Page:Popular Science Monthly Volume 52.djvu/813

Rh 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 thousands 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 definite 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 proportion 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 obstacle, 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 continued their long-fasting journey across Virginia, Maryland, and Pennsylvania into the State of New York, and traveled through more than five hundred miles of inland waters on the journey upward.

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