TEN

The Limits of Endurance

No other group of backboned animals has colonised the earth as extensively as birds have done. Amphibians, with their moist skins, must remain within reach of water. Reptiles have escaped from that restriction and most have become entirely terrestrial, but lacking the ability to generate their own body heat internally, they cannot survive in regions that are permanently cold. Mammals, with their warm blood and insulating fur, have succeeded in making their homes amid snow and ice and a few have even taken to the seas. But they too have their limitations. They cannot, unaided, colonise remote oceanic islands. Such specks of land, fertile and rich in food though they might be, were even beyond the reach of human beings until the invention of sea-going craft a few millennia ago. Birds, however, have long since broken all these barriers and reached all these places. They can tolerate the most extreme cold for their body temperature is permanently high, excellently controlled and efficiently conserved by their plumage. Some are superlative swimmers and divers, capable of descending to depths of 300 metres, and with their mastery of the air, they can reach the most distant island and ascend towards the very frontier of the earth’s atmosphere.

But there is one element that neither birds nor any other animal can do without: liquid water. Deprived of that, their bodies can neither digest their food, circulate the nourishment they derive from it, nor get rid of the poisonous waste it generates. Some, such as eaters of fish or fruit, manage to extract all the water they need from their diet, but in dry environments the food birds find is inevitably poor in liquid. For them, water is an imperative and its absence a major limitation.

The deserts of Africa and the Middle East exist over great areas so dry that they have no permanent vegetation whatsoever. There is nothing but scorched rock, pavements of wind-polished pebbles and huge dunes of sand. Rain does occasionally fall, but it is very infrequent and sporadic. When it arrives, however, the desert, almost miraculously, springs to life. Seeds that have lain dormant in the sand maybe for decades suddenly germinate. The tiny shoots grow rapidly. They flower within a week or so, but with no more rain to sustain them, they wither and die. By then, however, they have released thousands of seeds which in many species are as fine as dust. And it is these that constitute the main food of sandgrouse.

Sandgrouse are not grouse at all, but distant relatives of the pigeons which they resemble both in size and general shape. The seeds they live on are so tiny that each bird has to collect some eight thousand a day if it is to be reasonably well fed and even that huge number does not weigh, collectively, more than about a gram and a half. They collect them with rapid stabs of their beak. Working like manic sewing machines, they move over the sands, picking up several seeds a second. The seeds, however, are very dry and cannot supply the sandgrouse with the moisture they must have, so every two or three days, the birds must stop eating and find a drink. If the weather is particularly hot, they may need to do that once a day. Waterholes are few, but the birds will fly as far as 80 kilometres to visit one.

The patchy nature of rains in the desert and therefore of its seeds means that in many deserts sandgrouse can have no settled homes or territory. They are permanent nomads, wandering across the sands and nesting, when the time comes, wherever they may happen to be. They lay their eggs, usually in a clutch of three, in a shallow scrape in the sand. As soon as they hatch, the chicks leave the nest and start collecting seeds for themselves. But they too must drink – and they cannot fly. Water must be brought to them and it is the male that takes on the task.

Parent birds of some species ferry water to their young by carrying it in their crops, but the male sandgrouse needs all the water he can accommodate in his crop for his own survival on such long journeys. He does, however, have another and unique way of carrying it. The feathers of his breast and underside are covered on their inner surface with a mat of fine filaments. When he arrives at a waterhole, he rubs his underside in the sand and dust, so removing any water-repellent preen oil there may be on those feathers. Then he moves to the water’s edge. First he slakes his own thirst, sucking in water and lifting his head to gulp it down. Then he wades into the water, lifting his wings and tail to keep them clear of it, and begins to rock his body to and fro so that his belly feathers get thoroughly soaked. The mats of filaments on them absorb water like a sponge. He may stay in the water, no doubt luxuriating in its delicious coolness, for several minutes, but usually the huge numbers of other sandgrouse flying in from all over the desert for their daily drink create such a press at the water’s edge that he cannot hold his place for long and he takes off.

His liquid cargo, held between his feathers and his body, is well protected against evaporation, but even so most of it will have gone if he has to fly much more than 30 kilometres. When at last he lands near his chicks, which are scattered over the sands searching for seeds, they run to him. He lifts his body high and they extract the liquid from his belly feathers like mammalian babies suckling milk. His load delivered for the day, he walks away and dries himself by once again rubbing his belly in the sand. He performs this service every day for at least the next two months until his chicks have completed their first moult and can fly and collect water for themselves.

Finding water might not seem to be a problem for those birds that live in the Rift Valley of eastern Africa since lakes lie along its length. But these lakes are not like others. The streams that in the rainy season drain down the sides of the Rift and flow into the lakes dissolve salts from the volcanic ash and lava over which they pass. As the lake water heats in the baking sun, so it evaporates and the salt content rises, with the result that most of these lakes are now much more briny than the sea. But one of them is so heavily saturated that around its margins the salt is solid. This is Lake Magadi. It is different because it acquires its salt not only from streams but from underground. The titanic forces, deep within the earth, that are pulling Africa apart, creating the Rift, have also caused lines of faults along its margins and across its floor. Several volcanoes rise from them as do hot springs which bubble up through the floor of the Rift. One of them feeds Lake Magadi. As the superheated water is forced up through the rocks, it dissolves sulphates and carbonates. When it reaches the surface and cools, these salts solidify and form white curds that glint and shimmer in the sun. It must seem like some cruel joke to a weary traveller approaching the lake on foot and tortured by thirst, that the water ahead should appear to be covered by ice. When he reaches it, he finds that the curds and plates covering the mud around its edges are so caustic that they will burn the skin from his flesh and if he tries to drink the tepid stinking liquid beyond, he will retch.

Flamingos feed on all of the salt lakes of the Rift at various times, and share the food in and around them with several other species of birds, but few except flamingos can tolerate the conditions at Magadi. Fish cannot survive in its waters except near some springs at the southern end where the newly erupted water is very hot but slightly less salty.

