MIGEATION. 



37 



so much more tender than that of adults, that they were in the worst condition ; the old 

 feathers were no better than rusty rags. 



The most interesting fact in connection with this single moult of the Swallow is that 

 it takes place in March instead of September. The natural inference to be drawn from 

 such a circumstance is, that the Swallows belong to the southern hemisphere, and have only 

 comparatively recently (probably in post-glacial times) emigrated to the Palsearctic or 

 Nearctic Regions. This theory is confirmed by a glance at their geographical distribution. 

 The genus Hirundo, as restricted by Sharpe in the ' Catalogue of Birds,' contains 27 

 species, of which 16 breed only in the Ethiopian Region, 2 both in the Ethiopian and 

 Oriental Regions, 2 only in the Oriental Region, 1 both in the Oriental and Palsearctic 

 Regions, 1 both in the Oriental and Australian Regions, 2 only in the Australian Region, 

 2 only in the Neotropical Region, and the remaining 1 both in the Nearctic, Patearctic, 

 and Ethiopian Regions. Of the 11 genera recognized by the same author, Hirundo is the 

 only one which is cosmopolitan in its range ; 2 are confined to the Ethiopian, and 1 each to 

 the Australian and Neotropical Regions, whilst no genus is confined to the Palaearctic or 



Nearctic Regions. 



The evidence that the Swallow had an Antarctic origin seems to be 



conclusive. 



It not unfrequently happens that the breeding-range of a species overlaps its winter 

 range. Under these circumstances it is probably a rule, with scarcely an exception, that 

 the birds breeding in the overlapping part are residents who never migrate at all. The 

 habit of migration is not a whim. If, on an average of seasons, it is possible for the birds 

 to find food in their breeding-grounds during the winter, they doixbtless remain there. It 

 is scarcely conceivable that birds would brave the perils of migration without an adequate 

 cause. The mortality of birds on migration is very great ; many are caught in storms 

 whilst crossing the Ocean, as the dead bodies which are washed upon the beach often prove. 

 It is not an uncommon thing to find birds newly arrived at their destination — at Spern 

 Head, for example — so fatigued as to be readily caught by the hand. 



Little or nothing has been written of the migration of birds in the southern hemi- 

 sphere, but it is almost as important a fact in the history of the birds of Natal as in that of 

 British birds, though the difference in the geographic relations of the two countries modifies 

 the details in many ways. It is a remarkable fact that whilst there are very many birds 

 breeding in the northern hemisphere and wintering in the southern, it is not known that 

 any land-bird breeds in the southern hemisphere and habitually winters in the northern. 

 It seems probable that most of the accidental visits of southern species of land-birds to the 

 northern hemisphere which have been from time to time recorded are of doubtful 

 authenticity ; and amongst sea-birds this practice is confined to one or two species of Petrel, 

 of which it is not unlikely that undiscovered breeding-grounds exist in the northern hemi- 

 sphere. One cause of this apparent anomaly may be the difference in the distribution of 

 the land. North of the British Islands, and a similar latitude on the continent of Europe 



Emigration 

 of Swallows. 



Hirundo an 



Antarctic 



genus. 



Birds resi- 

 dent where 

 summer and 

 winter 

 quarters 

 overlap. 



Migration in 

 the southern 

 hemisphere. 



Few or no 



winter 



migrants 



from the 



southern 



hemisphere 



