The Diffusion of Useful Knowledge

Having a first degree in history I have always had an interest in how our understanding of bats has developed down the years (see "An 1892 bat-worker", January 2009). Today's post brought me a copy of "The Penny Magazine of the Society for the diffusion of useful knowledge", published on 7 January 1843.

My first thought was what a wonderful-sounding title and what a sign of the times that there existed a Society for the Diffusion of Useful Knowledge. The Victorian moneyed classes were incredible busy-bodies and loved trying to enhance people's lives, often in rather idiosyncratic ways. (Strangely, paying people enough to live on was rarely considered a way of enhancing lives!)

A regular feature of this paper is a series entitled "Curiosities of British Natural History" and this issue's feature is about bats. Sadly, the author's name is not given but it was either someone who knew the subject or who did a good deal of research as it contains several pages of detailed description of the subject.

Above the start is a gorgeous engraving, showing a Noctule, a Pipistrelle and a Long-eared Bat. The latter has a thoroughly cheesy grin on its face and the Noctule looks too portly to fly, but some of the anatomy is surprisingly detailed: presumably they were engraved from dead specimens.

The article begins with the enticing statement "It may surprise some of our readers to be informed that sixteen or seventeen distinct species of bats are natives of the British Isles". What?! That is our current understanding (depending on whether you include the Greater Mouse-eared or not). In 1843 the two Pipistrelles had not been separated, nor had Brandts and Whiskered Bats. The finding of Nathusius Pipistrelles in Britain was long in the future and, although it had been described elsewhere, I don't think the Grey Long-eared had been discovered in Britain at that time.


So what were the other four species? Unfortunately, the anonymous author doesn't tell us. In fact he only describes eight species, dismissing all the others as "extremely rare and restricted to certain localities". Was he guessing? Was he reading a foreign book and assuming the same species were here? Was he including some long-dismissed sub-species or perhaps bats found in part of the Empire? How frustrating!


The species he describes are: The Common Bat (Pipistrelle); The Great Bat (Noctule); The Long-eared Bat; The Barbastelle; The Reddish-grey Bat (Natterer's); the Whiskered Bat and the Greater and Lesser Horseshoe Bats. The obvious missing species is the Daubenton's, which must surely have been known at that time and would have been relatively easy to distinguish.

As with all writing of the era, wordsmithing was a priority and some of the descriptive text is fantastic: "Often during warm summer evenings have we seen numbers, perhaps several scores, of the Common Bat flitting over pools, in chase of gnats and similar insects, or gambolling with each other in a mazy dance, ever and anon uttering sharp shrill cries of exultation and delight..." The shill calls were presumably social calls, which are sometimes just within the range of human hearing. Incidentally, a score at that time was an innocent number twenty, in case you think the author was using dried bats for questionable purposes.


The piece includes a surprising amount of scientific detail, for example listing the species found to hibernate in caves as Natterer's, Whiskereds, Barbastelles and Long-eareds, though again Daubenton's are conspicuously absent (could it be they confused them with Natterer's at this time?). Given that this was a popular paper, not a scientific journal, there is a remarkable amount of detail: something today's press could learn from.


As with today's press however, the author just can't resist a lurid story and describes bats stealing bacon from chimneys and eating meat in larders. Not perhaps as daft as it sounds, in an era when bacon was hung in chimneys to cure and when meat was kept open in a larder. Houses would have been quite porous to bats at that time and I can imagine a stray Pipistrelle within a house, finding itself next to a joint of raw meat, having a nibble, possibly for the water content.


Something exciting about old texts like this is when they describe the location of bat roosts. The author mentions a Noctule roost under the eaves of Queen's College Cambridge and Greater Horseshoes occupying caves "at Clifton and in Kent's Hole, near Torquay". If anyone reading this lives in those areas, it would be fascinating to know if these sites are still occupied, 166 years later!


At the time this paper was produced, people were still grasping to understand how bats found their way in the dark, and, reading the author's description one gets a sense of his frustration: they knew there was something special about it, but couldn't quite put their finger on it:


"There is a singular property with which the bats is endowed, too remarkable and curious to be passed altogether unnoticed. The wings of these creatures consist, as we have seen, of a delicate and nearly naked membrane of vast amplitude considering the size of the body; but besides this, the nose is in some furnished with a membranous foliation, and in others the external membranous ears are enormously developed. Now these membranous tissues have their sensibility so high, that something like a new sense somehow accrues, as if in aid of that of sight. The modified impressions which the air in quiescence, or in motion, however slight, communicates; the tremulous jar of its currents, its temperature, the indescribable condition of such portions of air as are in contact with different bodies, are all apparently appreciated by the bat." So near, yet so far!


My website: http://www.plecotus.co.uk/
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Winter Bat Activity

We tend to think of winter as a time when bats hibernate and won't be seen again until spring. In fact hibernation is not as simple as that: bats do awaken at times and move around. Indeed, they are sometimes seen flying in the midst of winter.

This afternoon whilst walking the dogs I spotted a Pipistrelle foraging over the River Esk. It was flying round in circles in the clockwork flight pattern typical of the genus and occasionally dropping down to catch an insect. A feature of winter bat activity is that it happens in daytime, as the higher ambient temperature means there is a greater likelihood of catching enough insect prey to offset the energy costs involved in coming out of hibernation.

I tried unsuccessfully to interest the dogs in the bat, as I have an idea it could be rather useful to have a dog trained to listen for bat calls and alert me when there's a bat nearby. Unfortunately, my pair of canine delinquents find the command "sit" quite challenging, so they aren't likely to succeed in training as bat-dogs.


