CHAP. xx. ORDER OF MARCH. 255 



vain to look for it until the next season of migration comes 

 round, when, given the necessary wind and weather, the 

 appearance of the bird may confidently be expected. 



The period of migration of each species lasts about a 

 month. In spring, during the first week, the flocks consist 

 principally of adult males ; during the second week, they 

 principally consist of adult females; in the third week, 

 follow the birds of the year ; whilst finally, during the last 

 week, arrive the cripples birds which have lost their 

 toes, birds with half a tail, birds with one mandible 

 abnormally long, or birds with some other defect. In 

 autumn the order of migration is somewhat different- 

 For weeks before the regular period of migration is due 

 stragglers in various stages of plumage arrive, loaf about 

 in a desultory manner for a few days, and then disappear. 

 Some of these birds are in summer plumage, some of 

 them in their winter dress, whilst others are in a tran- 

 sition stage, moulting as they migrate. These avant- 

 courriers are supposed to consist of barren birds, odd birds 

 who have been unable to find a mate, or birds whose nests 

 have been destroyed too late in the season to allow of a 

 second nest to be made. Having nothing else to do, the 

 hereditary instinct to migrate not being checked by the 

 parental instinct, they yield to its first impulses, and drift 

 southwards before the general body of their species. When 

 the period of migration sets in in earnest, astounding as 

 the fact is, it is nevertheless true that the birds of the 

 year are the first to migrate, birds which of course have 

 never migrated before. This circumstance, which all the 