Algae and brine shrimp, however, can do so, and because so few other organisms can survive in these conditions and compete with them, they proliferate in vast quantities. And they, in turn, are food for flamingos. Two species are here: the greater flamingo, which stands nearly 1.5 metres high, and the lesser, which is half the size and constitutes the overwhelming majority. Both have webbed feet which spread their weight and enable them to walk over mud without sinking too deeply into it. Their legs and feet are scaly and not affected by the caustic salts. The greater flamingo collects shrimps and worms by plunging its head and often most of its neck deep in the water and walking forward, ploughing through the mud. But it is the lesser flamingo that has become the most extremely specialised for life in this forbidding environment.

It lives predominantly on the blue-green algae. These microscopic plants float in the upper surface of the water and the lesser flamingo collects them with one of the most complex beaks possessed by any bird. When feeding, it lowers its long neck and holds this beak, upside down and pointing backwards, just beneath the surface of the water where the algae it seeks congregate. The lower mandible is bulbous and has a honeycomb of air-filled spaces which cause it to float, so minimising the muscular effort needed to hold the beak in the right place in the water. The bend in the middle of the beak, that gives the flamingo its equivalent of a Roman nose, is of particular importance. Were the beak to be straight, then when it opens, the gap between the mandibles would steadily increase from the corner of the gape to its tip. With a bend in the middle, the flamingo is able to separate its mandibles just slightly so that the distance between them is almost the same along nearly all of its length. There is therefore no danger of a feeding bird taking in larger objects than it wants. Internally, the edges of the mandibles are lined by hinged horny plates. The bird’s tongue acts as a pump, moving extremely rapidly backwards and forwards. As the tongue retracts, the hair-covered plates are swept down flat and water is drawn in. As the tongue pushes forward again, the plates lift, water is expelled and the algae and shrimp are strained off by the hairs. Backward-pointing spines on the palate and the tongue guide the food particles into the throat. The bird is thus able to swallow its food with the minimum of salty water. Pumping in mouthfuls twenty times a second, a lesser flamingo can filter twenty litres of water a day and extract from it sixty grams of food.

As the dry season approaches, the heat intensifies. The water level of the lake begins to drop and the birds’ feeding grounds shrink. Worse, land predators such as jackals, hyenas or even lions, can now reach them. The flock’s behaviour changes. They begin the preliminaries of courtship, forming platoons and marching past one another with parade-ground precision, flicking their heads from side to side. They salute one another by flashing open their wings to reveal their red coloration which is there at its most intense. And then suddenly, overnight, the whole flock disappears. This does not happen every year. Nor is it possible to predict with accuracy exactly when in any year it will do so. But the birds have gone away to breed. The same thing will be happening simultaneously at all the other salt lakes in the Rift.

Where the flamingos go was, for many years, a mystery. Only in 1954 was it discovered that they flew to the most savage and, to human eyes, the most forbidding lake of all, Lake Natron. Like Magadi, it is fed with salt from subterranean sources which solidifies around its margins, but it is many times bigger, being 23 kilometres wide and 56 kilometres long. The algae it contains flourish in such quantities that they stain the soda pink. Now, in the dry season, it gets so hot that surface temperatures reach 60 °C. It is so big that the mudflats in its centre are, at this time, beyond the reach of land predators.

Three million pairs of flamingos assemble in an immense flock in a shallow area so far from the shore that they are almost out of sight. Here they build mounds of mud with a shallow depression on top in which they lay their single egg. The nests have to be sufficiently tall to keep the egg above any spray that the wind might blow up from the surface of the water. If that caked the egg with salt, the chick within would suffocate. The parents feed the chicks as pigeons do, with a milky secretion which they produce from their throats and drip into the chick’s uplifted bill. As the dry season advances and the water level continues to fall, it becomes possible for a jackal or some other predator to splash through the shallows and reach the nests. By now, however, the chicks are strong enough to walk. Soon they begin to leave the nesting flats, marching in long columns across the salt to look for deeper water where they might find food for themselves. The journey may be a long one. In years when the rainfall is low, the shallows through which they trudge are only a few inches deep and the water has become so saturated with salt that it solidifies and forms hard rings around their legs. The weight of these anklets becomes so great that eventually, many chicks become exhausted and collapse and die on the salt. In such years, whole generations of chicks are lost. That is one of the penalties of colonising one of the hottest places on earth.

The coldest places on earth lie in Antarctica. Penguins standing on ice floes have become the very symbol of frigidity. In fact, more than half of the eighteen species in the family live in gentler climates where they seldom if ever see ice – in Australia, South Africa, the shores of Peru and even on the equator in the Galapagos. Some, however, endure very bleak conditions indeed. The island of South Georgia lies just outside the Antarctic Circle, so it does not totally lose sight of the sun even in midwinter. Nonetheless its jagged mountains are cloaked in great glaciers which sweep down into the sea and raging gales raise huge seas which crash into its coast. In winter, snow drifts 2 metres deep cover its slopes and the temperature falls to -15 °C. Macaroni penguins arrive on this inhospitable island in mid-October, the southern spring, and assemble in vast colonies two hundred thousand strong. The males come first and claim a territory. The females follow a few days later, and after twelve days or so on land, begin to lay. Male and female take turns incubating the eggs in ten-day shifts and after a little more than a month, the eggs hatch. Now both adults work assiduously bringing food to their young. Sixty days after hatching, in mid-February, the young have moulted their down and acquired their sea-going plumage. The whole process has taken just four months and has been completed before winter returns.