When I passed by later on at dusk the bat was still hard at work hunting and seemed to be having some success, despite the ambient temperature being only 3 or 4 degrees. I have heard several suggestions as to why bats occasionally feed during the winter. It may be that individuals have been forced out of hibernation because they have failed to build sufficient fat reserves to see them through the winter, but it seems more likely that fluctuations in temperature may cause individuals to take advantage of the opportunity to forage on insects which have become active.

Different bat species have differing requirements for hibernation. Here in Scotland Myotis species, such as Daubenton's (Myotis daubentonii) or Natterer's Bats (M. nattereri) seem to be particularly exacting, hibernating below ground in caves and mines which feature a steady, low temperature, low airflow and high humidity. They usually hibernate in crevices or ledges where the microclimate may be particularly stable.

Brown Long-eared Bats (Plecotus auritus) are less exacting. When found underground they tend to hibernate on walls or hanging from the roof and are often closer to mine entrances than the Myotids.

The least exacting bats are the Pipistrelles, which are rarely found underground, instead selecting relatively exposed holes and crevices, which are more likely to be influenced by changes in the weather. Whether there are differences between the two Pipistrelles is difficult to judge. As they are impossible to differentiate without handling, they tend to be lumped together in hibernation surveys.

Last winter I wrote about a castle where a group of Pipistrelles and a Brown Long-eared were hibernating in crevices within a cellar (See "Hibernating Pipistrelles", February 2008). The castle sits atop a hill and there is a constant breeze blowing through the cellar. Unsurprisingly, no Myotids were found hibernating there.

A hibernating Pipistrelle

Carol and Nigel Terry, our local bat carers noted that a casualty Pipistrelle kept through the winter in a cold room tended to wake up and feed every 10-14 days. It may be that Pipistrelle autecology makes use of winter foraging opportunities and that they choose hibernation sites which better allow them to respond to these opportunities.

My website: David Dodds Ecology

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Hibernating Pipistrelles

Today I spent a very pleasant couple of hours wandering through a semi-ruined castle with members of Lothians Bat group. We were there to look for hibernating bats, which occupy crevices and cracks in the decaying stonework. The most popular spot is in the deep, barrel-vaulted ceilings, which in other old buildings are often used for summer or autumn roosting.


To understand why they are so popular with bats, look at the schematic below. In a typical medieval building, arches and ceilings are built from stone blocks arranged into a curve, so that each is supported by the one outside of it. Above this, the infill is usually made of rubble. Over the years the mortar tends to fall out of the gaps between the stone blocks. As long misguided perfectionists don't repoint the stonework, this creates crevices, some of which may extend into spaces within the rubble fill, creating sometimes quite large bat havens. The downside for us is that surveying these buildings quickly causes a sore neck, from peering upwards, pointing a light into the crevices!


What is particularly interesting about the site we visited today is that, not only is it used by hibernating Brown Long-eared Bats (Plecotus auritus), two of which we saw, it is also used by Pipistrelles (Pipistrellus sp.). Remarkably little is known about the hibernating behaviour of Pipistrelle bats: they are rarely found in the mines and caves where larger British bat species are found hibernating. It is generally assumed that they hibernate individually in small crevices in trees or buildings and are probably more tolerant of fluctutations in temperature and humidity. So it was nice to find at least twelve of them here.

Unfortunately, it isn't possible to say whether they were Soprano Pipistrelles (Pipistrellus pygmaeus) or Common Pipistrelles (Pipistrellus pipistrellus): the physical distinctions are difficult enough with a bat in the hand! However, a braver bat-worker than I might note the dark muzzles and wonder if they might be commons.

Click on the picture below to see a larger version of it and you'll see the brown splodge in the centre resolve into a Pipistrelle's face.

The following two pictures show two groups of bats, sharing crevices. I have no idea how many are hiding behind the mortar in the first picture, but the crevice in the second contained seven bats.

My website: plecotus.co.uk

What's in a bat box?

Well, hopefully...bats.

When the first bat-box schemes were launched, in the 1970s, using sponsorship from viewers of BBC TV's "Nationwide" programme, there was one design: the standard wooden bat-box. They're not unlike a blue-tit nest-box, but instead of a hole on the front, the bats access by climbing a roughened board and entering through a narrow slit at the base. Easy and cheap to make from a single plank of rough timber, there must be many thousands of them around the country and they're as effective as ever.

Bat boxes do a great job of supporting bat conservation by raising awareness, providing an easy way of monitoring local bat populations, and by providing bats with roosting opportunities in places where alternatives are limited. Annual bat box occupancy checks carried out by local Bat Groups also give a great opportunity for novice bat-workers to see bats close up (strictly supervised by someone with an appropriate licence).

Today, many designs are available, to the extent that choosing bat-boxes is almost as hard as choosing a new car! Do we want it to emulate narrow crevices, to suit Pipistrelles, or bigger tree-holes, to suit Noctules? Do we want cheap and cheerful wooden construction, or shall we push out the boat and use deluxe woodcrete bat-boxes? How about a wedge shape? Should the door be on the top or at the front? Should it be painted black? And so on...

Here in the Lothians, a bat box containing anything other than Pipistrelles is sadly a rarity, though a box full of Pips is still a welcome sight. Whilst the traditional boxes are well-used, they seem to prefer slimmer, more crevice-like designs. However, the most popular design seems to be the dome-shaped woodcrete (a cement and sawdust mix) boxes, made by Schwegler. They're not cheap, but the occupancy rates are definitely higher.

Anyone thinking of putting up bat boxes would be well-advised to take advice from their local Bat Group. A little experience and foresight in choosing the right boxes and positioning them correctly will make a big difference to their success...or otherwise.

Advice from the Bat Conservation Trust: http://www.bats.org.uk/helpline/documents/Batboxes-yourquestionsanswered.pdf

My website: http://plecotus.co.uk/