/. A. ALLEN. 37 



the young birds of the year, which have never before made 

 the journey, are the first of their species to move south, or, 

 in other words, precede their parents. Others claim that 

 some of the first birds to leave are always old birds, and 

 that they act as guides to the inexperienced young birds. It 

 is evident, however, that it matters little which view be cor- 

 rect, for in either case the young birds become mingled with 

 the general throng bound on their southward journey and 

 are not dependent on either their own resources or on other 

 members of their own species for direction. 



This implies, of course, strong memory on the part of the 

 old birds, proof of which is not wanting in their ability to 

 find their way back, spring after spring, to their accustomed 

 nesting-places — not merely to the same general region, but 

 to the same tree or cliff or other shelter to which the 

 same pair of birds return year after year for many years. 

 This being true — in proof of which there is much strong 

 evidence — it is easy to believe that they can readily recall 

 the general features of the country they may have to cross in 

 their semi-annual wanderings. 



Birds exercise more or less choice in respect to meteor- 

 ological conditions in regulating their migratory journeys. 

 They prefer fair weather, and do not generally attempt pro- 

 tracted flights during overcast or stormy weather. The 

 direction and force of the wind seems a secondary considera- 

 tion, but at times undoubtedly exerts considerable influence. 

 Temperature, however, is the most important condition ; a 

 considerable decline hastening the migratory movement in 

 autumn and greatly retarding it in spring, at which season, 

 a severe and protracted period of cold weather may check 

 the advance for days together. A warm wave in spring, on 

 the other hand, greatly hastens the advance and gives rise 

 to a coincident "wave of migration," so familiar to all 

 field-observers, marked by a sudden and great increase in 

 the number of birds, as regards both species and individ- 

 uals, at a given point. 



