Bird Migration

A Birds are highly mobile and among the swiftest of living creatures. Flight gives them the power to move in any direction for as long as they have the energy to keep going. They are equipped with lightweight, hollow bones, a finely-tuned navigation system and an ingenious heat-conserving design that allows them to face life in the harshest of climates. Their respiratory systems have to perform efficiently during sustained flights at altitude, so they have evolved a system of extracting air from their lungs that far exceeds that of any other animal. These features enable birds to come and go with the seasons. On the way, they face constant danger and a daily requirement to find food, water and a safe place to rest. So why do millions of birds migrate rather than stay in one place?

B Most of the explanation revolves around food. In temperate and arctic regions of the northern hemisphere, food is abundant during a short growing season. Migration evolved as a way for birds to exploit resources that are seasonally abundant and, equally important, to go elsewhere when the resources become scarce or harsh weather arrives. Many species can tolerate cold temperatures if food is plentiful but when food is not available they must migrate.

C While this simple explanation for why birds migrate is essentially true, intriguing questions remain. One puzzling fact is that many birds journey much further than would be necessary to find food and good weather. Another apparent conundrum involves the huge migrations performed by arctic birds and mudflat-probing shore birds that breed close to polar regions. In general, the further north a migrant species breeds, the further south it spends the winter. Yet, en route to a final destination in southern latitudes, all these individuals overfly areas of seemingly suitable habitat spanning two hemispheres. Such compulsive journeys probably evolved over time and in response to fluctuations in weather but we do not really know.

D But just how do birds reach their destination and, more to the point, how do young birds migrate over vast distances without parental assistance? Very few adults migrate accompanied by their offspring and youngsters may have little or no inkling of their parents’ appearance. Cuckoos are famous for depositing their eggs in the nests of other birds that unwittingly serve as foster-parents. Astonishing as this piece of evolutionary behaviour is, it is even more remarkable to consider that, once grown, the young cuckoo makes its own way to ancestral wintering grounds in the tropics before returning single-handedly to northern Europe to seek out a mate among its own kind.

E As we continue to study bird migration, its mystery is better understood but also compounded. Mounting evidence has confirmed that birds use the sun and stars to obtain compass directions but true navigation requires an awareness of position and time, especially when lost. Experiments have shown that, after being taken thousands of miles over an unfamiliar landmass, birds are still capable of returning rapidly to nest sites. Such phenomenal powers are the product of computing a number of sophisticated cues including an innate map of the night sky and the pull of the Earth’s magnetic field. How the birds use their ‘instruments’ remains unknown, but one thing is clear -- they see the world with a sensory perception superior to ours. Most small birds migrate at night and take their direction from the position of the setting sun. However, as well as seeing the sun go down, they also seem to see the plane of polarised light it causes. This calibrates their compass. Travelling at night provides other benefits: the danger of meeting predators as well as the risk of dehydration due to flying for long periods in warm sunlit skies is reduced. Furthermore, at night the air structure is cool and smooth and conducive to sustained, stable flight.

F Nevertheless, all journeys involve considerable risk and part of the skill in arriving safely is setting off at the right time. This means accurate weather forecasting and utilising favourable winds. Birds are adept at both and, in tests, some can detect the minute difference in barometric pressure between the floor and ceiling of a room. Often birds react to weather changes before there is any visible sign of them. Certain species that feed on grassland flee at the onset of a cold snap because when the ground surface freezes the birds could starve. Yet they return ahead of a thaw, their arrival linked to a pressure change presaging an improvement in the weather.

G Unfortunately, some never complete their journey. Not so long ago the assumption was that a bird in the air on a dark windy night with no visible reference points to judge position was like a pilot without radar, hopelessly lost. We now know this is not the case. Losses do occur, but mainly because birds get swept off course by strong air masses against which battle is futile, and this results in a watery grave. Indeed, it is not unusual for ocean fish to be caught with bird remains in their stomachs. But sometimes there’s a silver lining. Each autumn a small number of North American birds are blown across the Atlantic by fast-moving westerly tail winds. Not only do they arrive safely in Europe but, based on tracking evidence, some make it back to North America in the following spring -- probably after spending the winter with European migrants in sunny African climes.