King penguins breed on the island too. They are much larger birds, standing a good 23 centimetres taller than macaronis. That being so, their chicks need a longer time to grow to full size. Some adults arrive in November, but they take three weeks longer than the macaronis to incubate their eggs which are twice as big, and by the end of the summer, when the full-grown macaroni young are leaving, the young king penguins, although they have reached adult weight, are still not strong enough to go to sea and are still clad in overcoats of thick furry brown down. They stand around in creches several hundred strong. Their parents come back regularly to feed them, each identifying its own offspring among the crowd by the sound of its call. But as summer moves into winter, the days darken, the temperature of the sea falls, and the shoals of the shrimp-like krill, the kings’ dietary mainstay, begin to disperse. So food becomes much harder for the adults to find. Their visits to feed their young, perforce, become more infrequent and eventually cease. As winter sets in, the chicks start a long fast. Those that hatched late in the season – and some may have done so as late as mid-April – stand no chance of survival. Hundreds in the colony die.

The following spring the parents return and rejoin the survivors. Feeding is resumed and in the summer when the chicks are between fourteen and sixteen months old, they moult their down and swim away from the island. It is too late now for their parents to lay again, so they too leave the island and travel to their feeding grounds to regain their strength. As a consequence of this timetable, king penguins can only breed successfully once every two years.

Farther south, on the coast of the Antarctic continent, the summer is, of course, even shorter and the winter even more bitter. King penguins do not breed here, but their cousins, the emperors do. These birds weigh twice as much as kings. This may, in itself, be an adaptation against the cold. A body can only lose heat from its surface. The bigger an animal is, the smaller its surface in proportion to its volume. So a big body retains heat more efficiently than a smaller one of the same shape. But when it comes to breeding, this bigger size, together with an even shorter summer, presents the emperors with an even greater problem.

They solve it by adopting a strategy that involves the most extreme hardship endured by any warm-blooded animal – mammal or bird. Instead of starting their breeding cycle at the beginning of the Antarctic summer, they do so at the very end. At this time, March or early April, the fringe of ice that surrounds the Antarctic continent like a white collar is at its narrowest. The emperors land on its edge, shooting out of the sea like rockets, and then travel south across it, sometimes waddling upright, sometimes lying on their bellies and pushing themselves forward with their flippers, towards the land which is still likely to be several kilometres away. They never reach it. Eventually, they come to a patch of permanent ice that is likely to have served them as a breeding ground for many years. As many as twenty-five thousand may gather in one enormous crowd and here they begin to court. The male stands still, drops his head on his chest, takes a deep breath and lets out a series of trumpeting hoots. These calls, repeated many times over days, eventually attract a female. The pair face one another, point their beaks towards the sky and stand there motionless for several minutes. They have become a pair. Thereafter the two waddle around together until the moment for copulation arrives. One of them points its head downwards; the other does likewise. Then they mate.

By now winter is approaching fast. The temperature is falling rapidly and the ice around the continent is extending outwards by 3 kilometres a day. In May or early June, the female produces one large egg. The pair have made no attempt to make a nest for there is nothing with which to make it – except snow. She cannot leave her egg on the ice, for it would freeze. Instead, she places it on the top of her feet. Within hours, the male walks up to her and the two stand facing one another, breast to breast. He endeavours to take the egg from her, prodding at it with his toes. Often she is reluctant to surrender it, but eventually she lets it slide on to the ice. Within seconds, the male gets his toes beneath it, juggles it up on to the top of his feet and covers it with a fold of his densely feathered abdomen. Producing the egg has taken a significant proportion of the female’s bodily reserves. She needs urgently to replenish them and she heads back to the sea.

The male is now entirely responsible for incubating the egg. He stands with his companions occasionally shuffling forwards for a few metres. But there is nowhere to go. Penguins of other species become exceedingly quarrelsome when they are incubating but the male emperors cannot afford to be. As the winter winds begin to blow, the days darken, the temperatures fall, and the emperors huddle closer and closer together. They use their tiny stump of a tail as the third leg of a tripod and rest on their heels, with their toes inclined upwards keeping their precious eggs off the ice and snug within the brood pouch, where it is 80 °C warmer than outside. The blizzards increase in severity, the wind screams across the ice at 200 kilometres an hour and the males huddle still closer, their beaks drawn down to their chests so that the napes of their necks, pressed tightly together, form a feathered roof with scarcely a gap between them. Those on the side facing the wind take the full brunt of its force. But not for long. They shuffle around the sides of the huddle and shelter in its lee, so there is a constant movement. They have nothing to eat. Midwinter comes and for a month there is total darkness, except for the shifting veils and curtains of the Southern Lights playing overhead.

After sixty days, the eggs hatch. The males, now close to starvation, manage to produce a little milky secretion from their gullets for their chicks. And at this critical moment, the females reappear. They have been travelling across the ice for a long time, for since they came here to lay at the end of summer, the ice fringe around the continent has extended very considerably. Some may have had to walk a hundred kilometres. They exchange calls with their mates, the two recognising the sounds they learned during courtship, even after their three months of separation. The females have full crops and bend down to regurgitate their little chick’s first real meal. One might think that the males would be only too anxious to leave, but they seem reluctant to relinquish their young and most continue to brood for about ten days. Then they start the long trek back to the sea to take their first meal for almost four months.

Three or four weeks later, they are back and take over care of the chicks, allowing the females to return to the sea. The chicks at this early stage in their lives have not yet developed the ability to generate their own heat. If they were left unprotected on the ice, they would die within two minutes. Their parents take turns in fetching food and guarding them, but even so one in four chicks die within the first month. As winter slackens its grip and the sea ice begins to break up again, the journey from the breeding grounds to the sea gets shorter and the parents are able to increase the frequency of feeding. The chicks gather into their own huddles. By early November, they are beginning to lose their downy coats and a hundred and fifty days after hatching, they start to fledge. The parents now stop feeding them and all, in long processions, trail down to the sea and food.

