BRITISH BIRDS. 77 



it is pushed on by the crowd behind, and is unable to get out of the 

 way. Mr. R. Gray ('Birds of the West of Scotland,' p. 122) saw "near 

 Girvan, about eight or nine years ago \ji.e. from 1871], numbers of Larks, 

 wdiich were incalculable, crossing one of the roads ; the mass of birds was 

 so compact that none of those in a line with the telegraph-wires escaped. 

 As soon as the flock passed, dozens were picked up dead or mutilated, 

 portions of wings, torn from the living bird, being even found adhering to 

 the wires." 



Mr. W. H. Hudson says (P. Z. S. 1872, p. 845) of the Swallows of 

 Buenos Ayres : — " When the season of migration approaches, they begin to 

 congregate, . . . but seem preoccupied or preyed upon by some anxiety which has 



no visible cause The birds seem to forget their songs and aerial recreations ; 



the attachment of the sexes, the remembrance of the spring is obliterated ; 

 they already begin to feel the premonitions of that marvellous instinct that 

 urges them hence : not yet an irresistible impulse, it is a vague sense of dis- 

 quiet ; but its influence is manifest in their language and gestures, their wild 

 manner of flight, and listless intervals. The little Atticora cyanoleuca dis- 

 appears immediately after the other, larger species. Many stragglers continue 

 to be seen after the departure of the main body ; but before the middle of 

 March not one remains, the migration of this species being very regular." 

 The writer in the above speaks of instinct ; but I attribute the cause of " the 

 irresistible impulse " to a corporeal sensation, a fever which I name 

 " migratory impulse " — irresistible, no doubt. Mr. Hudson says, in addition, 

 of ff. leucorrhoa, " Late in April, after almost all the other passage birds had 

 ceased, these continued to appear : the weather was already cold ; and all 

 these late comers flew with great celerity and as directly north as if their 

 flight had been guided by the magnetic needle." 



Mr. George Henry Lewes, in ' Problems of Life and Mind,' in the 

 chapter on "Psychological Principles," vol. i. p. 168, says :— " An animal 

 suffers from a physical calamity, seeks to escape from it, but never to under- 

 stand and modify its causes. He has only the logic of feeling to guide his 



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