quite a sinister place to be, surrounded by bats on a moonlit night, but there really is nothing to be afraid of! As the detector tapped and pattered away to announce their, I could see bats flying before me in the darkness. But even though I was cycling towards them, they elegantly avoided me every time, never making contact and certainly never tangling in my hair. This is one of the most enduring myths about bats but their fantastic echolocation abilities mean that they can ‘see’ and avoid obstacles on even the darkest of nights.
I recorded at least five species in September, some calls with ‘buzzes’ indicating foraging and some with ‘song flight’ where male soprano pipistrelles emit lower frequency social calls to attract mates. These are just on the edge of human hearing and can be heard without a detector – you may have heard the very high frequency chirrups if you walk outside at dusk in the autumn.
The common pipistrelle is our most abundant species in the UK, and was encountered throughout the route of the canal, particularly where there are more trees as this species specialises in hunting along ‘edge’ habitat which is typically along hedges, tree lines and other landscape features.
The soprano pipistrelle is very similar morphologically and was not even identified as a separate species until 1992. Now they can be told apart confidently in their hand, and with fair reliability acoustically as the soprano pipistrelle calls at 55 kHz compared with the common pipipstrelle at 45 kHz. In England, the soprano pipistrelle is often found associated with water and so it was no surprise to find them along the canal. An interesting observation however is that there appears to be much more activity to the east, near to larger water bodies. Denton Reservoir lies just beside the canal towards the eastern end and is likely to be an important foraging resource for this species.
The vast majority of the recordings related to these two pipistrelle species – the other bat species were found at much lower frequencies.
The noctule bat is our largest species and tends to fly high and early, often the first bat to appear around sunset and can be seen in the skies as the swifts are still on the wing. Only one noctule was heard during the transects, between Denton and Woolesthorpe and picked up again near Muston. This bat is large and the sky was light meaning I could watch it flying my way, foraging as it flew to the west. This is a widespread species which favours roosting in trees, but numbers are generally lower than the pipistrelles.
Brown long-eared bat
Brown long-eared bat is one of our quietest but most charismatic bats. Their large ears make them quite charming to behold, and they are frequently found roosting in barns and other buildings. I only picked up a single instance of this bat, but their very quiet echolocation means they are generally under-recorded.
The myotis bats are considered to be some of the most difficult to identify from sound alone. Daubenton’s bats are the myotis species most frequently associated with water as they specialise in flying low over still waters and taking insects on the wing or from the water’s surface. Natterer’s bat is another myotis species and some of the calls recorded along the canal in September are characteristic of this species. Whiskered and Brandt’s bats are the other two myotis species which are likely to be present in this part of the country. These two bats are very similar to one another and are difficult to separate even in the hand. Some of the calls have the characteristics of one (or both) of these two species. Whilst these species are not commonly associated with aquatic habitats, the canal also boasts hedgerows, copses and grass bank margins which provide great terrestrial habitat as well.
I encountered a whole host of other species whilst cycling along in the afterglow of sunset including barn owls, tawny owls, hares fleeing down the towpath and badgers snuffling in the hedgerows. The canal is stunning in the daytime but at night it comes alive with a whole host of new species – a walk around sunset might reveal creatures which you would not normally be privilegedenough to watch.
My last professional bat survey of the season was completed last week – at a railway tunnel which is a swarming site for a small number of bats. Swarming sites are locations, often caves, mines or tunnels, where bats – particularly the myotis species – gather in the autumn to mate. We stayed until 5h after sunset to monitor the usage of the tunnel and recorded around 5-6 bats at this site. They are most likely to be Natterer’s bats, judging by the calls, although myotis species are notoriously similar acoustically, and can be difficult to tell apart from sound alone.
The bats were using the tunnel entrance – a great, ominous opening onto blackness surrounded by shrubs and trees – but they spent most of their time flying in tandem within the tunnel and especially around the vertical air vents – circular ‘chimneys’ some 5m wide – which are spaced out down the length of the tunnel.
I’ve recently bought a trail cam and this seemed like a good opportunity to try it out and answer the first question – can it be triggered by bats? I’ve spoken to people who have said that they can, but that the lag between the detection and the shutter closing means that the bat has been and gone before you can get a good photo.
I’ve opted for the Bushnell Trophy Cam Max HD, largely because of the no-glow LED’s which would hopefully reduce the risk of it being spotted and interfered with, but I wasn’t sure how the different cameras available would compare on their sensitivity. It can certainly spot a greenfinch hopping about on the lawn which suggests it is reasonably sensitive to small creatures, but my first test on bats suggested that flight ~6m away was not detected.
I placed the trail cam face-up beneath one of the air vents and there were no ‘triggers’ but I also used the ‘field scan’ setting to automatically take a 10 second video every 5 minutes, regardless of whether the camera detected something to monitor. The result was lots of empty shots, with only dripping water to reveal movement, but I did record one brief pass of two bats flying close together. It’s not great footage – very far from something you might have seen on the BBC recently using their high quality night vision kit – but it is enough to show that the bats are there and it could potentially be a way to monitor the presence of bats in a site such as this over a period of time.
The use of automated bat detectors has really taken off in recent years – this is a great supplement to surveys where ecologists walk or watch and detect bats using hand held devices. A static unit can sit in the field for a week, record every bat which goes past, and be picked up and analysed at your convenience. It lacks the qualitative element which can be gained from an actual surveyor in the field – where did the bat fly, which direction, what behaviour – but it is invaluable to assess the assemblage of bats present, picking up species present at low densities or passage use by rarer species.
In a similar way, I am hoping that the trail cam will be a great way to gather a census of the species of mammals in an area or at least using a trail, even if they only pass that way once a week. With any luck, watch this space for further updates and footage which are hopefully a little better than this!
If anybody has any experience of catching videos of bats in flight using a trail cam, I’d love to hear about it!