PROTECTIVE MOVEMENTS 



367 



curious that year after year the birds will follow the same routes, 

 even coming out of their way many miles to go with the flock. It is 

 probable that the older birds lead the migrations, and that the paths 

 are kept by force of imitation. The young follow, and the older ones 



FIG. 185. Migrating fish 



Humpbacked salmon jumping low falls, Litnick Stream, Alaska, on way to breeding 

 grounds. (From photograph by United States Bureau of Fisheries) 



continue to do as they have always done. As a result, customs are 

 established that persist even when they cease to be of greatest 

 advantage or economy. 



Migrations of fishes have also been recorded, and these 

 seem to be related chiefly to finding safe breeding places. 

 Some, like the eel, will go out into the ocean to breed ; others, 

 like the salmon, will spend most of their time in the ocean and 

 will come up into the rivers to breed (see Fig. 185). 