On Art and Artists

A There really is no such thing as art, only artists. Once these were people who took coloured earth and roughed out the forms of a bison on the wall of a cave; today some buy their paints, and others design posters for hoardings; they did and do many other things. There is no harm in calling all these activities art as long as we keep in mind that such a word may mean very different things in different times and places, and as long as we realize that ‘Art’ with a capital ‘A’ has no existence: it has become something of an obsession. You may crush an artist by telling him that what he has just done may be quite good in its own way, only it is not true art.

B Actually, I do not think that there are any wrong reasons for liking a statue or a picture. We may like a painting of a village scene because it reminds us of home. There is nothing wrong with that. All of us, when we see a painting, are bound to be reminded of a hundred-and-one things which influence our likes and dislikes. As long as these memories help us to enjoy what we see, we need not worry.

C It is only when some irrelevant memory makes us prejudiced, when we instinctively turn away from a magnificent picture of an alpine scene because we dislike climbing, that we should search our mind for the reason for the aversion which spoils a pleasure we might otherwise have had. There are wrong reasons for disliking a work of art.

D Most people like to see in pictures what they would also like to see in reality. This is quite a natural preference. We all like beauty in nature, and are grateful to the artists who have preserved it in their works. Nor would these artists themselves have rebuffed us for our taste. When the great Flemish painter Rubens made a drawing of his young son, he was surely proud of his good looks, and wanted us, too, to delight in the child’s appearance. But this bias for the pretty and engaging subject is apt to become a stumbling block if it leads us to reject works which represent a less appealing subject.

E The great German painter Dürer certainly drew his mother with as much devotion and love as Rubens felt for his child. His truthful study of old age may give us a shock which makes us turn away from it -- and yet, if we fight against that first reaction we may be richly rewarded. For Dürer’s drawing in its tremendous sincerity is a great work. The beauty of a picture does not really lie in the beauty of its subject matter. The trouble about beauty is that tastes and standards of what is beautiful vary so much.

F What is true of beauty is also true of facial expression. In fact, it is often the expression of a figure in the painting which makes us like or loathe the work. Some people like an expression -- perhaps of suffering or of compassion -- which they can readily understand, and which therefore moves them profoundly. But we should not, for that reason, turn away from works whose expression is perhaps less easy to understand. Often we must first learn to know the artist’s methods of drawing to understand the feelings he or she wishes to portray, and may even come to prefer works of art in which expression is not obvious. Just as some of us would rather people use few words and gestures and leave something to be guessed, so some of us would rather look at paintings or sculptures which are open to interpretation.

G But here newcomers to art are often brought up against another difficulty. They want to admire the artist’s skill in representing the things they see. What they like best are paintings which ‘look real’. This is an important consideration, and the patience and skill which go into the faithful rendering of the visible world are indeed to be admired. Great artists of the past have devoted much labour to works in which every tiny detail is carefully recorded. Dürer’s watercolour study of a hare is one of the most famous examples of this loving patience. But who would say that Rembrandt’s drawing of an elephant is necessarily less good because it shows fewer details? Indeed, Rembrandt gave us the feel of the elephant’s wrinkly skin with just a few lines of his chalk.

H If we find fault with the accuracy of a picture, we must remember that artists may have their reasons for changing the appearance of what they see. We should also never condemn a work for being incorrectly drawn unless we are quite sure that we are right and the painter is wrong. We have a curious habit of thinking that nature must always look like the pictures we are accustomed to. For generations, paintings showed horses galloping with outstretched legs in full flight through the air, and we came to believe that this was indeed how they moved. It was only the development of photography which proved that horses simply do not gallop in that way. And yet, when painters began to apply this new discovery, and painted horses moving as they actually do, everyone complained that their pictures looked wrong.