No one knows how long it took for individuals of one branch of the ancestral king penguin family to grow a little in stature, change their nesting regime and so become emperors and succeed in colonising the ice fringe of Antarctica. Birds are, however, surprisingly swift to change their behaviour in order to extend their range and get the best out of new circumstances. A hundred and fifty years or so ago, a completely new kind of environment began to appear. Mankind started to build not only with relatively friendly stone or brick but with glass and metal. The streets between these new buildings were no longer covered with mud but sealed from the earth by layers of concrete and asphalt, and the vehicles that carried people and goods along them were not powered by horses, whose droppings had provided ample meals for many birds in the past, but by internal combustion engines which pumped out poisonous gases. Over vast areas, there was not a green leaf to be seen. The daily rhythm of light and dark was disrupted by blazing artificial lights that turned night into day. A more alien environment could hardly be imagined. Yet birds colonised it almost immediately.

In spite of the fact that virtually nothing edible grows in these new-style cities, they contain abundant food, for their human inhabitants are very wasteful. This refuse is not allowed to accumulate around their dwellings. Fleets of lorries tour the streets, collecting it and taking it away to dumps beyond the cities’ outskirts. There great earth-moving machines roar back and forth, levelling the loads dumped by continuous processions of lorries. The air is heavy with the stench of decay. Tatters of plastic wrapping, which neither rot nor fragment, blow about in drifts and hang from snags and spikes like travesties of leaves. Smoke swirls from innumerable small fires. But mixed with the poisonous chemicals, the broken glass and the battered ruins of discarded domestic machinery, there are the decaying remains of humanity’s meals.

Only a few birds have the behavioural robustness to tolerate such conditions or the digestive systems to cope with the kind of diet to be found here. But for those that have, there is a never-ending supply of food. Just as flamingos form huge flocks on salt lakes because few other kinds of birds can accept such circumstances, so the one or two species of birds that have learned how to make a living on rubbish tips also gather there in spectacular numbers – seagulls in Europe, vultures in South America, kites in India and marabou storks in Africa.

Other species have moved into the city centres to live among the buildings themselves. Pigeons are among the boldest and most numerous. Their ancestors, wild rock pigeons, lived on the cliffs and in the caves of the coast. There they nested alongside kittiwakes and shags, but right from the earliest times, human beings welcomed them into their towns. Pigeons, whether as adults, squabs or eggs, were good for eating and the birds managed to feed themselves by gathering scraps that were far too small for people to eat. Furthermore, the birds could provide fresh meat during the winter when the lack of winter foodstuffs meant that the only domesticated animals that could be left unslaughtered at the end of the summer were breeding stock. The Egyptians and the Romans accordingly provided pigeons with special accommodation, tall towers fitted internally with ledges on which the birds could roost and nest. So the pigeon became one of the first species of bird to be domesticated by humanity.

Strains of them were developed for particular purposes, some specially plump for food, some to race or carry messages by exploiting the pigeons’ ability to return to their nest sites no matter where they were taken, and some simply to delight their owners’ eyes and fancies by becoming oddly coloured or physically deformed. These new strains inevitably escaped and interbred with the wild birds. So eventually, the modern town pigeons appeared, whose variable colours reflect their mixed ancestry. They build their untidy nests on ledges and balconies, in gutters and beneath eaves, just as their ancestors did on the cliffs of the coast. Some have so little fear of human beings that they will sit on the heads, shoulders or hands of anyone who offers them food. A few have even learned how to exploit urban transport systems. In London, it is common enough to see them hop into the carriage of a tube train to prospect for crumbs on the floor inside, and hop out again just as soon as they hear the hiss of air that precedes the closing of the doors. A few brave individuals have even been recorded as staying inside as passengers and travelling to the next station before alighting.

Cities offer other kinds of food as well as refuse. Kestrels hover, head down, searching for mice that might be foraging among the refuse bins. The peregrine falcon that hunted the wild rock pigeons of the coast, has followed its prey. Some use the spires of European cathedrals as lookout posts from which to select their victims, and in New York, they dive down into the canyons between the skyscrapers to pounce on their prey.

In many cities, the bright lights that shine throughout the night attract dense clouds of moths, crickets and other insects. Alpine swifts which have built their nests on buildings in the Swiss city of Geneva have changed their habits to become active after dark for then there are insect swarms which are denser than any they might find during the day.

A male eagle-owl, reared during a breeding programme in Stockholm Zoo and known as Karl-Edvard, became a city dweller by choice. He was released, fitted with a small radio transmitter so that his movements could be checked. Instead of flying off to the countryside, he established himself in the city centre and there met a wild female. The couple paired and on at least one occasion mated on the roof of the Grand Central Station. They built their nest inside the windowless ruin of a coal-fired power station and raised a family there. Karl-Edvard fed his chicks with rats which he caught on a nearby recreation field and regularly paid courteous visits to his caged parents in the zoo, sitting outside their cage and chatting. He also benefited from the city’s veterinary services for once, when he was greatly weakened by pneumonia, he was collected and successfully treated with penicillin. Eventually he moulted the tail feather that carried his transmitter and left it on the roof of the Cavalry headquarters. Thereafter he was able to conduct his affairs in privacy.

Perhaps the most ingenious exploiters of urban conditions are carrion crows that live in a Japanese city. The species is abundant in the mountains and forests of Japan but has also moved into urban areas. In 1990, the birds living in Sendai City somehow discovered that the green globes hanging from walnut trees that line some of the streets contained tasty nuts. But even though their beaks are hefty for crows, they were unable to crack the nuts for themselves. Nor did nuts break when dropped from the air, a technique used by the birds with other shelled morsels. The traffic along the town’s streets provided them with a solution. Some of the birds wait beside the traffic lights at one of the crossroads holding a walnut in their beaks. As soon as the lights turn red, the birds fly down and place the nuts in front of the cars. The lights turn to green, the traffic rolls forward over the nuts, and when it turns red again, the crows hop down into the road and hastily pick up the fragments of the kernels before the traffic starts to move forward once more.

