Thursday, 24 April 2014

What’s not to like about bats?



Last week, I noticed Pipistrelle Bats (below) flying for the first time this year. It took me back to when our children were young and we used to stand on the patio at the rear of our house in Berkhamsted on summer evenings and watch Pipistrelles. We had the idea of counting how many there were, and where they were flying, but it was not possible to get accurate answers, such was the speedy flight of the bats, combined with their rapid changes of direction. They were clearly hunting over the garden (that contained a large pond at the time), so I would imagine that dancing midges and similar small insects were the diet on those evenings. We never did find out where they were roosting during the day, but it cannot have been far away.


While watching, we talked together about bat biology. We know that bat’s wings are formed by skin covering the extended finger bones and that flapping of the wings, and their orientation, is controlled by muscles that moved the arms and hands of their ancient ancestors. Anyone watching bats is aware that they are expert fliers and, although they have reasonably good eyesight, they use high-pitched pulses of sound for navigation and to locate prey organisms. I remember being able to hear the pulses when I was a child, but that was many years ago. Fortunately, we can all listen in on their high-pitched calls by using bat detectors that consist of an antenna coupled to a box containing equipment that makes the calls audible. I first came across these detectors when I was an undergraduate student and we went to a lake on campus to see how many different types of bats we could identify from their characteristic pattern of pulses. My next acquaintance with these detectors was many years later during a visit to Arlington Court in North Devon, where my wife and daughter joined me and a group of enthusiasts in seeking out bats on the estate. We walked in darkness and identified several species, being informed about each, and the use of their regular flight paths, by our guide. It was all fascinating, one’s sense of wonder being increased by the darkness, for there were no lights nearby (and it was matter of luck whether one stepped into a cow pat or two – we also remember that bit of our walk).


Arlington Court itself is an old mansion with a roost of Lesser Horseshoe Bats (above) that can be viewed by means of a video link. We were able to see offspring being suckled and then “hung up” by their mothers before the adults flew off to start hunting for insects. A visit to Arlington Court is highly recommended and it reminded us that these remarkable animals are mammals, just as we are. All this is an activity for spring, summer and autumn as, in temperate countries, many types of bats hibernate to overcome shortages of food insects and the cold temperatures of winter. 

Bats are animals with a range of sophisticated adaptations – flight, echolocation for navigation and feeding, roosting, hibernation – and all have evolved from earlier forms. Of course, if you are a Creationist you will have a different explanation and miss out on some fascinating theorising as to how such adaptations came about.

Unfortunately, not all people feel positive about bats. For many, they are associated with unpleasantness and they feature in many stories about witches – look at the illustrations that appear in shops during the commercialised festival of Halloween and you will see outlines of bats accompanying witches riding broomsticks. This association with the “dark world” stems from the crepuscular and nocturnal habits of bats, and our nervousness about what happens during darkness – a “fear of the night” and anxiety about the possible presence of evil spirits. There is also something about the rapid flight of bats that some find disturbing and one belief is that they can become entangled in hair. Professor Gary McCracken discusses folklore in interesting articles in BATS magazine 1,2 suggesting that the idea of bats becoming tangled in hair results from their flying close to the heads of people who act as swarm markers for insects like dancing midges. A further prominent feature of folklore is that bat blood, or other extracts from the animals, cure eye diseases; arising, no doubt, from the ability of bats to be active in darkness. This folklore is nonsense, of course, but some bats do feed on blood and these create a fear that has been associated with many other bats that do not have this habit.


There are three types of Vampire Bat and one feeds on mammal blood, while the other two predominantly attack birds. They all have very sharp teeth that produce a wound from which blood is lapped up by the tongue, flow being maintained by the use of anticoagulants in the saliva. Vampire Bats, and their habits, have entered popular culture in the writings of Natural Historians like Charles Waterton, whose books were read avidly in the Nineteenth Century and his descriptions of Vampire Bats were repeated, without qualification, in the chapter Edith Sitwell devoted to Waterton in her well-known book The English Eccentrics. 3 The following extracts come from Waterton’s Wanderings in South America and appear in his Third and Fourth Journeys:

As there was a free entrance and exit to the vampire in the loft where I slept, I had many a fine opportunity of paying attention to this nocturnal surgeon. He did not always live on blood. When the moon shone bright, and the fruit of the banana tree was ripe, I could see him approach and eat it. He would also bring into the loft, from the forest, a green round fruit, something like the wild guava, and about the size of a nutmeg.. ..The vampire, in general, measures about twenty-six inches from wing to wing extended, though I once killed one which measured thirty-two inches.. ..I had often wished to have been once sucked by the vampire, in order that I might have it in my power to say it had really happened to me. There can be no pain in the operation, for the patient is always asleep when the vampire is sucking him; and as for the loss of a few ounces of blood, that would be a trifle in the long run. Many a night have I slept with my foot out of the hammock to tempt this winged surgeon, expecting that he would be there, but it was all in vain; the vampire never sucked me and I could never account for his not doing so, for we were inhabitants of the same loft for months together. 4

