792 BEPOET — 1893. 



autuuiDal 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 as a missionary 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 

 previously been lost amid the myriad of winter visitants, seemed to consist of four 

 species, of which T received specimens of two, Hirundo puella and H. senegalensis. 

 One, described as white underneath, is probably !/■. cethiojnca; and the fourth, very 

 small, and qiiite black, must be a PsalichjJrocne. All these remained through 

 spring and summer. The northward movement of all the others must be 

 through some impulse not yet ascertained. In many other instances observa- 

 tion has shown that the impulse of movement is not dependent on the weather 

 at the moment. This is especially the case with sea birds. Professor Newton 

 observes thev can b3 trusted as the almanack itself. Foul weather or fair, heat 

 or cold, the f)utfins, Fratercula 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 summer 

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

 ever being seen after that date. So in three different years in Syria I noticed the 

 appearance of the common swift {Cypselus ajim) in myriads on one day in the 

 first week in April. In the case of almost all the land birds, it has been ascer- 

 tained by repeated observations that the male birds arrive some days before the 

 hens. 1 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 most extended southerly have also the most e.xtended northerlj^ 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 individuals of the wheatear or of 

 the willow wren which penetrate furthest north have longer and stronger wings 

 than those individuals which terminate their journey in more southern latitudes. 

 The length of wing of two specimens of Sa.ricola ananthe 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 sedentary Phjlloscopus trochilus of the Canaries has a perceptibly shorter 

 wing than European specimens. 



To say that migration is performed by instinct is no explanation of the mar- 

 vellous faculty, it is an evasion of the difficulty. Professor Mobius holds that 

 birds crossing the ocean may be guided by observing the rolling of the 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. Professor Palra^n 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 long before 

 their young ones are hatched by their foster-parents. The sense of sight cannot 

 guide birds which travel by night, or span oceans or continents in a single flight. 

 In noticing all the phenomena of migration, there yet remains a vast untilled 

 region for the field naturalist. 



What Professor Newton terms ' the sense of direction, unconsciously exercised,' 

 is the nearest approach jet made to a solution of the problem. He remarks 



