ORDER OF MIGRATION ACCORDING TO AGE AND SEX 101 



Birds, 1 unreservedly follows the old traditional views, commencing 

 the section on the ' so-called migratory instinct/ with the following 

 statement : ' Direct observations in Nature have yielded the result 

 that among flocks of migrants the older and stronger individuals 

 are in general the leaders of the migratory host.' He could not, 

 however, have begun the treatment of this question with a more 

 unfortunate assertion ; for there is no one who has ever made obser- 

 vations which might support this view, nor is there any possible 

 way of determining which of the individuals of a migratory flock, 

 travelling at a height of a thousand, or even only five hundred, feet, 

 are older or younger birds. Among the few species which fly 

 during their migrations at low elevations, rarely exceeding five 

 hundred feet, such as Hooded Crows, Starlings, and Larks, a distinc- 

 tion between the old and young birds, while on passage, can only be 

 made in the case of Starlings, in which the two stages of age are 

 characterised by marked differences in the colour of the plumage. 

 These birds, however, as well as Hooded Crows and Larks, travel in 

 such irregular, ever-shifting swarms, that there can, apart from all 

 other such considerations, be no question of leadership in their case. 

 This, however, is, so far as my experience goes, the manner in which 

 the majority of birds migrate, the only exception being a few Waders 

 and aquatic birds, viz. the Curlews, Cranes, Geese, and related 

 species, which pursue their migration-flight either at an acute angle 

 of very generally unequal legs, or merely in a long oblique line. 

 Among these, it is true, the individuals at the head frequently change 

 places with others, but it is impossible to bring forward even the 

 shadow of a proof that the birds flying at the head of the column 

 are the older and stronger members of this particular assemblage. 

 Body-size is not admissible as a determining factor, nor are 

 such differences of size as may exist, sufficiently important to be 

 observable at the great height at which the migration proceeds ; 

 nor is colour, even where such is still distinguishable, any better 

 criterion of the age of individuals in the case of the species under 

 consideration. 



Dr. Weissmann (On the Migration of Birds 2 ) likewise accepts the 

 usual tradition, and in one of his lectures expresses himself as 

 follows : ' In the case of most birds, the oldest and most experi- 

 enced members of the flock i.e., those which have often performed 

 the journey before, travel at the head of the migrant host, and show 

 the others the way.' Here the question at once suggests itself: if 

 this applies only to ' most birds,' what becomes of those who have 

 no such leaders ? 



1 Zugstrassen der Vtigel, Leipzig, 1876. 



2 Ueber das Wandern der Vogel, in Gatke. 



