Vol \w 



1913 



Pbillips, Migration mui Periodic Accuracy. 201 



Hunts of winter. In other words, a huge and far-extending 

 altruism, with nothing left to chance or to orthogenetic tendencies. 



This \ iew is. 1 think, farfetched, for one cannot see how the earliest 

 spring movements are the necessary outcome of a rush to occupy 

 all available territory. We should suppose that many more birds 

 could migrate at the same time without disturbing the geographical 

 economy of seasonal dispersal. 



Loomis -aw in the case of the Canada Goose a continuous 

 migration, not subject to a sudden arousing of the migratory 

 impulse. The impelling force came in this ease, he thought, 

 more from without. Hut here it seems he is only partly right, for 

 this species is certainly subject to great and sudden migratory 

 impulses, only, as we have mentioned above, there is added an 

 element o( choice, or an ability to profit by external conditions 

 which is not often easy to see in other birds. 



Loomis's various papers in 'The Auk,' in so far as they refer to 

 the erratic movements of birds, and peculiar periodic dispersals, 

 are very interesting, but cannot be considered here. See also an 

 instructive paper by Whitaker on the great invasion of southern 

 Europe by Crossbills in 1909. 1 Even such cases oi sporadic in- 

 vasion of new territory may show an orderly progress and just as 

 orderly retirement. 



Many theories of course have been put forward to account for 

 the start of vernal migrants from winter quarters. An ingenious 

 one is that of Taverner -. who saw in the breeding of tropical spe- 

 cies an actual stimulus to wintering migrants. This stimulus was, 

 he thought, brought about by pressure of numbers and lack of food 

 owing to increase in resilient numbers by their early breeding, the 

 pressure extending outwards (northwards) to the limits of popu- 

 lated ground. Other writers have -ecu in the failure of the iood 

 supply in the South after the advent of the dry season, a sufficient 

 inciting cause, but it is hardly probable that any of these reasons 

 Could account entirely for the orderly procession of different species, 

 and their appearance at allotted times. 



It remains to search for other examples of a physico-chemical 



Whitaker, .' I 9 . Auk. 1910, p 

 • Auk. 1904, p. 322. 



