494 



NATURE 



[September 21, 1893 



Africa. (4a) Down the Volga by the Sea of Azof, Asia Minor, 

 and Egypt, while the other portion (4*), trending east, passes 

 by the Caspian and Tigris to the Persian Gulf. (5) By the 

 Yenesei to Lake Baikal and Mongolia. (6) By the Lena on to 

 the Amoor and Japan. (7) From East Siberia to the Corea 

 and Japan. (8) Kamschatka to Japan and the Chinese coast. 

 (9) From Greenland, Iceland, and the Farohs, to Britain, where 

 it joins line 2. 



All courses of rivers of importance form minor routes, and 

 consideration of these lines of migration might serve to explain 

 the fact of North American stragglers, the waifs and strays 

 which have fallen in with great flights of the regular migrants 

 and been more frequently shot on the east coast of England and 

 Scotland than on the west coast or in Ireland. They have not 

 crossed the Atlantic, but have come from the far north, where a 

 very slight deflection east or west might alter their whole course, 

 and in that case they would naturally strike either Iceland or 

 the west coast of Norway, and in either case would reach the 

 east coast of Britain. But, if by storms, and the prevailing 

 winds of the North Atlantic coming from the west, they had 

 been driven out of their usual course, they would strike the 

 coast of Norway, and so find their way hither in the company 

 of their congeners. 



As to the elevation at which migratory flights are carried on, 

 Herr Ga'ke, as well as many American observers, holds that it 

 is generally far above our ken, at least in normal conditions of 

 the atmosphere, and that the opportunities of observation, 

 apart from seasons and unusual atmospheric disturbance, are 

 confined chiefly to unsuccessful and abortive attempts. It is 

 maintained that the height of flight is some 150010 15,000 feet, 

 and if this be so, as there seems every reason to admit, the aid 

 of land bridges and river valleys becomes of very slight im- 

 portance. A trivial instance will illustrate this. There are two 

 species of blue-throat, Cyanecula suecica SluA C. leucocyana: [ht 

 former with its red-breast patch is abundant in Sweden in 

 summer, but is never found in Germany, except most accident- 

 ally, as the other is the common form of Central Europe. Yet 

 both are abundant in Egypt and Syria, where they winter, and 

 I have on several occasions obtained both species out of the 

 same flock. Hence we infer that the Swedish bird makes its 

 journey from its winter quarters with scarcely a halt, while the 

 other proceeds leisurely to its nearer summer quarters. On the 

 other hand, I have more than once seen myriads of swallows, 

 martins, sand-martins, and, later in the season, swifts, pasNing 

 up the Jordan Valley and along the Bukoa of Central Syria, at 

 so slight an elevation that I wa^ able to distinguish at once that 

 the flight consisted of swallows or house-martins. This was in 

 perfectly calm clear weather. One stream of swallows, certainly 

 not less than a quarter of a mile wide, occupied more than half an 

 hour in passing over one spot, and flights of house-martins, and 

 then of sand-martins, the next day, were scarcely less numerous. 

 These flights must have been straight up from the Red Sea, and 

 may have been the general assembly of all those which had win- 

 tered in East Africa. I cannot think that these flights were 

 more than 1000 feet high. On the other hand, when standing 

 on the highest peak in the Island of Palma, 6500 feet, with a 

 dense mass of clouds beneath us, leaving nothing of land or sea 

 visible, save the distant Peak of Tenerife, 13,000 feet, I have 

 watched a flock of Cornish choughs soaring above us, till at 

 length they were absolutely undistinguishable by us except with 

 field-glasses. 



As to the speed with which the migration flights are accom- 

 plished, they require much further observation. Herr Giitke main- 

 tains that godwits and plovers can fly at the rate of 240 miles an 

 hour(!), and the late Ur. Jerdon slated that the spine-tailed 

 swift (Acaiithyllis catidacictus), roosting in Ceylon, would reach 

 the Himalayas (1200 miles) before sunset. Certainly in their 

 ordinary flight the swift is the only bird I have ever noticed to 

 outstrip an express train on the Great Northern Railway. 



Observation has shown us that, while there is a regular and 

 uniform migration in the case of some species, yet that, beyond 

 these, there comes a partial migration of some species, immi- 

 grants and emigrants simultaneously, and this, besides the 

 familiar vertical emigration from higher to lower altitudesand vice 

 versd, as in the familiar instance ofthe lapwing and golden olover. 

