Easegill Caves Hibernation Surveys

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!

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Hibernating drone flies

It’s autumn and those creatures which hibernate through the winter are beginning to make their preparations. The squirrels are out burying nuts to tide them through, the bats are fattening up on insects to see them through torpor and those invertebrates which sleep the winter away are looking for safe places to stay.

A likely indicator of a hibernating insect is an early appearance in the spring. This is true of the brimstone butterflies which, for many, heralds the start of spring, and also the rather ungainly named drone fly. This is actually a hoverfly – Eristalis tenax – which is named not for the sound it makes in flight but for its similarity to a honey worker bee, a drone. These flies can often be seen early in the springtime, taking advantage of the first available nectar sources such as the lesser celandine pictured below.

Drone fly - Eristalis tenax - on a lesser celendine
Drone fly – Eristalis tenax – on a lesser celendine

We visited Tattershall Castle last weekend – a National Trust property out near Lincoln – and spotted several of these drone flies investigating crevices and cavities in the roof of the kitchen at the ground floor of the castle. You descend here down a small flight of steps and this movement below the ground will appeal to the hoverflies – conditions tend to be more stable and remain above freezing when you are beneath the ground level. Stability of conditions is often as important as suitable temperatures – a stable environment means less false signals that spring is here and emerging from hibernation too soon is never a good idea!

Drone fly investigating a hibernation site at Tattershall Castle
Drone fly investigating a hibernation site at Tattershall Castle

The hoverflies were not alone – tattered small tortoiseshells and red admiral butterflies were also checking up and down the walls for a safe place to roost for the winter whilst herald moths were already settled and looking set to sleep until spring.

Tree bumblebees in Grantham

Bumblebees are fascinating insects and I have been meaning to learn more about them for a long time. I’m not sure that it doesn’t have something to do with the fact that they looks quite so similar to colourful bats up close… there is something about their furry round bodies which is rather reminiscent!

It is still very early in the season but most of our UK species respond to conditions rather than dates and when the sun is shining and the weather is mild, many hibernating species will come out of torpor and begin their spring routines. I have recorded pipistrelle bats in flight over the last week; the birds are certainly thinking about nesting with the early species such as long-tailed tits gathering nesting materials; and there was quite a gathering of bees on a very early flowering blackthorn on Monday lunchtime.

I managed to get a couple of photographs of this bumblebee and decided that this would be the first ID on my path to learning more about these species. And it looks as though I picked quite a good one – my tentative ID of a tree bumblebee (Bombus hypnorum) was confirmed by helpful tweeters @sbd08simon and @ed_p_wildlife. Apparently there is no other bee which this species can easily be confused with – the colouration is just black and buff-brown with a white tail. No coloured bands! This bee has quite a simple pattern compared with the multitude of variations which other species seem to manage! This guide from Bumblebee Conservation gives a great introduction to identifying bumblebees.

Tree bumblebee Bombus hypnorumAlthough I am, as already confessed, no expert, I believe this must be a queen out foraging and potentially searching for a nesting site. The queens emerge in spring (usually March or April) and scope out potential nesting sites before laying their eggs. About six weeks later, the eggs hatch and the entirely female workforce splits into teams, some foraging for the colony, others staying in the nest to do the housework. Later in the year, ‘reproductives’ are produced – these are virgin queens and/or drones. The drones will die after mating with a female but the queens will hibernate through the winter and emerge when the temperatures warm up in the spring and the cycle can begin again. I would therefore suppose that my bumblebee feeding in February is a queen freshly emerged from a relatively short winter’s sleep.

Tree bumblebees are so called because of their habit of nesting in trees – either in woodpecker holes or more frequently, in nest boxes. Like most species, they have adapted to inhabit the world we have created around them and can also be found nesting in houses, in soffit boxes and similar features. Some other species of bumblebee will occupy similar niches but the preference for these tree (or tree-like) nesting sites is most notable in the tree bumblebee. Many other UK species will nest underground and you can often see them bumbling into the undergrowth towards the entrances to their underground homes.

Tree bumblebees are a relatively new additional to the UK’s fauna – they first appeared in Wiltshire in 2001 and have been spreading north every since. It is believed that they are natural colonisers which have established under their own steam, much like the collared dove which was a rare vagrant until the 1950’s when they were first recorded breeding here and now grace most garden bird tables across the UK. The invasion of the tree bumblebee appears, so far, to be benign with no observed impacts upon existing native bee populations and its spread appears to be continuing with the first recording in Scotland last year.

I have recorded my sighting here – the data gathered from recordings around the country can be used to study this species and describe its distribution around the country.

If you want to read more about the tree bumblebee, there is a very informative factsheet available from Bumblebee Conservation.

Tree bumblebee Bombus hypnorum on Blackthorn Prunus spinosa