MIGRATION. 791 



the days of their arrival and departure can be predicted as if they 

 were satellites revolving round the earth. "Foul weather or fair, 

 heat or cold, the puffins make their appearance at the proper day as 

 promptly as if they were moved by clockwork." While the course 

 of the migration of rodents and locusts is determined by conditions 

 so complicated and irregular that they may be called accidental, the 

 northward journey of birds is often directed to a definite spot thou- 

 sands of miles away from the starting point, and the resemblance 

 between irregular migration in search of food and the migration of 

 birds is too imperfect to tell us much about the origin of the 

 latter, which resembles more the movements of fishes like the 

 shad, which at a definite season enters upon a journey along a defi- 

 nite path to a spot hundreds of miles away, to return again after the 

 purpose of the journey is accomplished. 



Since the number of shad which enter a river in the spring is 

 out of all proportion to its resources as a feeding ground, we might 

 say of them, as we are disposed to say of birds, that they leave their 

 birthplace in search of food; but as they find so little food in the 

 rivers that it may be said, with almost literal exactness, that they 

 make their journey fasting, it is quite plain that this is the wrong 

 point of view; that we must believe they enter the river to lay their 

 eggs, and that we must see in this, and not in the return to the ocean, 

 the purpose of the migration. 



As the shad is a marine fish which does its eating at sea, and as 

 its visits to fresh water are only for the purpose of reproduction, 

 the numbers which make their way up the rivers are out of all pro- 

 portion to the capacity of the streams for supplying them with food. 

 The shad enters the mouths of our rivers in the spring in great 

 schools, and travels up them to a most surprising distance; for the 

 total length of the journey from the sea to the spawning ground and 

 back again often exceeds a thousand miles, and this journey is made 

 almost or quite without food. Many of them, and among these 

 the largest fishes, go on until they meet some insurmountable ob- 

 stacle, such as a waterfall or a dam, or until they reach the head 

 waters of the river. Before dams were built in the Susquehanna, 

 many shad which entered the Chesapeake Bay at the Capes con- 

 tinued their long-fasting journey across Virginia, Maryland, and 

 Pennsylvania into the State of New York, and traveled through 

 more than iive hundred miles of inland waters on the journey up- 

 ward. 



Fragments of Indian pottery, stamped with a pattern made by 

 the impression of a shad's backbone, have been found in southern 

 New York, and the number of stone net-sinkers which have been 

 picked up in the Wyoming Valley shows that the Indians had known 