The teeth of the vampire are very sharp, and not like those of the rat. If it be that he inflicts the wounds with his teeth (and he seems to have no other instruments) one would suppose that the acuteness of the pain would cause the person who is sucked to awake. We are in darkness in this matter, and I know of no means by which one might be enabled to throw light upon it. It is to be hoped that some future wanderer through the wilds of Guiana will be more fortunate than I have been, and catch this nocturnal depredator in the act. 5

The descriptions of feeding by Vampire Bats are accurate and Waterton was impressed by the action of the anticoagulants, although he had no knowledge of their existence. He was also correct in stating that Vampire Bats often feed barely noticed by their “victims” and their success in being able to feed freely is impressive. However, it is no surprise that Charles Waterton was not attacked by the bats from his loft. From his description, it is clear that these were Fruit Bats, as Vampire Bats feed exclusively on blood and are smaller than Waterton's co-habitants.


The more one looks at bats, the more one is amazed at their adaptations. They vary in size from Pipistrelles to large Fruit Bats and yet all have the same basic biology, with a very successful body plan and physiology. It is a pity that some people view them with a quite unnecessary sense of fear.





3 Edith Sitwell (1933) The English Eccentrics. London, Faber and Faber.

4 Charles Waterton (1891) Wanderings in South America: Third Journey. London, Thomas Nelson and Sons [combined edition].

5 Charles Waterton (1891) Wanderings in South America: Fourth Journey. London, Thomas Nelson and Sons [combined edition].



Friday, 11 April 2014

Putti and bumblebees



I was delighted to give the 15th Annual Robert Grant Lecture on the topic Zoology and mythology: looking at angels, fairies and dragons. Using a superficially light-hearted approach, I examined the form and function of these three types of creatures from a zoologist’s perspective, asking such questions as: What type of wings did each creature have? How were the wings anchored in the skeleton? How were the wings flapped (if they were flapped)? How were the flight muscles located in the body? The lecture, while based on serious anatomical principles, was really an investigation of the way we accept images showing angels with bird wings; fairies with insect wings; and dragons with wings like those of bats. It was a theme I had developed in an earlier essay, 1 where I also discussed putti, such a feature of Italian Renaissance art. These human infants have tiny bird wings that enable them to fly above the subject(s) shown in paintings, gather on the ground near them, or look down from a high point in a room or building. To save time, I omitted putti from the Grant Lecture and I’d like to return to them now in a comparison with bumblebees; animals that also have small wings for the size of their bodies.



Bumblebees only fly when their flight muscles are sufficiently warmed up and, on cold mornings, this is achieved by “sunbathing” and, importantly, by vibrating the flight muscles without flapping the wings. 2 This is possible because the muscles used to power flapping flight are not attached to the wing, but to the walls of the thorax, as is typical in advanced insects. I am not going to give details of the flight mechanism here and, if you are puzzled by the idea of indirect flight muscles, you will be astonished by the role played by muscles and skeletal structures that allow the wings to be rotated and moved forwards and backwards, all these being needed to generate lift and propulsion.

We know much of the flight mechanism of insects as we can study it directly and also make many measurements using sophisticated contemporary techniques. It is only possible to speculate on how putti fly, although their naked, often chubby bodies indicate that the generation of sufficient temperature is not a problem. However, the size of their wings means that large volumes of air need to be displaced rapidly and this can only be achieved by exceedingly rapid wing beats. So rapid that the tip of the wing will move at supersonic speed and feathers would likely be ripped to pieces. We must conclude therefore that putti, like angels, fairies and dragons cannot fly using their wings and that the images we have of these creatures are inventions. However, I was surprised to find this image when searching on the internet:


Was this the wing of a putto mounted on a tailor’s dummy, complete with wiring involved in the flight mechanism? I hope you will excuse my little piece of fun in asking this question as this is indeed a bird wing, but used in the unique jewellery of Julia de Ville (http://www.juliadeville.com).

So, why did I write this blog post? Partly because I enjoy whimsy and hope that readers do too, and partly to highlight that we can believe some very strange things about the appearance of angels, fairies, dragons - and even putti. We do this while largely ignoring the astonishing variety of form and function of the real creatures that are all around us. Just looking at bumblebee flight fills one with amazement at what has occurred in the evolution of these insects, without even considering their mouthparts, vision, sense organs, and many other aspects of their biology. It fills one with awe, whether one is an atheist or of religious persuasion


Wednesday, 2 April 2014

Looking at the countryside from railway carriages



In the Preface of A Naturalist’s Rambles on the Devonshire Coast, the Victorian Natural Historian Philip Henry Gosse wrote: 1

..I have not made a book of systematic zoology; nor a book of mere zoology of any sort. I venture to ask your companionship, courteous reader, in my Rambles over field and down in the fresh dewy morning; I ask you to listen with me to the carol of the lark, and the hum of the wild bee; I ask you to stand with me at the edge of the precipice and mark the glories of the setting sun; to watch with me the mantling tide as it rolls inward, and roars among the hollow caves; I ask you to share with me the delightful emotions which the contemplation of unbounded beauty and beneficence ever calls up in the cultivated mind.

