MIGRATION. 285 



the northern climates, and it is exceedingly rare to 

 find the young ones there." 



To this we may subjoin such observations of other 

 continental writers on the general subject as have not 

 already been anticipated. 



M. Ul. Ekstroem, in his Observations upon the 

 Birds of Passage in Sudermania in Sweden, states 

 the following, among other interesting facts, which 

 were the results of long and careful observation. Birds 

 of passage generally migrate with a contrary wind. 

 Several species do not follow the same meridian in 

 arriving and departing, and they are, therefore, only 

 seen once a year in the same districts. In Suder- 

 mania several species which were formerly very rare 

 are now very common, and vice versa. He gives an 

 opinion upon the causes which engage or compel 

 birds to change of country. Without disputing that 

 difference of temperature and nourishment have much 

 to do with it, he is inclined to consider that habit 

 is quite as much concerned ; according to him the 

 recollection of the old ones that they have made the 

 journey, carrying the young with them, and the 

 u instinct of travel," which, at certain periods, affects 

 them with a real nostalgia, must be considered, 

 especially the last, as the principal and immediately 

 exciting cause of these migrations. He shows, by 

 examples, that the failure of food alone cannot be the 

 cause, as some birds leave at the period when their 

 proper food is the most abundant; and generally 

 the birds of passage arrive and depart at the usual 

 periods, whatever be the state or prospects of the 

 season *. 



M. Brehm, who has given much attention to the 

 subject of the migration of birds, considers the fol- 



* Review in * Bulletin Universe!,' of M. Ul. Kkstroem's 

 ' Observations sur les Oiseaux de Passage dans la Sudermanie, 

 en Suede.' 