City life may have more subtle attractions for birds than food. In Britain, on autumn evenings, starlings gather in flocks on the outskirts of towns. The hundreds grow into thousands. Then the whole immense assembly takes to the sky for aerial manoeuvres. They swirl in great clouds that swell and taper, coalesce and divide with the birds flying so closely together and with such finely coordinated dives, banks and swoops that it seems that they are all reacting to some common choreographic instructions. The display may last for half an hour or so. As one flock descends on a building and lands on its ledges and parapets, so another arrives to share in the aerobatics until darkness falls, the sky empties and the entire building is laced and dotted with perching birds. It may be that the starlings spend the night in town because it is a degree or so warmer there than in the countryside. The buildings provide a shelter from the wind and, no matter how well insulated they may be internally, inevitably radiate a little heat. It could also be that these immense roosts serve as information centres. Birds that have fed well during the previous day will, the following morning, fly straight back to the same site to resume their meals, and birds that fared less well and have no such motivation will follow them. But why all should perform an aerial ballet is still unexplained.

The fact is that just as country people all over the world seem impelled to migrate to towns, even though when they get there they can find neither homes nor jobs, so some birds also find towns irresistible. Nowhere is this more dramatically apparent and inexplicable that in the central Brazilian town of Manaus. The town stands on the banks of the Amazon and on its outskirts, it has a large oil refinery. Like all such installations, this is filled with deafening unceasing noise. Plumes of flame spurt from pipes as waste gas is burnt off. Rhythmic blasts of steam hiss out in great clouds and condense into drifts of tepid drizzle. Many of the pipes are so hot that they are painful to touch. Others shudder with the violence of the reactions that are going on within them. It is difficult to imagine an environment that is more radically different from the pristine rainforest that still stands a kilometre or so away across the muddy river on the opposite bank. Yet every night, tens of thousands of purple martins leave the forest and fly over to the refinery. For ten minutes or so, blizzards of them swirl down from the darkening sky, dodging aerobatically through the maze of metal, to settle in neat rows along the pipes, rails and ladders. Then the invasion is over and the refinery is festooned with birds. In the hot humid climate of the Amazon, it can hardly be that they have come for warmth. Nor is it likely that there are fewer predators around the refinery than in the forest, for hawks are often circling overhead. Maybe like fish in shoals and antelope in herds, they are seeking the safety that comes from numbers.

Whatever the reason that draws birds to towns, city dwellers all over the world welcome them. Many of the purple martins which roost in the Manaus oil refinery migrate each spring to North America. There they become some of the most pampered of all free-flying birds. Once they found homes for themselves in tree holes. Now human beings provide them with special lodgings. The tradition, it is said, was started by native people, the Choctaw and Chickasaw Indians, who were glad to see the birds when they arrived each spring and hung out hollow gourds to serve as additional nesting places for them. Today, that tradition has been hugely elaborated. Martin-lovers construct special tenements, that may be so big and elaborate that they can accommodate several hundred birds. Some are assemblies of gourds or specially made fibreglass globes. Others are more fanciful and are made in the shape of Siamese temples, railway coaches, or streets from a town in the old wild west. Many are mounted on masts fitted with ropes and pulleys to allow the nest boxes to be lowered so that the human landlord can inspect the inside of the nests to check on the progress of the occupants or the hygiene of the nest linings. They all, however, must have an entrance hole of just the right size – big enough to allow the martin to enter but small enough to prevent starlings from doing the same. Just inside most, there is a baffle to prevent an owl or a raccoon trying to reach inside. As many as half a million people along the eastern United States care for martins in this way, and with such success that today hardly any of the martins in this part of America nest in any other fashion. As a consequence, their numbers are now very much greater than they would be if they still had to find tree holes in which to bring up their families.

This affection for birds on the part of humanity has over the past few centuries led to major changes in the range and distribution of many species. Specimens imported from overseas to be kept caged in collections, public or private, have frequently escaped and found homes for themselves in the wild. In the seventeenth century, King Charles II had his own collection of birds in London’s St James’ Park. Canada geese were among them. By the middle of the eighteenth century, these handsome foreigners were living in English wetlands alongside native mute swans and falling to the guns of wildfowlers. A few may have been migrants from the Arctic that, flying south in autumn, lost their way and crossed the Atlantic by mistake, but most, certainly, were escapees. The conditions in Britain and northern Europe suited them very well. Today, Canada geese are an established element in the British avifauna and flourish in such numbers that, in the eyes of many landowners, they are a major pest, fouling lawns and meadows with their abundant droppings. Those most handsome of ducks, the mandarins, were from the mid-nineteenth century onwards deliberately encouraged to establish themselves in Britain by bird-loving landowners who delighted to see flocks of them on their lakes. It took some time before they found a permanent place for themselves in the wild but now colonies are established in many areas in southern England and are, apparently, safer there than in their native China. The latest, and perhaps most spectacular and surprising exotic species to settle in Britain is the ring-necked parakeet from Asia. It was for long popular as a cage bird, but some eventually escaped. Surprisingly perhaps, these brilliantly coloured birds that seem to belong in a tropical landscape, do not find English winters too bitter. Now there are many large colonies in southern England, and exotic jade-green strangers with red beaks and purple collars are joining blue tits and spotted woodpeckers in collecting peanuts from feeders in suburban gardens.

During the nineteenth century, Europeans who had emigrated and settled on other continents also began to import birds. They were not content with the unfamiliar and often glamorously coloured birds that they found in their new surroundings but yearned for European species. In the 1850s, European house sparrows were released in Brooklyn and a hundred other cities in the United States and Canada on the improbable grounds that they might help keep local insects under control – in spite of the fact that, as anyone could see, sparrows are primarily seed-eaters. By the end of the century they were nesting in every state in the Union. European starlings were liberated in New York’s Central Park. Within fifty years they had spread right across the continent and had reached California in the west, Alaska in the north and the Mexican border in the south.

