Who would dare travel from Germany to South Africa and back without map or signposts, without ever asking anyone the way, without a travelling com­panion who knows the route, or anyone showing or telling him beforehand how to reach his destination? This is equivalent to what millions of birds of passage do every year, including finding on return their precise place of birth-say back garden, second oak on left, of house No. X, Y Street, in Z district of a particular town. When we think of the achievement involved, it makes us gasp. But in other parts of the world the phenomenon of bird migration assumes even more amazing forms than in the air passage between Europe and Africa.

While the European cuckoo migrates to Central Africa, its New Zealand relative, the bronze cuckoo (Ghalcites Cuccolus) leaves a time-table for its young as well. Dr. E. Thomas Gilliard' reports that as soon as the female has laid her eggs in the nests of other small birds, she takes up her winter quarters. Her young, lovingly brought up by strange mothers, follow her there a month later on their own and without her guidance.

First their route runs west for1,250 miles to Australia across an enormous expanse of ocean without islands. After pausing briefly for rest and food in Australia, they continue their journey due north along die whole coastline, and pass over New Guinea to the Bismarck Archipelago. Here at last, after covering a flight distance totalling nearly 4,000 miles, they join their parents whom they have never seen before and of course do not recognize as members of their family. Yet it was these parents who gave them their ”flight tickets” even before they were hatched.

Then there is the slender~billed shearwater (Puffinus tenuirostris), which every year flies halfway around the Pacific Ocean. In 1798, when for the first time Captain Flinders and his ship's surgeon, Dr. Bass, crossed the straits between Australia and Tasmania now called the Bass Straits, they reported: “The birds passed over us continuously for 90 minutes in a dense flock about 300 yards wide. We estimated their number at 151 millions.”

Today's estimates would give about the same numbers, although for some decades many have been shot for canned meat (they taste rather like mutton). At any rate, the flock of shearwaters is enormous. Where does it-hail from and where is it bound for? To find this out, two zoologists, John Warham and Dr. D. L. Serventy, ringed 32,000 birds in die early 1960s. They traced the birds' route and established the following round-the-world timetable:
Arrival on the island breeding-grounds between Australia and Tasmania occurs during the nights of September 26 and 27. After some days of courting and mating all die birds disappear again into the expanses of the ocean. But on November 19 the flock, numbering millions, is suddenly back again to lay their eggs in earth furrows. First the male incubates them for a fortnight, while the female fishes the high sea more than a thousand miles away. Then the partners take turns of between eleven and fourteen days on the nest. By the middle of January the young are hatched and are then fed till the middle of April.
Then the great flight starts. The flock of millions first travel 6,000 miles north across the Coral Sea, and by way of Melanesia and Micronesia through the Straits of Korea into the Sea of Japan.

In June the flock shows up in the Bering Sea between Siberia and Alaska, to move southwards along the Pacific coast of Canada in August. At about the latitude of the frontier between Canada and die United States, the shear-waters veer to a south-westerly course and cross the entire central Pacific ocean by way of Hawaii and the Fiji Islands, to arrive again after a total Right distance of over twenty thousand miles on the shores of Tasmania punctually to the very day, on September 26 and 27.
So far it has been assumed that animals and particularly migrant birds used the day-length as an indication for their ,internal calendar.' With the shear­waters, however, which within a few days pass through latitudes with very different day-lengths, it does not seem as if this time gauge would work. At present, therefore, it is still a mystery what calendar the bird does use so that it can migrate with such precision.


AlbatrosThe bird's western relative, the greater shearwater (Puffinus gravis), covers a mere 15,000 miles a year. But it too achieves a miracle of navigation, starting from Scandinavia, Greenland, Iceland, and Newfoundland, flying almost exclusively over the sea, and finding its way to the remote and tiny archipelago of Tristan da Cunha, in the middle of the South Atlantic, where
it nests with four million of its species. It seems to be absolutely sure of its route, for it starts its courtship while still on the high seas.
Eternal summer and perpetual sunshine are the dream of the Arctic tern (Sterna paradisaea), a restless wanderer from Pole to Pole, from the Arctic to the Antarctic and back again. Almost as soon as the midnight sun has sunk below die horizon on the shores of West Greenland and die islands of North Canada, the birds start out again for the southern tip of Greenland, then continue their Right to die western European seaboard, where they join Rocks of Icelandic members of their species.

