124 STUDIES IN LIFE AND SENSE. 



storks, wild ducks, wild geese, and many other species also migrate 

 in bands. The cranes and stalks fly in a vast triangular cloud, 

 guided by a leader, who retires periodically, and whose place is suc- 

 cessively filled by other members of the band. Of birds which present 

 peculiarities in their mode of journeying, the skylarks may be cited. 

 These latter birds arrive on the Norwegian coast in " a straggling 

 stream ; ' at first, whilst a little later enormous flocks appear. In the 

 case of many species of birds flying northwards in spring, the males 

 are the first to arrive, and precede the females by several days, or, it 

 may be, by several weeks. Such a peculiarity is not noticeable in the 

 southward migration taking place in autumn. It is likewise interesting 

 to note that many birds appear to wait for "favouring gales." The 

 quails select a favourable wind for their flight, although it happens 

 that these birds are annually drowned in large numbers in the passage 

 of the Mediterranean Sea. This sea is, in truth, the great Rubicon 

 of the migrants. It is crossed, by way of Greece and Cyprus, at 

 Sicily, at Malta, or from the South of Spain. By crossing at these 

 points, land is necessarily kept more or less constantly in sight. The 

 young birds of each year frequently migrate alone, their parents 

 having preceded them in their southward flight. It is a well-ascer- 

 tained fact that the young of some birds which spend the colder 

 season in the North of Africa may pass the first winter of their lives 

 in the South of Europe this latter feature presenting us thus with 

 probably a recent modification of the migratory habits of the species. 

 The old birds lead the way in cases where the young brood accom- 

 pany their parents to the warm and autumnal residence. We may 

 lastly note that migratory habits, as just remarked, are themselves 

 susceptible of modification. Although human observation serves 

 but as a " brief chronicle " of a brief time, we yet know sufficient of 

 the alteration of the habits of certain species of birds to warrant the 

 assumption that, under favourable conditions, the journeyings and 

 range of habitat of birds may be altered. Mr. A. R. Wallace cites 

 a typical instance of this kind in the case of a Mexican swallow. 

 This bird first appeared in Ohio in 1815. Its range of habitat 

 gradually increased in extent, since the year 1845 found this bird 

 in Maine and Canada ; whilst at present it is found as far north as 

 Hudson's Bay. The cliff swallow of North America is regarded as 

 having extended its distribution eastwards from the Rocky Mountains 

 to the eastern coast of the continent within the past century or so. 

 Similarly a species of wren has extended its range northwards in 

 America in past years and the rice-bird, originally confined to a few- 

 districts, has extended its range of distribution as its food was more 

 widely cultivated, and is now found wherever rice is grown. 



The facts relating to migration which occupy the preceding part 

 of this article may be regarded merely as a somewhat extended 