European colonists in Australia and New Zealand were particularly enthusiastic about importing animals and plants of all kinds to supplement what they regarded as the commercially unsatisfactory and aesthetically unpleasing native fauna and flora. Every state in Australia formed its own Acclimatisation Society which set about putting things right. Prickly pear, a spiny succulent from South America which spread and destroyed great areas of potentially productive pasture, was originally imported by the infant colony of New South Wales to provide food for the cochineal insect – which itself was imported to provide red dye for the uniforms of the military. Rabbits were introduced for their flesh and their fur, and when their numbers in the wild began to increase astronomically, mongooses from India were released to keep down the rabbits – upon which they had little effect. Cats were brought by settlers who liked to have them as household pets, and foxes by those who found their pleasure in putting on red coats and galloping off to chase them through the groves of eucalyptus.

Naturally enough, bird-loving members of these societies also set about improving the Australian avifauna. Secretarybirds from Africa were introduced in hope that they might reduce the numbers of native snakes – but apparently had little success and did not survive long. Starlings and sparrows were introduced in bulk, as they had been in the United States, to control insect pests. They flourished mightily but ate few insects. Other British birds were released so that, in the words of one society’s prospectus, ‘they may be permanently established here and impart to our somewhat unmelodious hills and woods, the music and harmony of English country life’. So hundreds of song thrushes, blackbirds, linnets, robins, redpolls, skylarks, goldfinches, greenfinches, bullfinches, chaffinches and yellowhammers were released into the Australian bush. Some species failed to establish themselves but others increased so greatly in numbers that in some areas they became the most abundant of all the local birds.

The indigenous birds, of course, were badly oppressed by those foreign invaders that settled successfully. Before this time, the only mammalian carnivores they had had to face were the relatively clumsy Tasmanian devils which were, in any case, primarily carrion feeders, and the small quolls which the English settlers called first, ‘native polecats’ and then more simply, ‘native cats’. But the pet European cats that escaped into the wild were much more efficient bird hunters. Stoats and weasels that had been imported to control the rabbits also found local birds a much easier prey. Rats that no one had planned to introduce but which had nonetheless travelled in the holds of ships and clambered ashore along the mooring ropes, pillaged their eggs and slaughtered their chicks. And European birds took their food and occupied their nesting sites.

The damage was at its worst in New Zealand. The original absence of any land mammals whatever had allowed the native birds to lower their defences to such a degree that they took little trouble to nest in safe places and many had lost their power of flight. The carnage began some twelve hundred years ago when the first human beings arrived. They were Polynesians who had come in canoes from warmer islands away to the north. They found the flightless moas, some species grazing the meadows, others living in the forests and browsing among the trees. All were good to eat and the Polynesians hunted them with great efficiency. As the human population of the islands grew, the native forests were reduced, and the hunting of the giant birds became more intensive. They were snared and trapped, driven into swamps and clubbed to death. By three hundred years ago all of the moas were extinct. The arrival of the Europeans and the alien mammals and birds they brought with them greatly accelerated the devastation of the native fauna. Now it was not just those birds that were hunted for food that suffered. Now it was anything that could be caught by a cat, a rat or a stoat. The European settlers hastened the process of clearing the native forests in order to make space for their sheep and cattle. Few of the local birds could withstand these new pressures. At least 50 per cent of New Zealand’s species of native birds became extinct, eighteen of them within the last century and a half.

Flightless birds on other islands elsewhere in the world were equally vulnerable. The first animal exterminated by European man in historic times was one of them and was massacred so swiftly that its very name has become synonymous with extinction – the dodo. It lived on the island of Mauritius in the Indian Ocean. It was probably a member of the pigeon family that, like so many island birds, had become a flightless giant. Its island sanctuary was so remote that human beings did not discover it until the beginning of the sixteenth century. It was not until the seventeenth century that ships called at Mauritius with any frequency but then the sailors who landed there were only too glad to get fresh meat and had no difficulty in clubbing the huge defenceless dodos. The last of them was slaughtered in 1681, less than two hundred years after men had first landed on the island.

A giant flightless seabird, the great auk, which stood 75 centimetres high, once lived in the northern Atlantic. In the sea it was a powerful swimmer able to out-pace a rowing boat, but when it came ashore to lay its eggs, then it too was easily caught. And it too was edible. As men’s mastery of these tempestuous northern seas became greater so they found every one of the islands on which the great auks nested and the huge birds became increasingly scarce. The last British great auk was caught on St Kilda, a lonely islet lying in the Atlantic west of the Outer Hebrides, and beaten to death in the belief that it was a witch. The last of all was killed in Iceland in 1844.

The invention of efficient and accurate hand guns brought even fully flighted birds within easy range of human hunters. The most numerous bird ever to have existed is thought to have been the passenger pigeon. Only two hundred years ago, the skies above the grasslands in the central United States were regularly darkened by immense flocks of them. One was estimated to contain two thousand million individuals and took three days to fly past. A century ago, people began to notice that passenger pigeons were not as abundant as they had been. The full cause of their decline is now uncertain. Deforestation as the land was brought into cultivation is now thought to be one of the causes of their decline, but intensive hunting was also undoubtedly a factor. No one worried very much about their shrinking numbers until the species was on the brink of extinction. By then it was too late. The last wild passenger pigeon was sighted in 1889 and the last surviving individual, a lonely captive female named Martha, died in Cincinnati Zoo in 1914.

By the middle of the twentieth century, human beings were at last becoming aware of the damage that they were inflicting upon the world’s wildlife and the movement to conserve began to gather momentum. There was no shortage of bird species in urgent need of help. The ne-ne, a goose that evolved on the lava fields of Hawaii, had been reduced to about thirty-five wild individuals and fifteen captives. A group of dedicated ornithologists, among them Sir Peter Scott, started a programme of intensive captive breeding. This was so successful that by 1960 it was possible to take groups back to Hawaii and release them in the wild.