Together they fly on to the African coast. At the latitude of Dakar the Rocks part. Some of them fly on to Cape Town, then cross to the Antarctic Continent, where by now summer has started. The rest of the birds fly across the Atlantic, following the normal air-line route from Europe to die coast of Brazil. From there they turn south by way of Tierra del Fuego or the Falkland Islands to the Antarctic peninsula, where they join other members of their species, which have started out from Alaska and flown along die whole Pacific coast of North and South America.

It is perhaps not so surprising that sea-birds should be capable of crossing oceans; what seems quite fantastic is the carrying out of long overseas Rights by birds that cannot swim. I have already mentioned the 1,25~mile Right of the bronze cuckoo, but that is far surpassed by the American golden plover (Pluvialis dominica), a bird related to the lapwing (Vanellus vanellus), and a little smaller than a pigeon. These birds start out from Alaska on a 2,5~mile non-stop Right to Hawaii. Part of them spend die winter there, but others fly just as far again to the Marquesas Islands in the Pacific.

the Mongolian plover flies annually from Siberia by way of Malaya and die Indonesian Islands to Australia, or over India and then nearly three thousand miles across the Indian Ocean to South Africa. This route, incidentally, is also taken by the lesser cuckoo which breeds in China.

AlbatrosKing among die world-tour birds is the albatross, that white oceanic bird with a wing span of between nine and thirteen feet. Albatrosses have been recorded as flying up to fifty miles an hour, without once Rapping their wings. This bird is master of a technique which we humans have so far not been able to copy: dynamic gliding. It glides continuously, dose to the surface of die sea, using variations in die strength of die wind to provide lift. By wing this ,dynamic gliding,' albatrosses largely avoid die necessity for powered Right.

The albatross flies so far and over such isolated regions of the sea that so far no one has been able to trace its route. But an experiment carried out by scientists for the United States Navy had an astonishing result. On one of the Midway Islands a breeding colony of Laysan albatrosses (Diomeaea im­mutabilis) interfered with the Rights of a new air base. So die zoologists wanted to transfer the birds to a place from where they were sure not to return to Midway.

As a test, eighteen grown albatrosses were taken by plane a distance of over three thousand miles in various directions to the state of Washington, Alaska, Japan, New Guinea, and Samoa. The experiment was a total failure. From all these Pacific coasts fourteen albatrosses returned within a short time to Midway, the fastest of them after only ten days: a homing feat that would turn breeders of pize~winning homing pigeons green with envy.

The albatross, however, does not hold the speed record. The same speed is attained by the barn swallow (Hirundo rustica), which spends the winter in southern Africa; while the European swift (Cypoelus apus) is even faster, Rying at about a mile a minute. At present the fastest bird in die world is thought to be its East Asian relative, die spine-tailed swift (Chaetura cau­dacuta), which flies from eastern Siberia via Japan, the Pacific Ocean, New Guinea, and Australia to Tasmania. With this bird a top speed of ninety miles an hour has been recorded-although die maximum speed attainable by an individual bird has no relation to its mean speed of migration.

We still know very little about the height at which migratory birds fly. Professor Ernst Schüz has compiled some interesting observations. If the weather is fine, they often fly so high that they cannot even be seen withthe naked eye. Several ,large birds' (their identity could not be discovered) have been sighted from planes at heights of between 6,000 and 12,000 feet over the North Sea and the English Channel.

After making observations with a small anti-aircraft range finder on die bird island of Mellum, east of the German North Sea spa of Wangerooge, Dr. H. Rittinghaus  reported that in that locality he had seen no larks or golden plovers flying higher than 1,200 feet. According to Rittinghaus, lapwings and hooded crows observed there hardly ever rose above 1,500 feet, while jackdaws reached 2,100 feet at most, and rooks 2,250.

Generally this seems to be the most favourable height. From 2,100 feet the birds can dieoretically see 75 miles. Also, tuis is not yet too cold, and die air still contains plenty of oxygen.

But Siberian storks and ruffs have to surmount die snow-capped giants of die Himalayas. It has been reliably observed that in doing this they must climb to a height of 18,000 feet so as to fly through a pass towards warm India.


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