46 THE MIGRATION OF BIRDS. 



{Calidris arenaria and Tringa honaparti) are even 



reputed to have bred in the southern hemisphere, 



the former as far south as Lord Howe's Island, and 



the latter in the Falkland Islands, which, if true, 



strongly confirms a previous Antarctic habitat. At 



least twenty species of Charadriin^ birds from 



the Arctic regions visit Australia during winter ; 



as many more probably reach South Africa and 



South America at that season, in addition to the 



sedentary species. 



One may very naturally ask the reason for these 



vast extended flights.^ Why are they undertaken 



for no object that man can determine ? Migration 



is by no means a habit subject to caprice ; nor do 



birds ever undertake it either in space or time 



without serious cause. I am of opinion that these 



long journeys, some of them reaching over 140 



degrees of latitude, or nearly 10,000 miles direct, 



are the result of the transfer of these species from 



the North Polar Basin to the South Polar Basin, 



^ The suggestion made by Mr. Harvie-Brown {Report, Migra- 

 tion of Birds, iv. p. 71), that it is owing to the hardiness of 

 constitution of birds bred in high Arctic latitudes that their fly- 

 lines are so extended ; and also to the annual overflow of 

 enormous numbers pressing from behind and urging on to the 

 south those in the van, needs little to refute it. The Knot 

 {Tringa caniitus) is given as an instance. Unfortunately for 

 this ingenious theory, the Knot is bred in a high temperature, 

 just in the very height of the short Arctic summer, and begins 

 to draw south as soon as it can fly. It has, therefore, at no 

 period of its existence any experience of the rigours of an 

 Arctic climate ; but, on the other hand, lives almost in perpetual 

 summer or spring. Strength of constitution seems to have 

 no effect whatever on the length of migration flight; the 

 influences are of a far more deeply-rooted character. 



