164 Our Bird Friends. 



have heard different species talking to each other as 

 they passed over London. The migratory move- 

 ments of birds are in many respects very curious 

 indeed. For instance, no species belonging to the 

 northern hemisphere ever journeys south to breed, 

 and no winged inhabitant of the southern hemi- 

 sphere ever bends its coiu'se north in the spring to 

 propagate its species. All breeding movements are 

 in the direction of the Poles and away from tlie 

 Equator. 



An adequate supply of food lias no doubt been 

 the greatest cause in establishing migratory move- 

 ment; but this cannot be urged as a reason in all 

 birds, for there are instances where long journeys 

 are made and innunieral)le dangers encountered 

 without any apparent cause. 



These great spring and autumn movements take 

 ])lace over certain well-established tracks, called 

 " Hy-lines " by naturalists, and the mystery of 

 mysteries in regard to the travellers over them is 

 that durincT the autunm journey the birds that 

 know nothing about them from actual experience 

 go first. Out of three hundred and sixty different 

 kinds making the island of Ht^'ligoland in the 

 North Sea their temporary resting-place, only in 

 one single instance do the old birds precede the 

 young ones, and that is in the case of the Cuckoo. 



Migrants from Europe spend the winter in 

 Africa as a rule, and it is said that those breeding 

 farthest north in the sununer fly farthest south in 