This is typical both of Henry Gosse’s writing style and his approach to Natural History. In A Naturalist’s Rambles on the Devonshire Coast he gives detailed descriptions of many marine organisms, but always in the wider context of habitat and environment.

One of the pleasures of studying Natural History is that it allows us to appreciate the huge variety of living things at scales from the microscopic to that of landscapes. Although one cannot see the creatures in a pond, one knows the types that are likely to live there, their habits and biology. Added to that is an understanding of how the pond ecosystem functions, with the energy from organic matter passing through micro-organisms, to plants and animals of all sizes. In the same way, background knowledge enhances one’s appreciation of coasts, woods, hedgerows or any other natural features of the landscape, whether one is observing on foot or using some form of transport.

 
                    [Acrylic painting by Anna Todd in the collection of the Cardiff and Vale University Health Board]

I have always enjoyed travelling by train and my journeys are rarely spent reading or chatting, although the former was my chosen approach during years of commuting to work in London. For me, railway journeys have always been an opportunity to gaze out of the carriage window and observe the countryside we passed through. I’ve always found that the best view is provided when travelling First Class and that, perhaps, results from well-placed seats and large windows that give a wide field of vision. To make it affordable, travelling First Class now requires advance booking and gone are the days when trains were made up of miscellaneous carriages some of which had First Class compartments labelled as being available for the use of Second Class passengers (see the sticker below). It was always worth scanning along the carriages of those trains to see if one’s luck was in.


Henry Gosse preferred to travel First Class on trains 2 and, in his time, during the expansion of the railways, this would have been an expensive option. It is not recorded whether he used to gaze from the window, but I’m sure that he did, especially as he was naturally shy, although his occasional outbursts of religious evangelism also had the unintentional effect of buying the silence of other passengers. As the brilliant biographer Ann Thwaite wrote of a journey he made with his son, Edmund: 2

They travelled first class, as Henry always did. At Newton Abbot a young woman joined them and a label on her luggage announced her to be ‘Miss Christabel Coleridge’. Edmund was consumed with curiosity, wondering if ‘she was of the poet’s family’. No one spoke a word and she got out at Exeter, where her place was taken by an elderly gentleman. The two men started talking and the boy found himself listening to the sort of conversation he had heard so many times as a small boy travelling with his mother. Now his feelings were different. Without much preliminary, Henry Gosse ‘advanced the Cross of Christ. He eagerly enquired whether our new acquaintance had found peace on the bosom of his Saviour’. The answer was curt. The elderly gentleman withdrew to his corner of the carriage, buried himself in a book and took no further notice of them.

It is not surprising that there was no communication with ‘Miss Coleridge’ on this journey, as the railway line between Newton Abbot and Exeter passes right along the coast and then up the muddy Exe estuary and it is a brilliant stretch for a Natural Historian to make observations of wildlife. Trains in Gosse’s time moved more slowly than those of today, but their sudden and noisy appearance was sure to disturb many birds and other animals and that made them easier to see.

As a boy, I used to enjoy travelling on the branch lines of Devonshire using Holiday Runabout tickets that allowed unlimited travel for a week on all lines within a defined area. As I lived by the sea, I headed for the country and also stopped off to look at some of the small towns and villages that I had not visited previously. Trains on branch lines moved at a gentle pace and one thus felt more integrated with the landscape and the “rural idyll”. There was always much to see on these train journeys, but this pleasure cannot be enjoyed nearly as much today, for most of the lines are now closed, although some track beds remain as cycle tracks. I empathise with the sentiments made by John Betjeman in a BBC Radio broadcast of 10th March 1940, a time when the peaceful country railways must have seemed havens from bad news: 3

Roads are determined by boundaries of estates and by villages and other roads; they are shut in by hedges, peppered with new villas, garish with tin signs, noisy with roadhouses. A town spreads out along its roads for miles, leaving the country in the fields at the back that you don’t see.. ..railways are built regardless of natural boundaries and from the height of an embankment we can see the country undisturbed, as one who walks along an open footpath through a field.. ..Railways were built to look from and look at. They still provide those pleasures for the eye.. ..I advise slow trains on branch lines, half-empty trains that go though meadows in the evening and stop at each once oil-lit halt. Time and war slip away and you are lost in the heart of England.

I know what he means and I’m grateful to have had what are now nostalgic memories of branch line travel in the 1960s. My interest in Natural History enhanced those trips, just as it does when enjoying modern train travel. In the most pleasant sense, there is no escape from having a knowledge of Nature.





1 Philip Henry Gosse (1853) A Naturalist’s Rambles on the Devonshire Coast. London, John Van Voorst.

2 Ann Thwaite (1984) Edmund Gosse: A Literary Landscape. London, Secker and Warburg

3 John Betjeman (2006) Trains and Buttered Toast. London, John Murray.