476 FIELD STUDY IN ORNITHOLOGY. 



l)ir(l I have ever noticed to outstrip an express train on the Great 

 Northern llailway. 



Observation has shown us that, wliile there is a reguLir and uniform 

 miiiration in the case of some species, yet that, beyond tliese, there 

 comes a i)artial migration of some species, immigrants and emigrants 

 simultaneously, and this, besides the familiar vertical emigration from 

 higher to lower altitudes and rice rersa, as in the familiar instance of 

 the lapwing and golden plover. There is still much scope for the field 

 naturalist in observation of these partial migrations. There are also 

 species in which some individuals migrate and some are sedentary, e. </., 

 in the few primeval forests which still remain in the Caiiaiy Islands, 

 and which are enshrouded in almost perpetual mist, the woodcock is 

 sedentary and not uncommon. 1 have often put up the bird and seen 

 the eggs; but in winter the number is vastly increased, and the visitors 

 are easily to be distinguished from the residents by their lighter color 

 and larger size. The resident never leaves the cover of the dense for- 

 est, where the growth of ferns and shrubs is perpetual and fosters a 

 moist, rich, semipeaty 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 a satisfactory 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 migra- 

 tion in the spring, since there is no perceptible diminution of supplies 

 in the winter quarters. A friend of mine, who was for some time sta- 

 tioned at an infirmary at Kikombo, on the high plateau southeast 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 sjtecies, though 

 occasionally a few birds of different type might be noticed in the larger 

 ffocks. Towards the end of March, without any observable change in 

 climatic or atmospheric conditions, nine-tenths of the birds suddenly 

 disappeared, and oidy a sprinkling remained. These, which had pre- 

 A'iously been lost amid the myriad of winter visitants, seemed to consist 

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

 and H. soief/dlcnsis. One, described as white underneath, is probably 

 H. a'tkiopicH; and the fourth, very small and quite black, must be a 

 PsaHdoproene. All these remained through spring and summer. The 

 northward movement of all the others must be through some imi)ulse 

 not yet ascertained. In many other instances observation has shown 

 that the impulse of movement is not dependent on the weather at the 

 nu)ment. This is especially the case with sea birds. Prof. Newton 

 observes that they can be trusted as the almanac itself. Foul weather 

 or fair, heat or cold, the ])uffins, FrutercnJa arctica, rei)air to some of 