 There is still much scope for the field naturalist in observation 

 of these pirtial migrations. There are also species in which 

 some individuals mi^jrate and som2 are sedentary, ?.^. in the 

 few primeval forests which still remxin in the Canary Islands, 

 ani which are en;hrouded in alm:)St perpetual mist, the wo )d- 



NO. T247, "^'^'^L. 48] 



cock is sedentary, and not uncommon. I have often put up the 

 bird and seen the eggs ; but in winter the number is vastly in- 

 creased, and the visitors are easily to be distinguished from the 

 residents by their lighter colour and larger size. The resident 

 never leaves the cover of the dense forest, where the growth of 

 ferns and shru;>s is perpetual, and fosters a moist, rich, semi- 

 peaty soil, in which the woodcock finds abundant food all the 

 year, and has thus lost its migratory instincts. 



But why do birds migrate ? Observation has brought to light 

 many facts which seem to increase the difficulties of asatislac- 

 tory answer to the question. The autumnal retreat from the 

 breeding quarters might be explained by a want of sufficient 

 sustenance as winter approaches in the higher latitudes, but this 

 will not account for the return migration in spring, since there 

 is no perceptible diminution of supplies in the winter quarters. 

 A friend of mine, who was for some time stationed at an infir- 

 mary at Kikombo, on the high plateau south-east of Victoria 

 Nyanza Lake, almost under the equator, where there is no 

 variation in the seasons, wrote to me that from November to 

 March the country swarmed with swallows and martins, which 

 seemed to the casual observer to consist almost wholly of our 

 three species, though occasionally a few birds of different type 

 might be noticed in the larger flocks. Towards the end of 

 March, without any observable change in climatic or atmospheric 

 conditions, nine-tenths of the birds suddenly disappeared, and 

 only a sprinkling remained. These, which had previousl}' been 

 lost amid the myriad of winter visitants, seemed to consist of 

 four species, of which I received specimens of two, Hirundo 

 puella and H. senegaknsis. One, described as white underneath, 

 is probably H. athiopica ; and the fourth, very small, and quite 

 black, must be a Psalidoprocne. All these remained through 

 spring and summer. The northward movement of all the others 

 muht be through some impulse not yet ascertained. In many 

 other insiances observation has shown that the impulse of move- 

 ment is not dependent on the weather at the moment. This is 

 especially the case with sea birds. Prof Newton observes 

 that they can be trusted as the almanack itself. Foul weather 

 or fair, heat or cold, the puffins, Fratcrcula arctica, repair to 

 some of their stations punctually on a given day, as if their 

 movements were regulated by clockwork. In like manner, 

 whether the summer be cold or hot, the swifts leave their su niuer 

 home in England about the first week in August, only occasional 

 straggleis ever being seen after that date. So in three difierent 

 years I noticed the appearance of the common swift (Cypselus 

 aptis) in myriads on one day in the first week in April. In the 

 case of almost all the land birds, it has been ascerlain.;d by 

 repeated observations that the male bi'-ds arrive some days before 

 the hens. I do not think it is proved that they start earlier ; 

 but, being generally stronger than the females, it is very natural 

 that they should outstrip their weaker mates. I think, too, that 

 there is evidence that those species which have the mo t extended 

 southerly, have also the most extended northerly range. The 

 same may hold good of individuals of the same species, and may 

 be accounted for by, or account for, the fact that, e.g., the indi- 

 viduals of the whealear or of the willow wren which penetrate 

 furthest north have longer and stronger wings than those indi- 

 viduals which terminate their journey in more southern latit ides. 

 The length of wing of two specimens of Saxkola <znanthe in 

 my collection from Greenland and Labrador exceeds by '6 inch 

 the length of British and Syrian specimens, and the next longest, 

 exceeding them by '5 inch, is from the Gambia. So the seden- 

 tary Phylloscopus trochilns of the Canaries has a perceptibly 

 shorter wing than European specimens. 



To say that migration is performed by instinct is no explana- 

 tion of the marvellous faculty, it is an evasion of the difficuliy. 

 Prof. MoSius holds that birds crossing the ocean may be guided 

 by observing the rolling ofthe waves, but this will not hold good 

 in the varying storms of the Atlantic, still less in the vast stretch 

 of stormy and landless ocean crossed by the bronze cuckoo 

 {Chrysococcyx lucidus) in its passage from New Guinea to New 

 Zealand. Prof. Palmcn ascribes the due performance of the 

 flight to experience, but this is not confirmed by field observers. 

 He assumes that the flights are led by the oldest and strongest, 

 but observation by Herr Giitke has shown that among migrants, 

 as the young and old journey apart and by different routes, the 

 former can have had no experience. All ornithologists are aware 

 that the parent cuckoos leave this country lont> before their young 

 ones are hatched by their foster-parents. The sense of si^ht 

 cannot guide birds which travel by night, or span oceans or con- 

 inents in a single flight. In noticing all the phenomena of 