In New Zealand, ornithologists anxiously surveyed the wreckage of their native avifauna and started to compile censuses of the survivors. In 1970, a scientist visited the Chatham Islands, a small archipelago 885 kilometres east of the main islands. This was known to be the only home of a unique species of New Zealand robin. The species on the mainland is dark grey and white. The Chatham Island species is entirely black. The scientist found that because of introduced predators and changes in the islands’ vegetation, the black robins now survived only on a small rocky islet surrounded by steep cliffs called Little Mangere. There were only eighteen individuals and even they were hard pressed. The forest on which they relied for food had been almost destroyed to create a landing-pad for helicopters serving ships fishing for crayfish. Even the remaining patches had been badly damaged by huge numbers of mutton birds which were digging so many burrows that the trees were tumbling over. As the forest continued to degrade, so there was less and less living space for the robins. By 1976 only seven of them were left and of these, only two were females. They were almost certainly the rarest birds in the world.

The New Zealand Wildlife Service decided that desperate measures had to be taken if the species was not to vanish altogether. A large patch of native forest was still flourishing on the neighbouring rather bigger island of Mangere. A team led by Don Merton tackled the job of trapping the surviving robins, transporting them across the hundred-metre-wide strait to the bigger island and then taking them to the forest on its far side. The operation, which was almost as hazardous for the trappers as it was for the trapped, was managed, amazingly, without the loss of a single bird. One of the females bred that year and in the following seasons other chicks were raised. But by now several of the birds of the original transfer had died of old age. By 1978, only five black robins were left and there were still only two females. Some way had to be found to maximise the eggs produced by these two females before some sudden and unpredictable disaster overcame them or they too died of old age. Time was not on the team’s side. It was known that, if a female black robin lost her first clutch, she would lay a second time. So in 1981, eggs were taken one by one from a nest and put in the nests of Chatham Island warblers, a much more abundant species. The technique worked. The female laid a second time. There were failures and problems in rearing the chicks, but by 1985 the population had grown to thirty-eight. Today there are around two hundred and fifty and the species, though still extremely rare on a world scale, seems to be out of immediate danger in the islands on which it evolved. When they analysed the history of the rescue, researchers realised that all today’s population are the descendants of just one of those two original females. She was known from the colour of the identifying band on her leg as Old Blue. She had lived for thirteen years, twice as long as expected for her species. The black robin’s escape from extinction could not have been narrower.

Encouraged by this success, Merton and his group went on to try to help one of the most dramatic and astonishing of New Zealand’s birds, the giant nocturnal flightless parrot, the kakapo. In 1960, it was believed by most authorities that the species had been lost, but in that year, signs of them were found in Fiordland, the most remote tract of New Zealand’s wilderness in the southwest corner of South Island. Five of them were trapped and taken into a reserve for study, but they all proved to be males. Keeping track of the fortunes of the birds in the wild was extraordinarily difficult because the only practical way to reach the ridges and valleys where they lived was by helicopter. In 1974, a male and a smaller individual that was thought to be a female were trapped and sent to an island sanctuary to see if they could be persuaded to breed. But they showed no sign of doing so and when eventually they both died the putative female was found to have been a male. More expeditions discovered eighteen birds in the wild, but they were widely scattered and seemed out of contact with one another. And all were judged to be elderly males. Hopes for the survival of the kakapo seemed very faint indeed.

Then in 1977 a new population of about two hundred was found on Stewart Island, a fragment of land, 80 kilometres across, lying off the southernmost point of South Island. This seemed to be a more viable and vigorous population and contained some undoubted females. Hope was renewed. But in 1982, cats somehow reached the valleys where the birds lived. Remains were found of no less than sixteen kakapo which they had killed. Attempts were made to exterminate the cats around the kakapos’ refuge but everyone realised that they could never be entirely eliminated from such a big island with an established human population. The Stewart Island kakapo also seemed to be heading for extinction.

Once again, radical measures were called for. Merton and his team were given permission to catch the entire Stewart Island population and move them to four small islands that had been totally cleared of alien predators. Sixty-one birds were caught, but to everyone’s dismay, once again the majority were males. The birds settled down well in their new homes, but by now it had been discovered that the conditions kakapo require to breed are particularly demanding.

The males are polygamous. Each has his own territory within which he creates a number of shallow saucer-shaped depressions in which during the night he crouches, puffs himself up and makes booming calls. The females, attracted by the sound, select one male, mate with him beside his auditorium and then go away to lay their eggs and rear their chicks with no further help from him. But the birds have to build up huge bodily reserves that almost double their weight in order to be able to do this – the males so that they can devote much of their time during the nights visiting their booming-bowls and calling, the females in order to produce their eggs and feed the chicks, without help, for many months. Even in the most favourable environments, they cannot do so every season. In their original homes, the birds probably relied on the fruit of the podocarp trees that had dominated the lowland forests to bring them into breeding condition. In Fiordland and Stewart Island much of these forests had been felled and alien predators had driven the survivors from the small patches that remained. The birds in Fiordland had been found living high in the mountains where there was probably not enough good food to bring them into breeding condition anyway. This explained the fact that there were no young birds in the population. If this was the case, then the survivors in their new predator-free homes might manage to live for the length of their natural life, but they would never breed either, for the vegetation in their new environment was also likely to be inadequate. In a technical sense, therefore, the kakapo was probably extinct already.

The only solution was to provide supplementary food. That was started in 1993. By now only nineteen females were left. In 1995, fifteen nests were discovered but of the thirty-two eggs that were laid in them only thirteen were fertile and hatched. In 1997, however, the booms of the males were heard more frequently than ever before, and by January 1998 seven young kakapo had hatched successfully. By 2005, there were kakapo populations on four islands, numbering eighty-six individuals, and numbers increased slowly over the following years, reaching two hundred and fifty-two individuals in 2022. So now there is a real chance that this remarkable bird may yet survive.

In the United States, species of birds continued to become endangered even after the extermination of the passenger pigeon as more and more wild country was claimed by human beings for their own purposes. The biggest of North American birds, the noble whooping crane, which stands 1.5 metres tall, was once a relatively common sight. But the draining of swamps on which it relied for food reduced its numbers year after year. By 1945, only sixteen individuals remained. Once again, at the very last moment, conservationists mounted a last-ditch rescue. Reserves were created for them. Hunters, who regarded any wildfowl of any kind as fair game, were warned of the impending catastrophe and told how to distinguish the whooping crane from smaller commoner relatives such as the sandhill crane, in the hope that they would spare them. Even so, the number of whoopers remained dangerously low. At this stage, George Archibald came to their rescue. He established a captive flock at his research centre in Wisconsin. Here he pioneered the technique that was later to be used by Don Merton in New Zealand, of taking the first clutch from the birds and putting them in the nests of adults of a different kind. Sandhill cranes, a much more common species, proved to be admirable foster parents.

Archibald raised eighty-four chicks using this technique. But then a new problem appeared. The chicks had become imprinted on their foster parents and clearly regarded themselves as sandhill cranes. Thus when they reached breeding age they would not respond to whooper courtship displays and would only accept a sandhill crane as a partner. A new technique had to be devised. Today, Archibald and his team place the eggs in incubators. A chick, when it hatches, finds itself in an indoor enclosure. A head, with the black streaks on either side of the beak and a black patch on the back of the head which are the diagnostic signs of a whooping crane, suddenly appears through a trap-door in one wall. It cranes down on its long neck, picks up a particle of food in its beak and offers it to the youngster. It is a sleeve puppet on the arm of one of the rearing team. For the next two weeks, while the chick is at its most impressionable, this is the only moving object it sees. Its human foster parent remains out of sight guiding the actions of the puppet by watching the operation through a one-way mirror. Even when the chick ventures out into a paddock, it is placed under the care, not of a sandhill crane but of a human helper wearing a whooping crane costume.

But one final problem remains. Whooping cranes migrate. They fly south to spend the winter in New Mexico and the Gulf coast of Texas, travelling in family parties, guided by the parent birds. If the hand-reared youngsters were released into the wild, as all concerned with whooping crane protection hope they will be, then they could well respond to an in-built migrationary urge and set off south. But how would they find their way and – even more difficult – how could they discover the few reserves in the south where whooping cranes can be sure of spending the winter in safety?

That problem was tackled by an Idaho farmer, Kent Clegg, whose passion was not only for birds but also for aeroplanes. Clegg reared whooping cranes but used a different technique from that used by George Archibald. A group of them were hatched out together, Kent believing that if they were kept as a flock, there would be no problems about imprinting later in life. He also trained them from an early age to come to his calls and to follow him. As they approached adult size, he took them out for daily walks, leading them from a motorised farm buggy. Then he introduced them to his microlite aircraft. As he took off, so he would call to them and they would follow, flying in formation in a line stretching outward from the aircraft’s wing, as they would do if their leader were an adult bird.

The refuge in New Mexico is some 1,200 kilometres away to the south. The two previous years, Kent had led groups of imprinted sandhill cranes down there, so he knew the route and the problems, and that the project was feasible. Another experienced microlite pilot would join him in the air, to try to fend off any attacks by eagles. A support party would travel by road with collapsible pens in which the birds could be kept out of danger during the night.

The flock was small – eight sandhill cranes and just four precious whoopers. All twelve carried small radio transmitters so that they could be traced if, somehow, they got lost. Kent took off in his microlite and the flock followed him into the air, but as he headed south they wheeled round north and settled back on one of their familiar home fields. Kent tried again but without success. The young birds’ tie with their home territory was too strong. So he loaded them on to a trailer and took them to another location, 25 kilometres away, where they could not see the fields where they had grown up. This time all went well and Kent, with the twelve birds flying in a line from his wing tip, headed south.

At midday, the birds landed for rest and refreshments. In the evening Kent led them off again and that day they covered over a hundred kilometres. On the third day, disaster struck. A golden eagle attacked. The bird was driven off by the escort plane, which fired special blank shells at it, but not before one of the whoopers had been struck out of the sky. Fortunately, the eagle had not been able to inflict the heavy body wound that is normally fatal, but had only gashed the whooper’s thigh. The ground party managed to catch the bird and get veterinary help. The wound was sewn up, the patient was given a dose of antibiotics, and was transported for the next few days by road in a trailer. On the seventh day out, the whole party was almost totally scattered, no doubt quite unknowingly, by a squadron of jet fighters which roared over them at low altitude. The cranes, as always when frightened in the air, clustered round Kent’s microlite – coming so close that they nearly collided with him. But on the ninth day, he led them down to the Bosque Del Apache Reserve near the Rio Grande. For two days, Kent stayed with them, leading the birds down to the swamp to mingle with the resident population of sandhill cranes. Then he left them.

Watching Kent Clegg patiently instructing his charges in how to find their way through the skies was both a touching and a paradoxical sight. Birds, after all, have been flying from continent to continent for at least a hundred million years and we have only just started to do so. But that is only one particularly vivid demonstration of how recently we have acquired our dominance. They, long ago, took up residence in the Antarctic, the coldest place on earth on which we only set foot less than two centuries ago. They live and breed in deserts where no human being has ever survived unaided for any length of time. They can stay in the air for a year or more and girdle the earth, which we have only learned to do within the last few decades.

We are now the most widespread competitors that birds have ever had to face. We are also by far the most powerful. We have already exterminated whole species of them by direct attack, but the greatest destruction we have wrought has been inadvertent – a consequence of the wholesale changes we have made to the face of the earth. That damage need not continue. We now have the knowledge and the skill to maintain all the wonderfully rich range of birds that still exists on earth in all its complexity and glory. All we need, as the new masters of this planet, is the will to do so.